The BMW 8-Series Works So Much Better With A Diesel Engine

The straight-six diesel in the 840d is a much better fit than the M850i's V8, and not just because of the economy potential

Although you’ve come here to read about the 3.0-litre straight-six diesel version of the new BMW 8-series, I’m going to start by talking about the Mitsubishi Outlander. Yes, really.

Not because I took some strong substances before opening my laptop. No: it’s because the Outlander is a great example of the tide turning against diesel. When talking to Rob Lindley - Mitsubishi UK’s MD - at the Geneva Motor Show, he mentioned that Mitsubishi has actually stopped importing the sole oil-burning version of the vehicle, so once stocks are depleted, you’ll only be able to have it as either a plug-in hybrid or petrol.

That would have been unthinkable a few years ago, wouldn’t it? We’re used to big, heavy SUVs only being available with diesel engines, not the other way around. And yet here we are. The Outlander is just one example of diesel demand spectacularly crashing, hastening the demise of thusly fuelled cars amid the rise of electrification.

BMW - The BMW 8-Series Works So Much Better With A Diesel Engine - Features

It’s a shame as in some contexts, a diesel engine still makes so much sense. Take the BMW 8-series as an example. Certainly, I loved the M850i we tried earlier in the year. But the shouty, brawny nature of the twin-turbo V8 did often seem at odds with the 8er’s general characteristics - it’s a soft, wafty GT car which, though plenty capable thanks to its trick all-wheel drive system, feels at its most comfortable when cruising.

Sticking a 523bhp, 4.4-litre engine into the mix is surely like dropping a bunch of scotch bonnet chillis into a Lancashire hotpot. Interesting, of course, but the two things don’t really go together.

BMW - The BMW 8-Series Works So Much Better With A Diesel Engine - Features

The straight-six twin-turbo diesel, though, is much more like it. You lose the V8 theatrics, but the quiet, reasonably refined 3.0-litre fits with the 8-series’ wafty nature so much better. The slick eight-speed ZF automatic gearbox - the use of which BMW has mastered more than anyone else - makes the most of the narrower powerband, ensuring fast progress is always effortless.

And the progress is indeed fast: it’ll manage 0-62mph from a standstill in 4.9 seconds, and while that’s well over a second off the V8, it’s not exactly slow, is it? Despite the pace, it’s still a very light drinker - 50mpg on a run is easily achievable, giving you a potential range well beyond 500 miles. In the M850i, you’ll struggle to get it into the high 20s even if you’re only tickling the throttle.

BMW - The BMW 8-Series Works So Much Better With A Diesel Engine - Features

In terms of the way it goes around corners, it’s all pretty similar to the M850i, even though the 840d’s setup is softer still. It’s still awfully keen to send lots of power to the rear, it leans but not excessively so, and you sometimes get a little dose of understeer in tighter corners to remind you that this is a near-two-tonne car. The steering’s decent rather than remarkable, and you’re best off avoiding its overly-heavy ‘sport’ mode.

It’s a fun car to drive fast, just clearly not something that’s trying to be a sports car. And in the absence of a big petrol engine, this is a lot easier to get on board with.

BMW - The BMW 8-Series Works So Much Better With A Diesel Engine - Features

The final big argument for the 840d is price: at £76,270 it’s nearly £25,000 cheaper. Is the M850i worth a third more? I’m not so sure.

It’s a lot easier to recommend, even if at £76,270 the interior still isn’t quite as special as you might like. But how about for me? I’m certain that the 840d is the pick of the two 8ers. Completely convinced. Without a doubt. So of course, if it was my money, I’d buy the V8.