Hello everyone and welcome! In this video
we are answering the question "Is it a bad idea to engine break in a manual transmission vehicle?"
And this is a discussion i've seen pop up in the comments,
I think there's some misconceptions about so I wanted to chat about it
but so what do I mean when I say engine braking all engine braking is, is when you're not on the throttle you let your
foot off the throttle and you're in gear
that's all it is and so it starts to slow the car down because you're in gear
there are some people who have said you know that they may use the clutch to slow themselves down by putting in the
lower gear and slipping the clutch or by using that shock from down shifting to slow yourself down
that of course is a bad idea to do you're just going to disrupt the balance of the car
and you're going to have clutch wear, but just simply letting off the gas
and letting the engine
slow the car down is absolutely fine. Now what's happening when you're doing this? Well basically in a gasoline engine what's happening is,
you let your foot off the throttle and so that throttle valve closes,
and now you have a vacuum between that throttle valve and your engine your engines trying to pull in air
but the throttle is closed so it's hard for it to pull in that air, and that's what's slowing you down.
A lot of people say it's the compression that's going to be slowing you down in these gasoline engines
and that's not the case because as that piston compresses up it does pressurize that air
yes, and it does take work to do that
but that work immediately goes right back into pressing that piston down very little of it is actually lost to heat in that transaction,
because you know engines are smooth running machines.
they're not supposed to lose heat in that scenario. So a lot of the energy from compression
just goes right back into pushing the piston back down
the real engine braking in gasoline engines comes from that throttle valve being closed and trying to pull that vacuum.
So you know is it a bad idea to engine brake?
No, you know there's actually benefits of doing this.
So essentially what you're doing is instead of using the brakes to turn the kinetic energy of the car which is
moving into heat you're using the engine to turn that kinetic energy into heat, so
putting heat into the engine and the engine has a
dedicated cooling system to cool it off so you can put a lot of heat into it, and it doesn't mind
it's able to reject that heat because you have the radiator and you have that cooling system that circuit
it's able to extract that heat out of it.
So is it a bad idea to engine brake?
No, and there's actually you know three major benefits to doing it and really applicable to both manual and automatic transmission vehicles
but here specifically talking about manual. You're going to have you know it's efficient and so if you love your foot off the gas
what happens is if you're in gear most modern cars will shut off fuel injection
so you're not injecting any fuel you're not using any fuel and it's an efficient way to run
because you're obviously not using any gas and so it's efficient
you're going to have less brake wear because you're using your engine to slow you down
so you're not going to be replacing your brake pads and rotors as often because your engine is slowing you not your brakes and
finally, you know if you're on
long steep descents
what happens is you use your engine to slow you down rather than your brakes so you don't overheat those brakes and start to
run into brake fade so on long descents if you keep using your brakes
eventually there's going to be too much energy into them
and they won't be able to reject any more heat and you're going to have brake fade
that's why you see those runaway truck ramps. You want to make sure you're using the engine to slow you down rather than the brakes on long descents.
Now is it possible to put too much heat into your engine from engine braking?
It's really not and I'll give an example
I used to have an Acura Integra and at one point my thermostat broke in my Acura Integra
and so the cooling circuit was always open thankfully it broke open and not closed otherwise
I would have ran into trouble
but because the thermostat was open there was always coolant circulating through the radiator and into the engine
now what this means is in scenarios where you
traditionally would want the radiator to be closed off, your engine is going to cool down. And so in
scenarios in my integra when I would go down a long descent if I climbed up let's say
i'm driving through the rockies if I was driving up and I started coming down these mountainous roads
and you know you've got six or seven miles of just straight downhill
what I would notice is because
my thermostat was held open and the cooling circuit was always running my engine coolant temperature would actually drop quite
dramatically when I was going downhill. And that's putting all of the heat from decelerating from engine braking into that engine
but it's also because you know you're not using fuel and so in scenarios where you're not using fuel
it really is a very little amount of heat that's going into that engine and so as a result because it couldn't close that thermostat
the engine cooled off
when going downhill so you know it's not something to worry about from a heat standpoint,
and you know modern cars of course will have a thermostat, so when you are going downhill they're not going to cool off
they're not going to get outside of an ideal temperature range that thermostat is going to make sure that the coolant around the engine
remains warm so it's within an efficient range.
So thank you guys for watching and if you have any questions, or comments feel free to leave them below!