What is it?
Finally the Infiniti EX has got its first diesel engine, around a year after UK launch, a few months after its bigger FX sibling and the new M saloon, and not a moment too soon by any other reckoning.
There is undoubtedly an appeal to the free-revving, 300bhp 3.7-litre petrol unit, until now the only engine option available in Infiniti’s coupé crossover, but its frenetic, 7500rpm personality is matched by thirst at the pumps.
This new direct-injection V9X diesel engine is identical to the one in the FX30d and loosely related to the unit in the V6 Laguna, but with a new turbocharger, block, crankshaft, intake manifold and sump.
It also has a compacted graphite iron block, both lighter and stiffer than cast iron, which improves refinement and adds strength between the cylinder banks, where the stresses are highest. The single variable-nozzle turbo is mounted in the 65deg vee.
What’s it like?
On the road it’s an impressive, if slightly vocal piece of engineering. For starters, it's got a redline above 5000rpm and spins freely up to it. Peak torque of 406lb ft appears at 1750rpm, which means that you can lock it in fourth gear (roughly 20mph/1000rpm) and dispatch challenging B-roads or motorway sliproads with at least as much ease as in the petrol version.
In fact, the pairing between diesel engine and gearbox is much better resolved and less fidgety than in the manual, but still retains the typical Infiniti-style changes, where it holds the lower gears for engine braking if you lift off from high revs.
Infiniti claims 33.2mpg on the combined cycle for the new engine and 224g/km of CO2. We saw a displayed 28.9mpg on the test route, which shows an improvement in fuel consumption of around 20 per cent over our petrol-engined EX37 long-term test car, which achieved 23mpg on the same roads.
That’s less than the claimed 40-plus mpg in the similarly priced Mercedes E350CDi coupé or substantially more expensive BMW 635d, but the Infiniti’s four-wheel drive and ‘everything but the kitchen sink’ spec in the Premium edition - which now includes a lane warning system that alerts you and redirects the car if you drift into the adjacent lane on a motorway - will readdress the balance with less economy-conscious drivers.