Let me expand a bit on the engine braking of diesels. I have been paging through my old (20 years old!) notes and books from University days, but have not been able to find the particular reference, that’s why I hope some Mechanical Engineer reads this thread and can give us more definite answers. Google also turns up zilch.
First of all, of course diesel-engined vehicles do have engine-braking capabilities, but it is not something that is inherent in a diesel engine design. They sort of have to be forced to use themselves as brakes.
Here’s why (where are you mr Mech. Engineer?!):
(1) A diesel’s rev’s depend on the fuel distribution valve setting and the current revolutions of the engine (higher revs would deliver more fuel) Totally independent of how much air reaches the engine (which is what you need for the engine to 'pump’so that it brakes)
(2) Opening the valve by pressing the accelerator would deliver more fuel which would make the engine go faster. Fine.
(3) Lifting one’s foot off the accelerator would not really affect the business, because the engine’s current revs also determine how much fuel is allowed through the distribution pump.
(4) In fact, a diesel engine without the proper safegaurds, would, upon starting, accelerate indefinitely, opening up the valve more and more, purely because of the revs already reached until the point where the engine self-destructs or the fuel runs out or the fuel pump reaches its maximum delivery rate. This is sometimes known as overfueling - especially if one tinkers with the mechanism to deliberately cause a certain amount of overfueling. Diesel engine manufacturers usually expressly waive the warranty where overfueling is evident.
(5) This means that a diesel engine would normally be unable to provide engine braking - the rising revs would actually just deliver more fuel which would negate the lifting of the accelerator.
(6) Manufacturers therefore build in a mechanism to stop the diesel supply completely or almost completely when one lifts one’s foot off the accelerator. THEN the engine can actually act like a very high compression piston pump, and provide very good engine braking.
Petrol engines depend on the throttle butterfly valve, which controls the airflow, and the airflow controls the amount of petrol mixed in the air-fuel mixture. Therefore, “throttling” the engine would limit the airflow, which limits the fuel, which limits the revs, which provides engine-braking. Easy.
Now, I’m waiting for that Ph D (Eng) (Mech) to tell me I’m talking complete hogwash, but that’s what I remember. BTW, I’ve been talking mechanical/carburettor here, not electronic fuel injection, which might use different techniques. The underlying principle is the same though.
<hijack of the hijack>
Did you know that diesels actually cool down while idling? Unlike petrol engines which heat up.
</hijack of the hijack>
Back to the OP: Engine braking if used moderately and in conjunction with your normal brakes would not harm your car in any detectable way over the lifespan of your car.