With its meaty 3.0-litre turbo-diesel engine and proper off-road smarts, the Isuzu D-Max and MU-X have become popular choices for touring and serious off-roading. The availability of a crew-cab or dual-cab for the D-Max as well as a styleside or cab-chassis option has ensured it can be put to a variety of tasks, while the MU-X’s seven-seat layout has kept it relevant for adventurous families.
The four-wheel-drive system was a fair dinkum one which used Isuzu’s Terrain Command rotary dial to switch between two-wheel-drive, four-wheel-drive high-range and four-wheel-drive low-range where the 2.48:1 reduction ratio applied.
Regardless of what body style you chose, the powerplant was the same; a large capacity four-cylinder turbo-diesel that cranked out 130kW of power and 380Nm of torque from as low as 1800rpm. Transmission choices were limited to a five-speed manual or five-speed conventional automatic but it’s fair to say the majority out there for sale second-hand have the cost-optional auto fitted.
The big difference between the D-Max and MU-X (body style and interior packaging aside) is that the D-Max got a conventional leaf-sprung rear axle, while the MU-X scored a better-riding, independent coil-sprung set-up. Both variants used a body-on-frame construction with a ladder chassis.
Rugged and generally dependable, the Isuzu twins have racked up plenty of kilometres between them and plenty of fans along the way. But, as with any used vehicle, there are things to watch for and things you can change to make them better.
WORDS DAVE MORLEY, PHOTOS ARNOLD ARCHIVE
The Isuzu D-Max and MU-X twins are popular amongst the 4X4 fraternity because of the simple, hard-working engine and reliable mechanicals. But, it’s not all smooth sailing, here are some of the problems and solutions we’ve heard about.
VEHICLES
Creaky joints
Like plenty of other off-roaders with independent front suspension, the Isuzus can experience a very short front CV joint life. The wear and tear associated with big wheel articulation, big tyres, not to mention attack from water and whatever else can contaminate the joint, and you can be chewing out front CVs at an alarming rate.
The situation is eased by never driving off-road and never driving hard, but whoever bought one of these to avoid that sort of fun? And even underground car-parks with their tight spaces and twists and turns like a politician before an integrity commission, can use up a CV joint (not just an Isuzu one) in double-quick time.
The best advice is to replace these as with any other service item and never have to worry about them again. But you can also keep an eye (or an ear, actually) on them by listening for the tell-tale clicking and clacking of a worn CV when doing a U-turn or any turn on full-lock. Of course, by that stage of the game, the joint is already shot.
Make sure the rubber boots are also kept in good shape and even the smallest nick or split in the rubber means curtains for the CV within. Even if you don’t want to change them periodically, at least have them inspected at every service.
When the CVs are being replaced. Make sure you fit good quality units. Most of them these days are coming out of China and, at the risk of starting a trade war, they’re generally not as good as the CVs being made in Japan. Yes, the Japanese ones might cost more, but it’s definitely a conversation worth having with your service workshop to make sure the replacements aren’t going to fail even faster than the OE stuff.
And if you do manage to find a Japanese-made CV at a good price, buy a few sets and have them ready for next time. And don’t forget to replace the boots at the same time.
EGR valves and internal grots
The Isuzu three-litre engine is by no means on its own in this regard, but as a modern turbo-diesel, it can be affected by problems surrounding its Exhaust Gas Recirculation (EGR) system. In line with emissions controls mandated by the governments of the world, an EGR valve allows the Isuzu engine to consume a percentage of its own exhaust gas as a means of cleaning up tailpipe emissions by burning that portion of its exhaust twice.
But the EGR valve is also involved in ensuring that crankcase fumes get burned in the engine and don’t escape into the atmosphere, and that’s where the ducks of doom start to line up. Those exhaust gasses that are given a second trip through the engine contain soot (a normal component of a diesel’s exhaust emissions) and when they combine in the EGR valve with the oily fumes from the crankcase, the oil and soot can quickly turn to a black, sticky gunge that can clog up the EGR valve and coat the inlet manifold, reducing its effective diameter.
Like we said, this is anything but an Isuzu phenomenon, but it’s something that no owner of a modern turbo-diesel can safely ignore. If it’s allowed to go unchecked, the layers of oily soot soon build up and the EGR valve becomes jammed open. At which point the vehicle’s emission-controls aren’t working and it’s – technically - unroadworthy.
