Why prohibit engine braking?

  • When I learned driving in The Netherlands (in a car with a manual gearbox), I learned that on a down slope¹, I should switch to low gear and use the engine to brake, thus reducing the wear on the brakes. In Dutch, this is called op de motor remmen, which literally translates as braking on the engine.

    In the USA, I have seen signs prohibiting engine braking:

    no engine braking
    "No engine braking" sign outside Portage, Wisconsin. Source: Wikimedia Commons.

    What exactly is prohibited here, and why?

    ¹In The Netherlands — strictly theoretical ;-)

    Comments are not for extended discussion; this conversation has been moved to chat.

    there may be more great answers on https://mechanics.stackexchange.com/

    Annedoctal evidence: Living in a country without hydramatic gearbox cars there are signs "engine breaking required" in long and very inclined slopes. That's for safety reasons, if the breaks fails the engine breaking will reduce the acceleration. That's for passenger cars. Also the correct use of engine breaking is part of the drive license test.

    @jean: The word you want is "braking", not "breaking". "Braking" in automotive speak refers to slowing the vehicle down. "Breaking" something means damaging it, often by unexpectedly separating it into pieces. The two words are, unfortunately, pronounced the same.

    +1 for the Netherlands' reality footnote.

    I am so annoyed by 'using the the engine to break to prevent wear to the brakes'. Do you also not use your lights to prevent them to wear? They are MADE to wear, they are made to be a user-serviceable part. The rings on your pistons are not. It's going to be a lot more expensive to replace those. Not to mention the fact that you don't have brake lights when you brake on the engine...

    @CSharpFan On a downslope, braking may be more about preventing acceleration than about reducing speed.

    @gerrit ever been to the Netherlands? It's flatter than flat. Now I agree on your statement, but being from Belgium personally, I do think that it is thought the wrong way, it should indeed be used for ADDITIONAL control, not for braking when coming to a stop.

    @gerrit Carefully read the question and take a wild guess as to whether or not I have been to The Netherlands ;-). The question states explicitly that I learned this for downslopes, not for regular "I need to slow down" braking.

    @gerrit and others, you know better -let's keep the comments to the linked chat room above please :)

    "What is being prohibited here?" is a travel question, in the sense that it's always good to know how to stay out of trouble when travelling. But "Why?" (which is the title, and what shows up in HNQ) seems completely off-topic, and perhaps best suited for politics.stackexchange.com.

  • Completely different thing! They are referring to the "Jake Brake" in heavy trucks, where the trucker opens a portal to the depths of Hades and you hear a very loud


    sound, wrap the pillow over your ears, and call the Realtor in the morning.

    This does not apply to regular old downshifting in a gasoline car, where you spin the engine to use your cooling system as a dynamic brake. If trucks would just do that, nobody would complain.

    The Jake Brake (or more properly the Jacobs brake) makes engine braking more efficient. Normally a diesel gulps a full load of air (no throttle plates) and no fuel is injected when it is in engine braking. The engine consumes energy in the compression cycle but regains that energy in the expansion (normally power) cycle. The Jake Brake prevents that regain, by opening the exhaust valve at the start of the power cycle instead of the end. This instantly, and percussively, dumps a shot of 200-400 psi air directly out the exhaust stack.

    Comments are not for extended discussion; this conversation has been moved to chat.

    This, exactly. A Jake brake turns that massive, diesel engine into a 2-stroke air compressor, drawing in through the intake and pumping out through the exhaust. This is why the pitch is twice as high as the engine, running normally. My dad was an OTR driver for decades. His later trucks had a 2-stage Jake, where half of the cylinders switch on the first stage, then all of them on the second stage. First stage wasn't as noisy. Second one ... ooh yeah.

    I worked extra as a garbage man 20 years ago and drove a Volvo FL (maybe) that was a couple of years old. It was a "city" model with automatic gearbox and I'm pretty sure it also had an automatic exhaust brake system or maybe even a compression brake that was applied as soon you nudged the brake. It let out a rather nice muffled 6-cylinder growl while gently rolling to a halt. Saved quite a lot on the brakes. Is this not available on the US market still?

    Here is a video of a truck using them: https://www.youtube.com/watch?v=qocMoTOVn6Q

    @DanNeely I stand corrected. I believed exhaust braking was what made that noise, but it appears it's a different thing to compression release braking.

    As this is now protected I must comment to point out that in many places, on steep hills there are signs telling you you **MUST use engine braking** to avoid overheating your brakes. This is a real problem on long descents, riding the brakes causes them to overheat and stop working, whereas your engine can slow the vehicle for as long as you like.

    They mean you must use engine braking generally, of which the Jake Brake is only one kind. A truck with that brake can engine-brake without it perfectly well, by going a bit slower, downshifting more, spinning the engine faster, and using those spinning losses as the brake. So requiring engine brake and banning the Jake Brake are compatible.

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Content dated before 7/24/2021 11:53 AM

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