In Britain we call it "engine braking", I think Americans say the same.

A quick search says it heats the engine less than accelerating, so shouldn't cause overheating.

I don't see how that could overheat the engine. You're backdriving the engine from the wheels and fuel injection should be complete shit down so there is no combustion.

Engine braking doesn’t work on diesels, that’s why they have “Jake brakes”, that loud braaaaaaaaap you hear when they go downhill (and why you see signs at the edge of town saying “compression brake use illegal”). I highly doubt a diesel engine would overheat going downhill. (Not a diesel mechanic, but FWIW used to be an auto mechanic decades ago.)

https://en.wikipedia.org/wiki/Compression_release_engine_bra...

> Engine braking doesn’t work on diesels

Are you sure? I'm pretty sure I can engine break with my diesel car and do that pretty often in fact. Or I misunderstand what engine breaking is.

Am I sure? No, but I have been told this numerous times by actual diesel mechanics, and otherwise why was it necessary for Jacobs to invent the compression brake?

Your car also has rolling resistance and aerodynamic drag to contend with. Might work well at slowing a passenger car, not so much with a 50K lb. vehicle, hence the Jake brake.

> Your car also has rolling resistance and aerodynamic drag to contend with

I like to believe I'd recognize the difference, especially since it's a manual car and I can tell the difference between letting it roll in neutral and shifting down a gear which slows down the car :) Maybe it's not that it doesn't work on diesel cars but the effect is just less than with petrol?

In a gasoline engine, engine speed is controlled by a throttle valve which meters the air entering the engine. A carburetor or fuel injection system then provides an appropriate amount of fuel for the incoming air. If you release the accelerator the throttle valve shuts and the engine effectively becomes a vacuum pump sucking air through small openings that only flow enough air to idle, which causes it to actively slow down.

A diesel engine does not have a throttle valve. Engine speed is controlled purely by the amount of fuel being injected. This is why diesel engines can "run away" if an uncontrolled fuel source such as oil leaking from a turbocharger enters the intake, and why older pre-computerization diesels can be smoky under hard acceleration (or any time if poorly tuned). When you release the accelerator the engine stops receiving fuel and thus stops producing power, but aside from friction there's nothing working to slow it down. Air is sucked in more or less unrestricted and some energy is spent compressing it as the pistons rise in the cylinders, but much of that energy comes back out as the pistons come back down so the only energy loss in the system is what's converted to heat. You would get the same effect in a gasoline engine if you shut off the fuel pump but kept the throttle wide open.