I was driving around in a rented diesel Renault Megane last week. Quite nice - apart from that awful looking back-end - and it drove well on the mountain roads in the north of Mallorca.

As expected, there was plenty of torque for going uphill, but unexpectedly, there was plenty of engine braking available for the downhill stretches.

Now this puzzles me. Large diesel vehicles have precious little engine braking - because they don't throttle the air going into the engine - hence the need for exhaust retarders, transmission retarders, jake brakes, and the like.

So, how do diesel cars provide engine braking?

I don't know the answer, but members might like to read this article which explains why there is a problem, and also explains the various options mentioned above by Mike.

I always felt a diesel engine braking was better than petrol because of the high compression ratio of the engine and the need for extra oomph to turn over the crank.

I always noticed how much more you needed to use the accelerator pedal in a diesel compared to a petrol engine.

Andy

I think also in large diesel engines engine braking is reduced because of the large heavy flywheels used in them.

Also becoming a problem in passenger cars as the heavier flywheels are being used to aid refinement/smoothness etc.

possibly:confused:

Diesel braking is a great thing.

The opposite is true for traffic jam plodding along because you can give the right foot a nice rest and just use the clutch with 1st & 2nd gears and no throttle. Will it stall - I've only managed it once, by accident. (parked, handbrake, release clutch, BUMP, oh 5hit!)

The new breed of electronic diesel /injector control are a lot easier to stall than the old world diesels. I cant remember the number of times I have so far stall the Superb, loads more than the Octy, and also the Transporter. I guess its down to much less torque at really low speeds from the pd units.

Andy