3 ms·

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 brak

• diggan 1y ago
  > 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?
  • mikestew 1y ago
    Manual tranny, why didn't you say so? :-) Yeah, I guess you would notice the difference. But I think you've hit on the difference, as I vastly simplified what is going on. Not that I expected you to read the link I gave, but it does give some explanation as to what's going on. And what's going is that the pistons are still going up and down because air is continually drawn into the engine. Air is compressed, and even though there is no fuel to make it go bang, that air still needs to uncompress and so returns a lot of the energy back to the crankshaft. Ergo, very little engine braking. As a personal example, our diesel Sprinter van (automatic tranny, FWIW) had some degree of engine braking, but so little that I wouldn't rely on it for much more than coasting to a stoplight or other low-stakes slowing. If I'd like to stop sometime in the next day or two, I hit the brake pedal.
    • diggan 1y ago
      [dead]