The other symptoms can include a check-engine light illuminating on the dashboard as well as poor starting, a loss of power, reduced fuel economy, and rough idling.
The best advice is not to wait until the EGR and intake manifold clogs up. Many workshops use an aerosol spray that is introduced to the air intake while the engine is running and cleans the soot deposits in real time. The recommendation is to have this done at every service, and while the treatment can easily cost $100 a pop, it’s still cheap compared with the alternative.
Which is, of course, to disassemble the EGR valve and the inlet manifold and plumbing and manually clean the grot out of it. This is not a simple job, if only because of the degree of disassembly required to get to the affected bits and pieces. Suddenly, that hundred-buck shot of aerosol is looking pretty cheap.
And even if you do go down the hand-cleaning route, there’s no guarantee that the EGR valve will come back to life. Most experts agree that once the valve has become stuck open, it’ll almost certainly need to be replaced at a cost of anything up to $1500.
Some owners reckon the best modification is to disable (block off) the EGR valve and therefore prevent it working at all. But that’s not actually a very good idea at all. The practice is highly illegal and the fines for an individual tampering with a vehicle’s emissions-control system can be massive. And it’s worse for a business, which is why most workshops will run a mile before agreeing to carry out this modification. Don’t do it, basically. And aside from leaving yourself open to a monster fine, the car will also be rendered technically unroadworthy and you might even find your insurance company will use such a modification as a reason to not return your calls.
A bit light on
A lot of people using D-Maxs for work have found that the standard suspension is a bit underdone for carting around really big loads like loaded service bodies and such. Load them up and there’s just too much rear sag and that translates to iffy steering and a loss of braking performance in a big emergency. Not to mention that a truck making like a dog with worms is just horrible to drive.
A GVM upgrade is possible through new suspension and there are kits around that are already certified and will do the job. Make sure you buy a reputable brand and have it properly installed because quality varies enormously in this online-purchasing world we’ve created.
Generally speaking, you’ll be replacing springs and shocks but you might also need to change out bump stops and check for any duff bushes and shackles while you’re in there.
You might as well also add a two-inch lift as this will not only give the vehicle even greater load carrying ability, it’ll also make it more fun and more capable off-road. A two-inch lift mightn’t sound like much, but it can be all the difference in rough going.
Don’t be tempted to go more than two inches (45mm) though unless you like roadside chats with the boys in blue and you’re prepared for your insurance company to disown you should the unthinkable happen.
Workshops we talked to advised against air-bag helper-springs on the D-Max ute as the chassis design at the rear isn’t rally compatible with them. The big danger is that the air-bags suddenly put strain on an area of the chassis not designed for such a load and a broken back is the result. It sounds bizarre, but it’s happened often enough that some workshops won’t fit air-bags to anything.
Hot tranny
Some owners of D-Maxs or MU-Xs have found that the vehicle’s five-speed auto can get hotter than they’d like it to be when using the vehicle hard. By hard, we don’t mean at highway speeds of when simply off-roading, but hard as in towing a 2.5-tonne caravan on a long, windy, uphill section of road.
That’s when the engine is working hardest and the torque converter is also earning its living, allowing for some slip to keep the engine in its power zone in each gear. Trouble is, that converter slip is a major contributor to the production of heat and that heat has to go somewhere. In most cases, that somewhere is the factory trans cooler which is part of the radiator’s bottom tank. In turn, that makes the radiator coolant hotter which makes the engine run hotter and suddenly you have yourself a nice little vicious circle of heat-creep. And if there’s one thing an automatic transmission hates, it’s heat.
In the first place, the best thing to do is get an idea of what’s happening to your trans temps before rushing out and buying more hardware. You can get a ScanTool or ScanGauge that interfaces with the vehicle’s on-board diagnostics and can tell you lots of useful things the standard dashboard doesn’t. Things like real-time trans temperature, for instance.
Once you have that info, you can move on to a fix. Or maybe not; if the temps don’t get to a point where you should be worried. Yes, the Isuzu has a transmission-temperature warning light that will illuminate, but like most of these warning lights, the damage is often done by the time the light flickers on. In fact, the trade suggests that the warning light only comes on at a temperature of 134-degrees, which is way beyond what we’d be happy seeing. Under 100-degrees is far better, and lower is better again since auto trans experts will tell you there’s no such thing as over-cooling an auto.
