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The 2022 Toyota Land Cruiser 300 Series' new V6 diesel still has big question marks hanging over it | Opinion

The LC300 will enter Australian showrooms in the fourth quarter of this year.

An all-new engine is a big deal for any manufacturer.

But when it’s an all-new design for an off-roader destined for the Australian outback, then the in-service success or otherwise of the design takes on even greater importance for the future of the model.

Ands when that model is the legendary Toyota LandCruiser, well, the much-discussed new twin-turbo V6 had better be sorted from day one.

Obviously, Toyota tells a pretty rosy – if brief, at this point - story when it comes to the V6 in question: “A newly developed 3.3-litre twin-turbo V6 diesel engine achieves V8-beating performance and flexibility, lifting power output to 227kW (+13.5 per cent) and torque to 700Nm (+7.7 per cent).”

Fair enough, but what about durability in the long term and reliability in the short term?

Just as heads were scratched when the previous LandCruiser 200 Series was launched back in 2008 - with its diesel V8 engine sporting both crucial electronics and its starter motor in the vee of the engine - the novel layout of the new V6 is also raising eyebrows.

Specifically, the question marks hang over the engine’s `hot-vee’ or `hot-side-in’ layout which places the exhaust manifolds inside the vee and the intake manifolds on the outside; the opposite to conventional vee-engine architecture.

It’s easy to see why Toyota has chosen this layout; the placement of the exhaust manifold in the vee allows the turbocharger units to be mounted physically closer to the exhaust ports, making the turbos more efficient and reducing turbo lag.

Higher turbo-outlet temperatures also allow catalytic converters to light off faster in the case of a petrol engine.

The hot-vee layout also makes the engine physically less bulky, although, in the context of a 2.5-tonne station-wagon, that’s possibly not Toyota’s main motivator (although it does create more room for an off-roader’s more complex driveline, remembering that hybrid 300 Series Cruisers are expected eventually).

But as any engineer will tell you, there’s never a free kick. And in the case of a hot-vee engine, the price to pay involves a big step-up in underbonnet heat management.

In a conventional vee engine, the turbochargers are placed beside the engine, with lots of cooling air around them. In some cases, they can even be mounted lower in the engine bay for even more air-flow (although that’s not usually the case with an off-road vehicle designed to ford rivers).

But in a hot-vee design, they’re sandwiched between the cylinder heads, manifolds, firewall and finally, the vehicle’s bonnet. In fact, all the hottest bits of the engine are grouped tightly together in a ready-made pizza oven.

To make matters worse, the bonnet on a hot-vee engine requires a heat shield (to prevent the paint peeling from heat), and that simply reflects the heat back into the vee it was trying to escape. So, heat management becomes the new game.

And intuition suggests that a 2.5-tonne off-roader crossing a hundred kilometres of sand dunes in low-range, with deflated (for traction) tyres, in 40-degree ambient heat might test the best heat-management strategies.

Doubtless the new Toyota will have protection measures to prevent a total meltdown, but having a vehicle go into limp-home mode half way across the Simpson Desert would still be deemed unacceptable to most Aussie off-roaders.

Toyota has yet to reveal the exact technical details of the new LandCruiser, including the layout and specifications of the cooling system.

Given the brand’s experience with hot climates, however, there’s no doubt plenty of testing and certification has taken place.

It’s also worth delving into BMW’s heat-management measures in cars like it’s current-model M5. That’s because the Bavarian brand was the first to introduce a production car with a hot-side-in petrol engine; the 2008 twin-turbocharged N63 V8.

Even with the brand’s full development program, technical updates over the years have seen the basic N63 engine’s cooling system revised with the addition of a second coolant pump in 2012 and, for 2018, a revised radiator system and improved thermal shielding for the crankcase and cylinder heads.

BMW’s current M5 uses the S63 bi-turbo V8 which also uses hot-side-in technology and has raised the bar again in terms of cooling.

For the 2021 model, the M5 uses two radiators – one low and one high temperature – and there’s an engine-oil cooler under the car. The low-temperature radiator features two electric coolant pumps to help maintain the performance of the engine’s intercoolers.

The high- and low-temperature radiators only cool the engine and turbocharger bearings, the intercoolers for the intake air are separate units. The transmission itself is cooled by a pair of coolers mounted low at the front of the car

The high-temp cooling circuit, meanwhile, uses a mechanical coolant pump as well as an electric coolant pump to continue coolant flow around the turbos’ bearings after the engine has stopped.

Of course, BMW’s experience has been in road-going cars, not (despite what BMW’s marketing department tells us about the X5 and X6) off-roaders. That said, those road cars are of the flat-out-on-the-autobahn variety, not sand-dune crawlers.

But it seems some fairly heavy-duty commercial vehicles aren’t scared of the hot-vee layout either: Ford in 2010 introduced the 6.7-litre `Scorpion’ variant of is Power Stroke diesel V8 range with just such a layout.

And while that engine has had its issues Stateside (mainly fuel-injection pump failures and EGR failures), it’s the Scorpion’s radiator and inlet-manifold coolant inlet failures (causing coolant leaks) that should be ringing the loudest alarm bells in this context.

How Toyota’s strategy for the 300 Series compares with other production engines with the same architecture remains to be seen, but it’s a fair bet all eyes will be on the first 300 to tackle the Simpson Desert in summer.

Again, there’s no reason to doubt Toyota’s commitment to development and testing, but until we have the details of how and where the new Cruiser was developed and certified, Aussie off-roaders and those who tow big loads will be watching keenly.