Isuzu D-Max Problems

This sounds like a rear differential problem. The differential is designed to allow the inside and outside wheel of that axle to rotate at different speeds (which they need to do as the inside wheel describes a smaller arc than the outside wheel in a corner). If something goes wrong inside the differential, that function can be lost and the wheels try to turn at the same speed in corners. When that happens, the rear end will skip and jump about as the two rear wheels effectively fight each other.

Limited-slip differentials (LSD) often have this problem when the clutches that control the amount of lock-up in the differential fail or become worn. At that point, similar jumping and clunking noises can be felt and heard. In some cases, a limited-slip differential can be restored to health with a change of fluid and perhaps an additive, but in other cases, the unit must be rebuilt.

The rear differential in your D-Max should be the limited-slip type, but around this time, Isuzu made the LSD an option, so it would be worth checking. If it’s an LSD, a fluid change would be the first step towards sorting this problem.

Isuzu lifted the warranty on its vehicles to six years/150,000km for all utes sold after May 1, 2019. Unfortunately, it sounds like your car was on the road in 2018, which means it was covered by a five-year/130,000km warranty. Although you haven’t yet covered 130,000km, the vehicle is more than those five years old so, technically, the problem is not covered by warranty.

However, I think it would be worthwhile contacting Isuzu Australia’s customer service division and pointing out the car’s service history and its mileage. Isuzu may then decide to help with the cost of repairs on a pro-rata basis given the circumstances. It is not obliged to, of course, but it’s definitely worth asking.

Sandy conditions are incredibly hard on every aspect of a four-wheel-drive. The sand itself constantly shifts under the tyres and clings to them as well, dragging them down and making the engine and transmission work very hard to maintain progress. You may have already noticed that you use a lot more fuel in sandy country and it’s all because you need to be constantly making more power to maintain speed than in normal conditions. Turbocharged engines and automatic transmissions, in particular, can get very hot very quickly in sand.

With that in mind, it’s very possible that something in the driveline got hot enough for the car’s computer to go into limp home mode to protect what ever was hot from damage. Limp home mode often involves limiting engine revs and turbo boost, both of which contribute to heat production. This would explain why the car would not climb a crest but came good after a break.

A bit of sweating around the various parts of an engine where one component joins another is definitely not uncommon and not really a problem provided it's not actually dropping oil on the ground (at which point it's a leak, not a sweat-mark). But really, an almost-new vehicle like yours shouldn't be doing this at all.

The rear-main seal on the crankshaft is a likely culprit and a common source of leaks from this area, but since it's a big job (gearbox removal) to do it, I can understand why a mechanic would declare it okay and not to worry. The problem with that is that the sweating is likely to become a leak sometime down the track, at which point you'll have to act.

The good news is that because you've flagged this problem with Isuzu while the vehicle is still under warranty, it's called a pre-existing condition and is covered by the factory warranty, even if that warranty has since expired. However, one would hope that Isuzu does the right thing in the meantime and changes the offending gasket or seal to fix the problem.

Be very wary, however, about Isuzu (or more likely the dealer) claiming the problem is being caused by the catch-can you have had fitted. A good quality catch-can, with a relief valve and correct installation should not cause a rear main seal to leak. As for changing the grade of oil you're using, I doubt that it would do much, but since the alternative is a slightly thicker oil, it might just make the difference you're chasing.

Problems like these are hard to diagnose remotely, as there's a lot going on in a modern gearbox. But, conventional wisdom suggests that a noise followed by a series of failures of the same component (the oil seal) means something inside is bent or damaged.

The noise is potentially being caused by something misaligned and rubbing or a damaged bearing, and the blown oil seal is the eventual result of the damage/swarf/heat/friction that results. The other possibility is that the rear gearbox seal is being destroyed from the other end of things, as in the tailshaft. A bent tailshaft could set up harmonics, friction or vibrations that could kill the seal, but you'd imagine there'd be a vibration through the whole vehicle at speed if this was the case.

Your vehicle is under warranty (six years of it from new) so make sure the dealer is aware of the problem and their obligation to fix it.

If we’re talking about the current model D-Max and BT-50, then yes, the entire driveline should be interchangeable. Under the skin, both the Mazda and Isuzu utes are the same vehicle. Car makers enter into joint ventures like the development of this pair of vehicles to keep costs down by sharing the expense of developing, engineering and testing parts like engines, transmissions and, of course, drive-shafts and CV joints.

While most joint ventures like this one will arrive at two vehicles with some visual differences and usually some details differences inside, when it comes to the oily bits, making specific driveline or suspension parts for one vehicle over the other is defeating the purpose of the joint venture in the first place.

Remapping an engine – done right – can provide you with more performance. But there’s also often a price to be paid in terms of reduced fuel economy and increased tailpipe emissions. Typically, there are workshops that are very good at this and others that aren’t so expert at extracting more performance.

But before you go down that route, it sounds like there’s something wrong with your vehicle in its current state. Fundamentally, a 2013 Isuzu D-Max should be able to haul a van of that mass, comfortably at the legal speed limit. That said, that’s a fairly hefty caravan and experience shows that many owners of similar rigs find that about 90km/h is a more comfortable speed for highway travel. So maybe you need to lower your expectations a little.

A full service and tune-up would be the first step in improving the towing situation, by returning all the engine’s settings to their stock position. Modern turbo-diesels can also suffer a fall-off in performance over time as the fuel system (pumps and injectors) wear, the diesel particulate filter becomes full of soot and the intake system becomes clogged with a mixture of soot and oil from the vehicle’s emission-control system. Those are the things we’d check first before shelling out for a remapped engine computer.

Isuzu switched to a new, Euro 5-compliant engine for the D-Max ute in 2017. To meet the stricter Euro 5 emissions requirements, a DPF was fitted. But D-Maxes before that time do not have a DPF fitted. On that basis, your car will not have a DPF.

Given the problems experienced by owners of DPF-equipped vehicles (not just Isuzus) this is one of the things that has made the older D-Max such a popular second-hand buy.

Almost certainly not. Unless there’s some strange quirk of manufacturing that allows the mounting points to magically line up, the current Isuzu D-Max is an all-new design, compared even to the most recent predecessor, let alone the model from 2006. The 2006 D-Max shared a lot of its architecture and engineering with the Holden Rodeo and later Colorado, while the new D-Max is a joint venture with Mazda and forms the basis of that company’s BT-50 range of utes.

You may be able to engineer a set of adaptors to mount the early nudge-bar to the later vehicle, but at some point it’ll get messy and simply not worth the time and money investment compared with buying a nudge-bar designed specifically for a 2021 D-Max. There’s also the issue of whether the old nudge-bar design would be compatible with the air-bag system of the new Isuzu. Again, almost certainly not is the short answer.