The other solution to the problem is to drive around it. Don’t let the vehicle select a too-high gear on a twisting uphill road. Manually pull it back a gear, allowing the engine to get into its comfort zone and the torque converter to slip less, thereby producing less heat.
Also, keep an eye on things in the longer term. Check the colour and smell of your trans fluid. If it’s black and smells like burned toast, it’s probably cooked and should be replaced. And when you do have the tranny serviced, ask for the old filter, take it home and cut it open to check for any black, solid deposits that could be burned bands or clutch material.
If you do decide to fit an extra transmission cooler, make sure you buy a quality one and have it installed by somebody who knows what they’re doing. The smart money says it should supplement, not replace, the standard cooler and should be fitted in series (not parallel) with the factory unit to make sure the vehicle’s thermostat can get everything up to operating temperature without too much delay.
Isuzu’s official line is that the D-Max and MU-X are already fitted with a heavy-duty trans cooler from the factory, so no additional hardware should be required. Tranny experts disagree, but the best bet would be to find a fitter that will warranty their work as an aftermarket cooler that failed would almost certainly give Isuzu the option of walking away from any warranty claim.
Those DPF blues. Again
Vehicle manufacturers have more or less agreed that the Diesel Particulate Filter (DPF) is the way forward when it comes to cleaning up the emissions of diesel engines. But the DPF has a problem, and it’s one that affects not only the Isuzu models we’re talking about here, but pretty much all vehicles that use the technology.
That problem becomes a bit more understandable when you consider the front-bar names for a DPF; soot filter or soot trap. Yep, the DPF’s role in life is to trap some of the harmful emissions, store them and then burn them off at a later date. Why doesn’t it just burn them off and turn them to ash in real-time? Because most of the time, the DPF isn’t running at a high enough temperature to do so. And there’s the second part of the problem.
Until you get the engine and exhaust system hot enough for the burn-off to occur, it won’t (can’t) happen. So, if all you do is lurch about the city and suburbs in your D-Max or MU-X, pretty soon the DPF will be full of soot, the warning light will appear on the dashboard and you’re up for the not insignificant cost of having the filter manually cleaned. Or replaced, if you’ve been really unlucky.
Sometimes a good run down a road at a decent speed will be enough to get the engine hot enough to allow the DPF to burn off. Other times it won’t be, which is when you have to take a deep breath and front up at a workshop to have the filter either manually cleaned or, in extreme cases, replaced outright.
The biggest modification you can make to avoid the DPF becoming clogged is to modify your driving patterns. Make sure you take the old girl for a half-hour strop up a freeway at freeway speeds (not sitting in gridlock like most freeways) every month or so, That gives the exhaust system (and the DPF) the chance to get hot enough to do its regeneration thing and save you all those headaches.
Some geniuses will also tell you to bypass the DPF altogether. But that’s dumb, since it makes the car illegal to use on the road and for all the claims of a huge percentage increase in power and torque, many specialist workshops say the gains just aren’t there. That said, you can buy a kit that deletes the DPF but take it from us, its strictly for competition, non-road-going cars. And ironically, a competition car that is driven flat out everywhere is one that wouldn’t have DPF problems in the first place.
What’s that tapping noise?
The Isuzu 3.0-litre turbo-diesel doesn’t have hydraulic valve-lash adjustment, so checking and setting the valve clearances is a routine maintenance job. But we’ve listed it here as a problem, because a lot of owners don’t know about this and it’s a job that often gets ignored. That’s the bad news. The good news is that the adjustment is via screw-and-locknuts, rather than the vastly more fiddly and difficult shim-and-bucket design. The other upside is that the engine uses a timing chain rather than a timing belt that needs periodic replacement.
You’ll be able to identify poor valve adjustment by a ticking noise from the top of the engine that is usually worst on cold start-ups. That’s if the valve clearances are loose, of course. If the valves are tight, you won’t hear a thing but the top end of your engine will be copping a hammering. Long term, you could easily damage the valve stems with loose clearances or damage a cylinder with not enough (tight) clearance.
