Diesel Buyer's Guide: How to buy, own and maintain a modern diesel engine

Modern diesel engines are efficient and powerful. But can you give it what it needs? Here’s your definitive dummy’s guide to owning a new diesel…

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The diesel engine has come lightyears. It’s no longer considered a lump of agricultural pig-iron designed to move heaven and earth, or simply to plough it. In many respects, it’s the superior powertrain.

In the last 10 years, the diesel engine has become a premium option, offering more power, increased thermal efficiency and greater fuel economy.

But despite diesel technology’s improvements, and Volkswagen trying very hard indeed to smear its reputation thanks to gross corporate misconduct at the highest level, and poor reliability thanks to Toyota’s underdone R&D in recent years (which is fixed now, apparently), the diesel engine still has many benefits to offer.

If you want to understand the anatomy of a modern diesel, here’s my deep-dive into how diesel engines work >>

Diesels are more efficient than petrol, by a long shot. The compression is higher, allowing the expansion to take place over a greater range, which delivers a huge boost in thermal efficiency. Meaning: Less CO2 for any given driving.

If you’re in the market for a dual-cab ute, large seven-seat SUV or a hardcore 4x4 off-road wagon, you should make it your goal to understand the nuances of the modern diesel engine.

Doing this will keep you out of the service department and happily driving your family to and from the compulsory social events your kids and spouse have meticulously planned for you over the next five years. The ones you can’t get out of.

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BUYING

Shopping for a dual-cab ute like the Mitsubishi Triton, Mazda BT-50 or Ford Ranger, a 4x4 wagon like Mitsubishi Pajero Sport or Toyota LandCruiser or in the large seven-seat SUV segment for a Kia Sorento, Hyundai Santa Fe, Mitsubishi Outlander - or possibly even a people mover like the Kia Carnival - then you’re going to have to live with diesel.

Which means you need to know if the petrol alternative is a better option for the majority of your driving situations.

Does 90 per cent of your driving occur in stop-start commuting traffic in one of Australia’s capital cities? Are you based in the outer suburbs or a regional city or town where freeways or rural B-roads are the staple? Perhaps you work alternative hours and frequently use major arterial roads when they’re mostly free-flowing, and you don’t encounter stop-start traffic all that much.

This needs to be part of your thought process before deciding between diesel and petrol.

Most modern diesels, especially from the brands I routinely recommend, are pretty reliable. I don’t get many complaints, if any, from the likes of Hyundai and Kia, Mitsubishi or Mazda - generally.

But they come with a caveat to ownership. You have to be prepared to give the diesel particle filter (DPF) the sufficient amount of sustained highway driving in order to do its mad regeneration voodoo. This shouldn’t be an inhibitor to you buying one, because the benefits of modern diesel ownership - if the shoe fits - are significant. Don’t be put-off by a DPF and the diesel engine it’s attached to, just keep this in mind as one of your ownership routines.

It’s like owning a dog. You have to feed it, water it, talk to it, and exercise it. Your modern diesel needs to be taken for a substantial walk every now and then, so it doesn’t emphatically shit itself and foot you a repair bill with three zeros on the end, maybe even a comma in there.

That’s not to say it will go poop in its DPF trousers, but this will mitigate against the risk of it happening.

When you take your potential next diesel for a test drive, propose taking it through a range of different driving situations where possible. Try it in traffic, on the freeway, try low-speed manoeuvres and do plenty of tasks which require a variety of throttle positions to see if you can deal with the nuances of throttle management.

Here is a cheat sheet of what I regard as the best diesel engines on the market, for their reliability, their performance, and the overall vehicle they’re packaged with.

Hyundai-Kia 2.2L

Available in the Hyundai Santa Fe and Kia Sorento, the 2.2L makes 148kW peak power at 3800rpm and 440Nm from 1750-2750RPM. Sorento GT-Line off this engine with a power-to-weight ratio of 77.6 - not as much outright as the Mazda CX-9 or Toyota Kluger, but they have to rev to 5000 or 6000 rpm to reach peak power.

This is one of the best diesels on the market right now. It makes more power than the new Isuzu D-Max (albeit 200 revs higher), but importantly, it’s also 19kg lighter than the old Sorento thanks to an aluminium block. Delivers hybrid-like fuel economy - 6.1 litres per 100km on the official combined cycle lab test, and 5.3 on the highway.

