Isuzu 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.

The first thing to check is the fluid level in the transmission. Consult the owner’s manual for the correct method of doing this (sometimes the engine needs to be running and the transmission at operating temperature, in other vehicles everything needs to be cold, so this is important).

Low transmission fluid can cause all sorts of problems with gear selection, flaring between gears and actually making the vehicle drive, so that’s why this is the first step. If the level (and the condition) of the fluid is fine, then you need to start looking deeper, and a transmissions specialist is probably your best bet there.

The transmission is a sealed system, so any drop in the fluid level suggests a leak somewhere that needs to be fixed or the problem will return.

Beyond that, running a transmission that isn’t behaving properly can cause damage to the unit itself, so continuing to drive the vehicle in this state is not a good idea.

Even though your caravan is not at the towing limit of your vehicle, more than 2000kg still puts a pretty big load on the Isuzu’s engine. And that, simply, put, is why it’s using its gearbox to keep the engine happy and revving at the appropriate speed to safely make the power and torque you require to move that caravan at highway speeds.

The short answer is that you won’t be hurting the engine by allowing the gearbox to determine what gear it needs to be in. Quite the contrary, and over-riding the transmission to force the vehicle into a too-high gear would, indeed, damage things by overloading various components.

Short of fitting a more powerful engine, there’s not a lot you can do about this. After all, you’ve taken a two-and-a-bit tonne vehicle and more than doubled its weight (with the caravan) meaning you’re asking it to do twice as much work with the same engine. Fundamentally, you can’t beat physics.

The minimum recommended tyre pressure for your car is 230kPa. That’s equal to about 34psi in the old money. Bear in mind that’s the minimum Isuzu recommends. So 210kPa is definitely too low.

But don’t be tempted to use the tyre’s appearance as a guide to it inflation pressure. Most time, you won’t visually pick a deflated tyre until it reaches below 20psi, at which point it’s already dangerously low. Even parking on a sloped piece of road can make a tyre look underinflated thanks to the weight of the vehicle distorting the tyre’s sidewall.

Using 230kPa is the minimum, you’d definitely increase pressure if you were towing a trailer, were fully loaded or travelling at freeway speeds on a hot day. And don’t be too trusting of your tyre gauge if it’s throwing up low readings all the time. Check it against another gauge to see if there’s a discrepancy. And don’t be at all be tempted to trust the tyre pressure gauge at a service station. The modern, automated tyre inflaters are better, but the old hand-held ones are constantly left out in the weather, thrown on the ground and run over by fuel tankers.

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.

You’ve kind of already answered your own question by saying that you’ve already waited a year for delivery. Saying no to this one and ordering another might see a similar delay and you’d be back to square one. And a year older. Like many brands, Isuzu deliveries were adversely affected by global supply-chain problems and the world shortage of silicon-chips needed to make on-board computers work.

There are two issues with a car with last year’s build date. The first of these is that the motor trade uses the year of manufacture when calculating retained (trade-in) value. So, if you don’t plan to keep the car long before trading it in, then maybe that’s a concern. If you plan to keep it for 10 years or so, then an extra birthday will have very little affect on its trade-in value by then. This is something you might be able to negotiate on with the dealership you’ve purchased from

As for warranty, Australian Consumer Law states that motor vehicle warranties start form the date of first registration, not the build date. So even though the car might technically be six months old when you get it, the factory six-year/150,000km warranty will start from the day it’s delivered to you as a brand-new vehicle. The exception to this is if the car was originally a dealer demonstrator, when the warranty would start form the time it was registered by the dealership. If that’s the case, this should be reflected in the purchase price as it’s no longer a brand-new car you’re buying.

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.

It's true that new engines can be 'tight' and this can lead to higher fuel consumption than they achieve with a few more miles on board. And since you're almost at the 30,000km mark now, why not try the dealer's advice and see if things start to improve.

The MU-X was never the most fuel efficient vehicle in its class, but even so, 12.2 litres per 100km on the highway sounds a little excessive (although not as much as you might think). I'd expect this vehicle to return highway fuel economy figures closer to 10 litres per 100km or maybe a bit less.

However, there are several factors that might be skewing your results. The bluff aerodynamics of a vehicle like the MU-X mean that even a slight headwind can increase consumption. So can the addition of accessories such as a bull-bar and roof racks. A set of roof racks on their own can add a litre of fuel to every 100km travelled, and that's if they're not loaded. Throw a spare tyre and some gear up there and it's even worse.

Bigger (taller) tyres can also increase fuel consumption, and so can running your tyres at too low a pressure.

This needs to be sorted out quickly as a car that you can't be sure is in Park is always a potential to roll away on its own causing who knows what grief and damage. It sounds like there's something amiss with the way the gear selector is talking to the actual transmission, and any resistance in the action of the shifter really shouldn't be there. That said, you do need to have your foot on the brake to select a gear from Park, so maybe you're taking your foot off the brake pedal prematurely.

You're possibly correct that the two issues are related as a car that thinks it's not in Park, will probably not want to allow you to use the walk-away locking mode. But here's the good news: This is absolutely a warranty issue and Isuzu needs to fix it at its cost.

Book the car in to be inspected as soon as possible and, in the meantime, make sure it's parked somewhere from which it can't roll away. Physically chocking a wheel (with a house-brick, a rock or whatever) isn't a bad idea till it's fixed, either.

This sounds like a case of low transmission fluid. Check the transmission dipstick according to the instructions in the owner's manual to see if the level is where it should be. Low fluid level can cause all sort of problems from slipping to a lack of drive to uneven shifts and shifts occurring when they shouldn't. Also, try to find out what fluid was put in the transmission when it was last serviced. The wrong type or grade of fluid can cause the same types of problems as not enough fluid.

If the fluid checks out, then you need to start looking at other causes such as glitches in the on-board computer that controls the driveline. An electronic scan of the vehicle would be the next step.