Treat checking – and adjusting if necessary – valve clearances as a once-every-40,000km routine job. Make sure you fit new injector seals and a rocker-cover gasket at the same time, too, as only the greatest optimist in the world would ever re-use a gasket and think it won’t leak. Be sure not to over-tighten the rocker-cover (or it’ll crack) and make sure any grots that fall into the engine as you remove the rocker cover are picked out and not left to cause mayhem in the diesel’s upper-cylinder area.
There’s really nothing you can do to get around this maintenance chore. Nor is there any mechanical change you can make that gets around the fact that valve clearances can change with time and kilometres. However, we’ve never heard anybody blowing a motor to bits through servicing the engine regularly and treating it with some respect.
Front-wheel bearing wear
When you think about the life led by an off-road four-wheel-drive, it’s a wonder they last any time at all. In the case of the Isuzus, many owners have found that front bearing life is sometimes less than 50,000km. The problem there is that many of them only find out when they have new tyres fitted and the tyre shop phones to say that the wheel alignment can’t be done because there’s too much play in the wheel bearings. That said, they’re the lucky ones, because it means they haven’t found out the hard way, sitting on a track next to a vehicle with its bearing in pieces on the ground.
Again, this is not a problem unique to Isuzus but it is one that can’t be ignored. But then, it doesn’t have to be if you make it part of your regular maintenance schedule.
This is a real simple one; have the front wheel bearings inspected and greased or replaced every 30,000km. Always use an appropriate grade and type of grease, remembering that, at some point during the next school holidays, the vehicle will be standing sills-deep in (possibly salt) water.
You can re-pack the bearings yourself if you know how to spot the wear signs, or a workshop can do it pretty cheaply as an add-on to your regular oil change service. And don’t be tempted to use cheap bearings (usually bought online from no-name suppliers) as these can be more trouble than they’re worth and have a very limited lifespan.
When you re-grease bearings, remember that unless you have have a small bead of grease forming at the seal, the bearings are probably not full of grease. You can also extend bearing life by letting your vehicle (and the hot wheel bearings) cool down before plunging into a cold creek or river. The thermal shock involved in not doing this can make the bearings take a big gulp of water, rather than the seals keeping it out.
Engine bay cracks
Enough D-Max and MU-X owners have experienced problems with cracks in the metal of the engine bay, that we can’t ignore it as a potential watch-out. It seems the cracks are caused by either stress or metal fatigue and are most likely to show up on the suspension towers, near the VIN plate or low down on the inner guards.
Chassis have been cracked , too, mainly at the front where big, heavy bull-bars and winches have been fitted, effectively cantilevering off the rails. It seems as though the way the Isuzu chassis is constructed allows for the front rails to flex and that, in turn allows the bulbar to `rock’ from side to side, magnifying the metal-stressing effects.
The only 100% foolproof, legal way to fix the cracks in the engine-bay sheet-metal involves replacing those parts of the bodyshell structure. Not cheap, and definitely not easy. In fact, it’s a big bodywork deal in most cases.
Yes, you can weld the cracks up but at that point, you’re technically altering the crash signature of the structure and that’s kind of a no-no when it comes to the way the car performs in a shunt. It could alter the way the air-bags work, too, but then so does fitting a big bulbar. That said, we know which way most owners will go.
As for the front rails, the best advice is to use the lightest bull-bar that will still do the job and think about where you mount a winch.
Instead of plonking a winch way out front where it has the maximum leverage on the chassis members, it might be better to mount it back towards the front axle, maybe on a cradle that bolts between the rails (as if you were using an alloy bull-bar). That way, you’ve taken a huge amount of stress off the rails and that’s got to be good news. That said, our experts reckon there’s a limit to this before the winch gets in the way of the air-con condenser and everything else at the front of the engine bay.
Be careful where you mount a second battery, too, as the extra mass of a big battery could easily lead to the sort of engine-bay cracks reported. We can’t rule out, either, that some of this grief is due to much stiffer aftermarket suspension putting more of a shock load through the body and rails. Be careful how high and how stiff you go when lifting or attempting to improve the load carrying of an Isuzu (or any other make and model) and be careful how radical you go suspension-wise.
