The BMW X3 M40d isn't a full M car but it's a full-on performance SUV that's also a remarkably frugal electrified diesel-engined family conveyance. Sixty mph flashes by in under 5 seconds and on a twisting country road, that hot hatch rapidly receding in your rear view mirror will get a bit of a shock. 340hp beneath the bonnet will do that for you.
BMW's famous M motorsport division makes a full Motorsport-tuned version of their X3 mid-sized SUV. This isn't it. This X3 M40d variant is instead, an uber-fast and potentially rather desirable performance version of the standard model, most recently updated with the Munich maker's efficient 48V mild hybrid tech and a series of visual, cabin and media updates. If you don't naturally equate the word 'performance' with 'diesel', then you'll need a mental reset here because the M40d really is very fast indeed, yet it's capable of reasonably frugal returns, even if you give in to the urge of regularly thrashing its 340hp 3.0-litre straight six engine about. Only Audi's SQ5 TDI can rival this combination in this class. But this M40d claims to be a sharper driver's device. Is it? Time to find out.
We've seen this M40d model's 'B57' M Performance twin turbo 3.0-litre straight six cylinder engine before in various black pump BMWs mated, as here, to xDrive 4WD and an 8-speed paddleshift auto transmission: there's lots to like about it. Power output is a healthy 340hp and there's a healthy 700Nm of torque that you can access from as low as 1,750rpm, so when you put your right foot down, this car simply storms towards the horizon. The 62mph from rest sprint occupies just 4.9s en route to a top speed that has to be artificially limited to 155mph. You get all of this to the accompaniment of a crisp, muscular soundtrack that's emphasised if you select the provided 'Sport' mode. Lowered M Sport suspension with adaptive damping firms up body roll. Plus M Performance-specific variable ratio steering sharpens corner turn-in, while beefier M Sport brakes enhance stopping power. The alternative M40i petrol variant also uses a 3.0-litre six cylinder engine, that one putting out 360hp, and replicates this car's performance figures exactly. Both variants require you to accept a fairly firm standard of ride, but you can ease things by playing with the settings of the standard M Adaptive Suspension. The steering isn't quite as sharp and feelsome as we'd hoped it might be and there's a bit more body roll than you might hope for through the turns, but the M Sport Differential means that cornering traction is impressive. Overall though, this is a very complete package.
In keeping with its segment rivals, the exterior looks here are uber-subtle. To the point where many would mistake this car for an ordinary X3 with M Sport trim. Informed loyalist of Munich marque will of course know different, noticing the larger exhausts and the bespoke badging on the tailgate. Other smart touches include bespoke 20-inch M light alloy Double spoke M wheels finished in bicolour Orbit Grey. And a Cerium Grey with black finish for the kidney grille, plus bespoke calipers for the M Sport braking system and Cerium Grey mirror caps. Inside, apart from a smattering of extra M badges and anthracite headlining, the emphasis on subtlety continues, though you can lift the cabin with options like red leather upholstery. The twin-screened 'BMW Live Cockpit Professional' set-up is now standard. That brings a 12.3-inch instrument binnacle display and a 12.3 'Control Display' for the centre of the dash. Plus you get the 'BMW Intelligent Personal Assistant', a voice control system responding to the command 'Hey BMW'. 'Apple CarPlay'/'Android Auto' smartphone-mirroring is now (at last) standard. And the infotainment set-up now updates itself with 'over-the-air' upgrades, so you'll get into your X3 one morning and find it able to do something it couldn't do the day before. There's plenty of headroom in the back and comfortable space for a couple of adults. Plus you get a decently shaped by 550-litre boot which can be extended to 1,600-litres by folding the 40:20:40-split rear bench.
You won't expect an X3 M40d to be inexpensive and it isn't. At the time of this test in Autumn 2023, BMW wanted just under £64,000 for this car - about £500 less than is required for the M40i petrol version. That's about £4,000 more than Audi wants for its similarly powerful SQ5 TDI. Still, at least standard equipment is generous, with bespoke 21-inch M light alloy Double spoke M wheels, through the spokes of which you glimpse the bespoke calipers of the M Sport braking system. Adaptive damping is standard, as are BMW Icon Adaptive LED headlights with a High Beam assistant. You get electric front seat adjustment with memory buttons, variable sports steering and a man-made Sensatec leather-stitched finished for the dashboard. That's in addition to the features that you'd get with normal M Sport trim that include the BMW Live Cockpit Professional infotainment package that gives you 12.3-inch screens for the centre stack and there instruments. Plus there's M Adaptive suspension, Adaprive LED headlights, a Parking Assistant package, roof rails, sports seats, a HiFi loudspeaker audio system and LED front fog lights. If you've extra to spend, optional perforated leather climate seats would be nice, perhaps fitted out with active seat ventilation. Another option is a generously sized panoramic glass roof, while optional acoustic front side windows will complement the standard acoustic windscreen glazing to help create even lower noise levels in the cabin. 'Comfort', 'Visibility', 'Technology' and 'Technology Plus' packs are available at extra cost which group together the most commonly-ordered extra items.
Let's get to the WLTP efficiency figures. Those of the M40d are quoted on the combined cycle at between 38.7 and 42.8mpg, with CO2 emissions quoted between 171 and 190g/km. You might want to compare those with the stats of the petrol M40i, which are quoted on the combined cycle at between 29.7 and 32.1mpg, with CO2 emissions quoted between 221 and 204g/km. This diesel M-variant then, will be far cheaper than its M40i petrol stablemate to run. And, thanks to its lately-acquired 48V mild hybrid tech, far cheaper than its Audi SQ5 TDI arch-rival too - that car can only manage bests of 34.9mpg and 212g/km. What else? Well insurance is group 40E. And as usual with a BMW, there's a condition-based service indicator on the dash to advise you when your car needs a garage visit. You can check all of this using menus in the 'iDrive' centre-dash display and the car will give you four weeks' notice of when a check-up is needed so you have plenty of time to book it. Less familiar to some buyers will be the clever 'TeleServices' feature that comes as part of the BMW 'ConnectedDrive' services you can access through the iDrive infotainment system. Via this, before each service appointment is due, your X3 can automatically put in a 'TeleServices' call to your nominated BMW service centre, complete with detailed information on vehicle condition. You'll then get a call to arrange a service appointment, something you'll already have budgeted for if, at the point of original purchase, you opted for one of the two fixed cost 'Service Inclusive' or 'Service Inclusive Plus' packages which cover you for five years or 50,000 miles.
The reality of course is that an identically-engined BMW 3 Series Touring would be better to drive - and arguably more spacious for luggage-carrying too. But if you must have a mid-sized SUV with prodigious performance and acceptable running costs, it's hard to look beyond this one. A car this big and tall as always going to slightly struggle in transmitting 340hp to the tarmac, but this Munich model makes a decent fist of it. If all you want is performance from a Crossover of this kind, the alternative M40i green pump-fuelled variant might be a better choice. This M40d though, feels a more complete real-world product. Even if it's not a proper M car, it's certainly a proper performance SUV.