Coupled to the new eight-speed dual-clutch where, slowly accelerating from standstill, I can’t actually pick the point at which the automated clutch engages, it’s a great powertrain with great reliability.

Upcoming new Kia Carnival and Hyundai’s full-size Palisade SUV will also get the 2.2.

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Mitsubishi 2.4-litre

This engine is shared in the Triton ute and Pajero Sport.

An aluminium block like the Hyundai-Kia 2.2, its outright power output isn’t as macho as most of the ute crowd but makes up for that having, in my view, the best off-road transmission. And that’s really why you buy one of these things, right?

Peak power is 133kW from 3500RPM and 430Nm of peak torque from just 2500RPM. In GLS spec, Triton has a power to weight ratio of 66.8kW/t, which isn’t as macho as say a Ranger Wildtrak 3.2 or Volkswagen Amarok, but the VW is a safety shitbox and the Ranger, whilst a pretty robust powertrain overall, it doesn’t come with particularly good support from Ford. Mitsubishi’s 2.4 has a compression ratio of 15.5:1 and is reasonably relaxed under load, unlike the Ranger 2.2.

Pajero Sport offers the same power figures but gets Mitsubishi’s eight-speed Super Select II transmission which is ideal for heavy towing up to 3.1 tonnes (although I always advise against pushing that limit in a 2.2-tonne vehicle).

Triton and Pajero Sport also get independent transmission oil coolers for improved ventilation of the transfer case, which Ranger and Hilux don’t.

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Toyota LandCruiser 4.5L

This enormous twin-turbo V8 diesel is the higher-tuned version of the single-turbo V8 dinosaur heart in the LandCruiser TroopCarrier which drinks fuel like Barney Gumble left alone with a beer tap. The TT V8 makes 32.5% more peak power, 51% more peak torque and returns slightly better fuel economy - despite being in a platform weighing 500kg more; 200kW peak power from 3600RPM and 650Nm peak torque from 1600-2600RPM.

But this engine is due to be phased out with the next iteration of the LandCruiser, dubbed the 300 Series, expected sometime in 2021. The TT V8 is a monster of an engine in modern terms, offering a 74.9kW/t power-to-weight ratio in the $130k Sahara, and a compression ratio of 16.8:1 - better than the Triton/Pajero Sport, but significantly more expensive. I have also had reports over the years of dusting problems with red dust being sucked into the air intake during outback adventures.

If you tow moderately heavy loads fairly regularly, like a caravan or horse float, the 200 Series is decent, but overkill. It certainly has the grunt to pull it, but I think you’re wasting money performing the same task which could’ve been done by a Pajero Sport, or even a Nissan Patrol.

There is also a bunch of buyers out there with zero intention of taking their LandCruiser anywhere near the open road or, heaven forbid, a dirt road. And that’s fine, it is a very civilised urban-assault vehicle. Although, this demographic needs to be aware of the whole DPF-care aspect of ownership - although I doubt many are.

Toyota 2.8L

Thanks to Toyota Australia finally installing a manual DPF regeneration switch to its Prado, Fortuner and Hilux 2.8-litre models, this particular diesel engine has proven relatively reliable. Who would’ve thought, the Hilux wasn’t unbreakable after all.

It’s not the most powerful, and not the least. But having one means handing over thousands more. You get 150kW peak power (up 20kW recently) from 3400RPM and 500Nm peak torque at 1600-2800RPM, which is better than the previous versions. The Rugged X comes with a bunch of off-road gear from the dealership, but you have to question the cost effectiveness of this.

While the Toyota 2.8 has proven somewhat reliable in the last two years thanks to the manual DPF switch, it did take Toyota Australia far too long and too many cease-and-desist letters to the likes of Berrima Diesel about discussing their precious Hilux’s deficiencies.

I don’t hate the Hilux, it’s an okay vehicle in many respects, but it’s quite expensive and sells as popularly as it does, as far as I can tell, because of the badge on the front. Toyota has a strong dealer network and are generally good at customer support. People trust Toyota, however mediocre they are (in my opinion) on the product development front.

There’s also the updated Hilux arriving now, which claims to have fixed the DPF’s technical problems which included the dodgy ‘fifth injector’ - but I strongly urge you to wait at least six months to see if that’s true. Toyota has stated publicly that a ten-year warranty extension “applies to customers who may have experienced an issue with the DPF system which may present as substantial white smoke discharged during the regeneration process”.