VEHICLES
With its meaty 3.0-litre turbo-diesel engine and proper off-road smarts, the Isuzu D-Max and MU-X have become popular choices for touring and serious off-roading. The availability of a crew-cab or dual-cab for the D-Max as well as a styleside or cab-chassis option has ensured it can be put to a variety of tasks, while the MU-X’s seven-seat layout has kept it relevant for adventurous families.
The four-wheel-drive system was a fair dinkum one which used Isuzu’s Terrain Command rotary dial to switch between two-wheel-drive, four-wheel-drive high-range and four-wheel-drive low-range where the 2.48:1 reduction ratio applied.
Regardless of what body style you chose, the powerplant was the same; a large capacity four-cylinder turbo-diesel that cranked out 130kW of power and 380Nm of torque from as low as 1800rpm. Transmission choices were limited to a five-speed manual or five-speed conventional automatic but it’s fair to say the majority out there for sale second-hand have the cost-optional auto fitted.
The big difference between the D-Max and MU-X (body style and interior packaging aside) is that the D-Max got a conventional leaf-sprung rear axle, while the MU-X scored a better-riding, independent coil-sprung set-up. Both variants used a body-on-frame construction with a ladder chassis.
Rugged and generally dependable, the Isuzu twins have racked up plenty of kilometres between them and plenty of fans along the way. But, as with any used vehicle, there are things to watch for and things you can change to make them better.
The Isuzu D-Max and MU-X twins are popular amongst the 4X4 fraternity because of the simple, hard-working engine and reliable mechanicals. But, it’s not all smooth sailing, here are some of the problems and solutions we’ve heard about.
WORDS DAVE MORLEY, PHOTOS ARNOLD ARCHIVE
Creaky joints
Like plenty of other off-roaders with independent front suspension, the Isuzus can experience a very short front CV joint life. The wear and tear associated with big wheel articulation, big tyres, not to mention attack from water and whatever else can contaminate the joint, and you can be chewing out front CVs at an alarming rate.
The situation is eased by never driving off-road and never driving hard, but whoever bought one of these to avoid that sort of fun? And even underground car-parks with their tight spaces and twists and turns like a politician before an integrity commission, can use up a CV joint (not just an Isuzu one) in double-quick time.
The best advice is to replace these as with any other service item and never have to worry about them again. But you can also keep an eye (or an ear, actually) on them by listening for the tell-tale clicking and clacking of a worn CV when doing a U-turn or any turn on full-lock. Of course, by that stage of the game, the joint is already shot.
Make sure the rubber boots are also kept in good shape and even the smallest nick or split in the rubber means curtains for the CV within. Even if you don’t want to change them periodically, at least have them inspected at every service.
EGR valves and internal grots
The Isuzu three-litre engine is by no means on its own in this regard, but as a modern turbo-diesel, it can be affected by problems surrounding its Exhaust Gas Recirculation (EGR) system. In line with emissions controls mandated by the governments of the world, an EGR valve allows the Isuzu engine to consume a percentage of its own exhaust gas as a means of cleaning up tailpipe emissions by burning that portion of its exhaust twice.
But the EGR valve is also involved in ensuring that crankcase fumes get burned in the engine and don’t escape into the atmosphere, and that’s where the ducks of doom start to line up. Those exhaust gasses that are given a second trip through the engine contain soot (a normal component of a diesel’s exhaust emissions) and when they combine in the EGR valve with the oily fumes from the crankcase, the oil and soot can quickly turn to a black, sticky gunge that can clog up the EGR valve and coat the inlet manifold, reducing its effective diameter.
Like we said, this is anything but an Isuzu phenomenon, but it’s something that no owner of a modern turbo-diesel can safely ignore. If it’s allowed to go unchecked, the layers of oily soot soon build up and the EGR valve becomes jammed open. At which point the vehicle’s emission-controls aren’t working and it’s – technically - unroadworthy.
The other symptoms can include a check-engine light illuminating on the dashboard as well as poor starting, a loss of power, reduced fuel economy, and rough idling.
The best advice is not to wait until the EGR and intake manifold clogs up. Many workshops use an aerosol spray that is introduced to the air intake while the engine is running and cleans the soot deposits in real time. The recommendation is to have this done at every service, and while the treatment can easily cost $100 a pop, it’s still cheap compared with the alternative.
