MOST of you probably know that the diesel engine was patented by Dr Rudolf Diesel in 1892, once the German boffin had figured out how to get the thing chugging away nicely.

Rudi's baby may have been noisy and rather smelly but it had something like a 40% thermal efficiency advantage over petrol rivals, a point not lost on cost-driven shipowners, railroad companies, heavy goods hauliers and farmers.

The giant strides the heavy stuff has made in just the last decade should make you wonder where diesel would be today had fuel prices and global warming been burning issues in the 1920s and 30s.

Now, every manufacturer worth its fleet salt has to have a diesel in its bag, and not just one with a turbo. What they all want is what PSA pioneered - a high pressure common rail diesel (or a VW pumpe duse will do just as well). These units take Dr Diesel's lifework a couple of stages further and because a smallish manufacturer like Volvo hasn't got a common railer of its own (or Ford's) yet, it has to make do with a pair sourced from Renault.

Installed in the V40 estate and S40 saloon, these French 1.9-litre diesel engines give Volvo buyers the choice of 102bhp with 158lb-ft of torque or 115bhp with 188lb-ft. We tested the latter in a revitalised Phase II V40, fitted out in SE leather and red plastic wood.