Or, if you don’t want to be Toyota’s lab rat in 2021, the Triton hasn’t had any DPF problems.

Everything wrong with Australia’s top 10 dual-cab 4X4 utes >>

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Isuzu D-Max 3.0L

Shared with new Mazda BT-50.

This engine is certainly not new, like the motoring media might have you believe. It’s essentially related to the same diesel engine introduced 20 years ago in the Holden Rodeo (remember that?). I don’t buy into the ‘legendary truck’ BS.

The 4JJ-whatever engine is an outdated boat anchor. Use-by date: expired. Reliable: Sure. Out-classed by most competitors: Yep, still. Although, this time around it’s had some semi-serious changes to try and keep you from noticing anything the Joan Rivers reality. Apparently they’ve used a new engine block, cylinder-head, crankshaft and lighter aluminium pistons, and a new air intake system (which now faces forward - how original).

It also uses a new electronic variable geometry turbo, and a new DPF which is apparently lighter and more efficient. As far as I’m aware Isuzu hasn’t had any significant in-service issues with its DPF which does a pretty good job of burning-off on its own. They claim a new dual-mass flywheel also helps reduce the appalling unrefined vibrations the previous model’s drivetrain was infamous for.

Power is adequate. Like, barely: 140kW of peak power at 3600rpm, and 450Nm peak torque from 1600-2600rpm. So it’s basically the same as a Toyota Prado 2.8-litre diesel. Congratulations. D-Max has matched Toyota. Pity Mazda’s SKYACTIV 2.2 diesel in CX-5 and CX-8 also offers 140kW (peak power) and 450Nm (peak torque). With 26 per cent less capacity.

I suspect they wanted to sell on the ‘truck engine’ image, which in my estimation, seems to attract a certain type of blue-singlet buyer. Here’s how to save thousands on the new BT-50 (She-Max) and D-Max >> the His and Hers ute collection. Each sold separately; 12-volt batteries included.

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OWNING

One of the two most important obligations you will have to your shiny new modern diesel engine is keeping the DPF healthy.

This means ensuring that at least once a fortnight you get out on the freeway and drive at about 80-100km/h for a sustained period, about 20-30 minutes. This ensures the DPF gets hot enough to sustain a critical burn process of the carbon nanoparticles which build-up in the exhaust’s filter system.

Here’s what happens during DPF regeneration >> and don’t ever let anybody tell you deleting your DPF or the Exhaust Gas Recirculation (EGR) systems because not only is it illegal, it’ll also kill your warranty, and will probably cause even more problems down the track. EGR makes engines more efficient and it reduces emissions.

The second vital ownership requirement of a modern diesel is routine servicing. This is the case for any petrol engine too, but it’s important to make sure you adhere to the scheduled servicing outlined by the manufacturer. Those servicing intervals are based on time or kilometres driven - whichever occurs first. You cannot push the time just because you haven’t driven much (especially in 2020), because sitting stagnate is also hell on earth for engine oil, which increases water dilution.

This is why you need to strictly adhere to your diesel’s scheduled servicing >>

Not doing so could cost you thousands >>

When or if your DPF warning light comes on, it’s unsettling. So you need to understand what to do in that heart-palpitating moment. If ever your DPF warning light illuminates in your new diesel vehicle, here’s what you do >>

But it’s important to understand the DPF warning light and any problems of this nature can often be the symptom of you not doing enough highway driving to allow the system to perform its burn-off regeneration process.

If you do regularly get out on the highway and allow the DPF to do that regeneration, then you can be pretty confident there’s a problem further upstream of the exhaust system. One common cause is a tiny air leak in the silicone hose at the MAF sensor tricks the computer into thinking it needs to inject more fuel into the cylinder and therefore runs rich and ramps up the blockage problem.

Use a qualified technician who knows what they’re doing to service your DPF: Don’t be scared to ask you local mechanic, and if he/she isn’t confident, ask if they know any reputable, qualified diesel technicians. Ensure they use the correct low-ash oil as required by the manufacturer during servicing: Again, ask, check in the manual, write it down. And confirm they have reset all the appropriate computer settings including the oil dilution reset.

And also remember the owner abuse factor. Owner abuse is how manufacturers dodge warranty claims because DPF abuse is very much part of that. If you have a serious DPF regeneration problem, they will likely fight you by exploiting a case for inadequate driving conditions, forcing you to foot the four or five-figure bill.