Which is, of course, to disassemble the EGR valve and the inlet manifold and plumbing and manually clean the grot out of it. This is not a simple job, if only because of the degree of disassembly required to get to the affected bits and pieces. Suddenly, that hundred-buck shot of aerosol is looking pretty cheap.
And even if you do go down the hand-cleaning route, there’s no guarantee that the EGR valve will come back to life. Most experts agree that once the valve has become stuck open, it’ll almost certainly need to be replaced at a cost of anything up to $1500.
When the CVs are being replaced. Make sure you fit good quality units. Most of them these days are coming out of China and, at the risk of starting a trade war, they’re generally not as good as the CVs being made in Japan. Yes, the Japanese ones might cost more, but it’s definitely a conversation worth having with your service workshop to make sure the replacements aren’t going to fail even faster than the OE stuff.
And if you do manage to find a Japanese-made CV at a good price, buy a few sets and have them ready for next time. And don’t forget to replace the boots at the same time.
Some owners reckon the best modification is to disable (block off) the EGR valve and therefore prevent it working at all. But that’s not actually a very good idea at all. The practice is highly illegal and the fines for an individual tampering with a vehicle’s emissions-control system can be massive. And it’s worse for a business, which is why most workshops will run a mile before agreeing to carry out this modification. Don’t do it, basically. And aside from leaving yourself open to a monster fine, the car will also be rendered technically unroadworthy and you might even find your insurance company will use such a modification as a reason to not return your calls.
The Drivetech 4x4 Enduro Pro remote reservoir monotube shock performs even better than it looks. The remote reservoir provides excellent heat dissipation to improve shock performance whilst allowing for extra shock travel when offroad.
A bit light on
A lot of people using D-Maxs for work have found that the standard suspension is a bit underdone for carting around really big loads like loaded service bodies and such. Load them up and there’s just too much rear sag and that translates to iffy steering and a loss of braking performance in a big emergency. Not to mention that a truck making like a dog with worms is just horrible to drive.
A GVM upgrade is possible through new suspension and there are kits around that are already certified and will do the job. Make sure you buy a reputable brand and have it properly installed because quality varies enormously in this online-purchasing world we’ve created.
Generally speaking, you’ll be replacing springs and shocks but you might also need to change out bump stops and check for any duff bushes and shackles while you’re in there.
Hot tranny
Some owners of D-Maxs or MU-Xs have found that the vehicle’s five-speed auto can get hotter than they’d like it to be when using the vehicle hard. By hard, we don’t mean at highway speeds of when simply off-roading, but hard as in towing a 2.5-tonne caravan on a long, windy, uphill section of road.
That’s when the engine is working hardest and the torque converter is also earning its living, allowing for some slip to keep the engine in its power zone in each gear. Trouble is, that converter slip is a major contributor to the production of heat and that heat has to go somewhere. In most cases, that somewhere is the factory trans cooler which is part of the radiator’s bottom tank. In turn, that makes the radiator coolant hotter which makes the engine run hotter and suddenly you have yourself a nice little vicious circle of heat-creep. And if there’s one thing an automatic transmission hates, it’s heat.
In the first place, the best thing to do is get an idea of what’s happening to your trans temps before rushing out and buying more hardware. You can get a ScanTool or ScanGauge that interfaces with the vehicle’s on-board diagnostics and can tell you lots of useful things the standard dashboard doesn’t. Things like real-time trans temperature, for instance.
Once you have that info, you can move on to a fix. Or maybe not; if the temps don’t get to a point where you should be worried. Yes, the Isuzu has a transmission-temperature warning light that will illuminate, but like most of these warning lights, the damage is often done by the time the light flickers on. In fact, the trade suggests that the warning light only comes on at a temperature of 134-degrees, which is way beyond what we’d be happy seeing. Under 100-degrees is far better, and lower is better again since auto trans experts will tell you there’s no such thing as over-cooling an auto.
The other solution to the problem is to drive around it. Don’t let the vehicle select a too-high gear on a twisting uphill road. Manually pull it back a gear, allowing the engine to get into its comfort zone and the torque converter to slip less, thereby producing less heat.
Also, keep an eye on things in the longer term. Check the colour and smell of your trans fluid. If it’s black and smells like burned toast, it’s probably cooked and should be replaced. And when you do have the tranny serviced, ask for the old filter, take it home and cut it open to check for any black, solid deposits that could be burned bands or clutch material.
You might as well also add a two-inch lift as this will not only give the vehicle even greater load carrying ability, it’ll also make it more fun and more capable off-road. A two-inch lift mightn’t sound like much, but it can be all the difference in rough going.
Don’t be tempted to go more than two inches (45mm) though unless you like roadside chats with the boys in blue and you’re prepared for your insurance company to disown you should the unthinkable happen.
Workshops we talked to advised against air-bag helper-springs on the D-Max ute as the chassis design at the rear isn’t rally compatible with them. The big danger is that the air-bags suddenly put strain on an area of the chassis not designed for such a load and a broken back is the result. It sounds bizarre, but it’s happened often enough that some workshops won’t fit air-bags to anything.
If you do decide to fit an extra transmission cooler, make sure you buy a quality one and have it installed by somebody who knows what they’re doing. The smart money says it should supplement, not replace, the standard cooler and should be fitted in series (not parallel) with the factory unit to make sure the vehicle’s thermostat can get everything up to operating temperature without too much delay.
Isuzu’s official line is that the D-Max and MU-X are already fitted with a heavy-duty trans cooler from the factory, so no additional hardware should be required. Tranny experts disagree, but the best bet would be to find a fitter that will warranty their work as an aftermarket cooler that failed would almost certainly give Isuzu the option of walking away from any warranty claim.
Those DPF blues. Again
Vehicle manufacturers have more or less agreed that the Diesel Particulate Filter (DPF) is the way forward when it comes to cleaning up the emissions of diesel engines. But the DPF has a problem, and it’s one that affects not only the Isuzu models we’re talking about here, but pretty much all vehicles that use the technology.
That problem becomes a bit more understandable when you consider the front-bar names for a DPF; soot filter or soot trap. Yep, the DPF’s role in life is to trap some of the harmful emissions, store them and then burn them off at a later date. Why doesn’t it just burn them off and turn them to ash in real-time? Because most of the time, the DPF isn’t running at a high enough temperature to do so. And there’s the second part of the problem.
Until you get the engine and exhaust system hot enough for the burn-off to occur, it won’t (can’t) happen. So, if all you do is lurch about the city and suburbs in your D-Max or MU-X, pretty soon the DPF will be full of soot, the warning light will appear on the dashboard and you’re up for the not insignificant cost of having the filter manually cleaned. Or replaced, if you’ve been really unlucky.
Sometimes a good run down a road at a decent speed will be enough to get the engine hot enough to allow the DPF to burn off. Other times it won’t be, which is when you have to take a deep breath and front up at a workshop to have the filter either manually cleaned or, in extreme cases, replaced outright.
What’s that tapping noise?
The Isuzu 3.0-litre turbo-diesel doesn’t have hydraulic valve-lash adjustment, so checking and setting the valve clearances is a routine maintenance job. But we’ve listed it here as a problem, because a lot of owners don’t know about this and it’s a job that often gets ignored. That’s the bad news. The good news is that the adjustment is via screw-and-locknuts, rather than the vastly more fiddly and difficult shim-and-bucket design. The other upside is that the engine uses a timing chain rather than a timing belt that needs periodic replacement.
You’ll be able to identify poor valve adjustment by a ticking noise from the top of the engine that is usually worst on cold start-ups. That’s if the valve clearances are loose, of course. If the valves are tight, you won’t hear a thing but the top end of your engine will be copping a hammering. Long term, you could easily damage the valve stems with loose clearances or damage a cylinder with not enough (tight) clearance.
Treat checking – and adjusting if necessary – valve clearances as a once-every-40,000km routine job. Make sure you fit new injector seals and a rocker-cover gasket at the same time, too, as only the greatest optimist in the world would ever re-use a gasket and think it won’t leak. Be sure not to over-tighten the rocker-cover (or it’ll crack) and make sure any grots that fall into the engine as you remove the rocker cover are picked out and not left to cause mayhem in the diesel’s upper-cylinder area.
The biggest modification you can make to avoid the DPF becoming clogged is to modify your driving patterns. Make sure you take the old girl for a half-hour strop up a freeway at freeway speeds (not sitting in gridlock like most freeways) every month or so, That gives the exhaust system (and the DPF) the chance to get hot enough to do its regeneration thing and save you all those headaches.