If you’re a Monday-to-Friday tradesperson who is on the road by 6am and knocking off in the early to mid-afternoon in order to ‘beat the traffic’ (along with every single other tradie, delivery driver, courier and truck), then you’re going to get the best use out of a diesel.

2020 Ute Market Buyer's Guide >>

You’ll easily satisfy the DPF’s highway requirements, and you’ll get to take advantage of the pliable powertrain and smooth throttle response, especially with equipment in the back of the use and a trailer full of tools. Same goes for vans, which are essentially never free of any load from the moment they leave the dealership.

However, the diesel SUV market has been something of a misnomer over the last decade. Some brands have refused to go diesel or dropped theirs entirely, either as a result of the epic work Volkswagen did to shit on the diesel’s reputation.

When parking your shiny new diesel, which probably has a turbo, you need to be conscious of the turbo too.

If you get to a destination after working hard, putting lots of power down to the ground, climbing hills or towing something heavy, when you get to your destination and you park, give the car about 90 seconds to 2 minutes of idle, in park.

The turbo has been working really hard, turbochargers get really hot because they are powered by hot energetic exhaust flow (about 600-800 degrees) quite close to the exhaust manifold.

Practical engine run-in advice for tradies in utes >>

If you just turn the engine off it’ll cook the oil inside the turbocharger housing. Doing this idle for a couple of minutes will allow water flowing through the water jacket to cool it down, or the oil will continue to circulate and gradually cool down to an acceptable level.

Highway driving generally is pretty low-load for a turbo-diesel, with light throttle inputs and mostly cruising. But if you stop the car, select Park, put on the park brake, get you and the kids ready with the engine on, by the time you’re ready, if you then shut down the engine, you’ll give it a cooling off period.

Lots of straight shutdowns with a hot turbo-diesel over time, with no cooling-off, all those incremental turbo-cooks will gum-up the oil pathways and eventually you’ll be driving, the oil pathway will lock-up and you’ll be up for a multi-thousand dollar repair job.

If you do lots of heavy towing or lots of cold starts, service the engine early from say 12 months to six months for good measure.

UNDERSTANDING DIESEL

There’s absolutely no denying we live and die by our vehicles, whether it’s the tradie work ute or family SUV, our lives are emphatically less shit thanks to the seemingly infinite mobility a modern diesel engine offers.

But not all modern diesel engines are equal and not all brands offer you the same level of customer care and support - yeah, I’m looking at you, Land Rover, among others.

If you are strictly an urban dweller, who drives ten minutes in built up traffic just to do the return shopping trip, then I’d suggest you need to be careful about which car you buy. Sitting in commuter traffic four out of five days per week, with little or no highway driving, is a good recipe for a shit sandwich if you buy the wrong vehicle.

I have a Lemon List for a reason, because there are brands out there whose commitment to you is about as solid as Trump’s altruism.

But if you buy your diesel and treat it with the due care it requires, you’ll reap the benefits of both an efficient and effective powertrain that is good on fuel, but also one that has a wide variety of applications.

Diesels are better for towing due to their tendency to be more predictable and linear in their power delivery, as opposed to petrols which are more prone to spiking revs and having to be worked harder to achieve similar acceleration and power delivery as the smoother diesel.

When you’re off-roading, the gradual power delivery of a diesel engine means you can modulate the throttle better in soft sand or slippery terrain when you need to be gentle. A petrol engine, like a shitbox Jeep Wrangler or something would spin its wheels.

If you’re in the market for a new vehicle and a diesel is on your list, I urge you to think about what the vast majority of your driving is going to consist of. Ask yourself what you want the vehicle to do and asses, honestly, if you can respect the needs of a DPF.

You also need to be regimented with your servicing if you’re going to be a regular heavy tower, or if you plan to take your diesel off-road frequently. You might even want to consider long-term intermittent servicing if you have extreme use in mind.

Modern diesels are far from the noisy, dirty shitboxes which were only ever used by old Land Rovers and tractors. They’re full of brilliant engineering, are very precise and economical.

The weakest link in the diesel’s ownership chain is the human who buys it. Love your diesel and it’ll love you back - in an entirely plutonic way, of course.

If you have any specific questions relating to your diesel purchase, or you want advice on which one to buy, you can email me directly and I’ll give it to you straight.

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