Some geniuses will also tell you to bypass the DPF altogether. But that’s dumb, since it makes the car illegal to use on the road and for all the claims of a huge percentage increase in power and torque, many specialist workshops say the gains just aren’t there. That said, you can buy a kit that deletes the DPF but take it from us, its strictly for competition, non-road-going cars. And ironically, a competition car that is driven flat out everywhere is one that wouldn’t have DPF problems in the first place.
There’s really nothing you can do to get around this maintenance chore. Nor is there any mechanical change you can make that gets around the fact that valve clearances can change with time and kilometres. However, we’ve never heard anybody blowing a motor to bits through servicing the engine regularly and treating it with some respect.
Front-wheel bearing wear
When you think about the life led by an off-road four-wheel-drive, it’s a wonder they last any time at all. In the case of the Isuzus, many owners have found that front bearing life is sometimes less than 50,000km. The problem there is that many of them only find out when they have new tyres fitted and the tyre shop phones to say that the wheel alignment can’t be done because there’s too much play in the wheel bearings. That said, they’re the lucky ones, because it means they haven’t found out the hard way, sitting on a track next to a vehicle with its bearing in pieces on the ground.
Again, this is not a problem unique to Isuzus but it is one that can’t be ignored. But then, it doesn’t have to be if you make it part of your regular maintenance schedule.
This is a real simple one; have the front wheel bearings inspected and greased or replaced every 30,000km. Always use an appropriate grade and type of grease, remembering that, at some point during the next school holidays, the vehicle will be standing sills-deep in (possibly salt) water.
You can re-pack the bearings yourself if you know how to spot the wear signs, or a workshop can do it pretty cheaply as an add-on to your regular oil change service. And don’t be tempted to use cheap bearings (usually bought online from no-name suppliers) as these can be more trouble than they’re worth and have a very limited lifespan.
Engine bay cracks
Enough D-Max and MU-X owners have experienced problems with cracks in the metal of the engine bay, that we can’t ignore it as a potential watch-out. It seems the cracks are caused by either stress or metal fatigue and are most likely to show up on the suspension towers, near the VIN plate or low down on the inner guards.
Chassis have been cracked , too, mainly at the front where big, heavy bull-bars and winches have been fitted, effectively cantilevering off the rails. It seems as though the way the Isuzu chassis is constructed allows for the front rails to flex and that, in turn allows the bulbar to `rock’ from side to side, magnifying the metal-stressing effects.
The only 100% foolproof, legal way to fix the cracks in the engine-bay sheet-metal involves replacing those parts of the bodyshell structure. Not cheap, and definitely not easy. In fact, it’s a big bodywork deal in most cases.
Yes, you can weld the cracks up but at that point, you’re technically altering the crash signature of the structure and that’s kind of a no-no when it comes to the way the car performs in a shunt. It could alter the way the air-bags work, too, but then so does fitting a big bulbar. That said, we know which way most owners will go.
As for the front rails, the best advice is to use the lightest bull-bar that will still do the job and think about where you mount a winch.
When you re-grease bearings, remember that unless you have have a small bead of grease forming at the seal, the bearings are probably not full of grease. You can also extend bearing life by letting your vehicle (and the hot wheel bearings) cool down before plunging into a cold creek or river. The thermal shock involved in not doing this can make the bearings take a big gulp of water, rather than the seals keeping it out.
Instead of plonking a winch way out front where it has the maximum leverage on the chassis members, it might be better to mount it back towards the front axle, maybe on a cradle that bolts between the rails (as if you were using an alloy bull-bar). That way, you’ve taken a huge amount of stress off the rails and that’s got to be good news. That said, our experts reckon there’s a limit to this before the winch gets in the way of the air-con condenser and everything else at the front of the engine bay.
Be careful where you mount a second battery, too, as the extra mass of a big battery could easily lead to the sort of engine-bay cracks reported. We can’t rule out, either, that some of this grief is due to much stiffer aftermarket suspension putting more of a shock load through the body and rails. Be careful how high and how stiff you go when lifting or attempting to improve the load carrying of an Isuzu (or any other make and model) and be careful how radical you go suspension-wise.