Does engine braking use fuel?

Question

I often control the speed of my car by changing down gears. Is more fuel used as the revs increase?

My car is a 1990s variable-valve timing kinda badboy.

Answer 1

No! No! No!

For the last time (LOL) - in a modern vehicle the engine enters an 'over-run' state. That is, the car is moving the engine & NOT the engine moving the car. NO fuel is used. Anybody with a fuel computer that gives an instant display can see that fuel use drops to nil, and I mean NIL.

BUT, as soon as the forward speed & engine/gear is matched it will start to consume fuel.

This applies to both petrol injection & diesel engines.
In the petrol varient the spark plugs continue to fire to burn off any residual fuel to prevent cat damage, but no new fuel is added.

This is why it is MORE efficient to engine brake and keep the car in gear whilst going down hills than use the foot brake (risk of overheating on long decents) or coast in neutral (uses fuel to idle).

So you can keep on engine braking! It VASTLY improves deceleration if used with light brake application, sounds waaaay cool, uses no fuel and barely causes any clutch wear.
It is a very handy skill to have - much like left foot braking, double de-clutching and rev-matching (it's possible to change gear without the clutch...and no crunching!)

Answer 2

I would like to contribute answer in my point of view. I ride a motorcycle everyday to my campus. The road in my campus consists of hills. I extensively use engine braking alongside with the brakes on my bike rather than cruising in neutral. During the engine braking, I gradually shift down from 5th gear (my bike is a moped with 5 gear) all yhe way to 3rd gear at the suitable speed. I rarely shift down to 2nd gear unless I am cruising downhill at a very low speed. My bike use carburetor, but still I find that the fuel consumption has not increase, except if I ride my bike harshly.

In the nutshell, engine braking offers a good safety feature which assists a vehicle to reduce speed aside of using brake alone.

Answer 3

The amount of extra fuel it uses is next to nothing if any at all. During engine braking, the throttle is closed and the engine is under high vacuum. In other words, it is under very low load. Both a carb and EFI would cut back the fuel to the absolute minimum in this condition. However, it is true that engine braking does put a small amount of added wear onto the engine parts. Given that brakes are easy to change and piston rings are not, the advantages of engine braking is obviously not based on wear. Trucks use engine braking because they typically pull a large load; Slowing a large load causes their brakes to heat up very quickly which may compromise safety. Amongst other things, engine braking allows them to slow down and keeps their brakes cool and ready for that unexpected emergency stop.

Answer 4

No because the fuel flow is closed with your foot off the accelerator. Engine braking at one time was essential as the brakes were not very efficient and continuous use of brakes especially down hill resulted in Brake Fade which was very scary as they ceased to work at all because they were too hot.
This did put a strain on the Gear box and was the cause of premature wear.
Now with efficient non fade brakes it is not so necessary to use engine braking but sometimes on very steep hills the two can work together to put less strain a single components.

Answer 5

When you're engine braking, the revs increase but the flow of fuel doesn't. It's the lack of fuel that makes the engine continue to slow down. The engine is only given enough fuel automatically to idle, any more fuel supplied is via the accelerator.
Engine braking should only be used as gentle speed control when descending hills etc. Using the engine harshly to control speed causes engine wear for saving 0.0000005p worth of brake pads you could be causing 0.001p of engine wear!

Answer 6

It depends.

Some engine management systems cut fuel completely in such situations. Early electronically-injected petrol cars without catalytic convertors and some modern diesels can do this.
However, petrol cars with a closed-loop emissions control system are designed to control emissions by burning all the oxygen in the air passing through the engine, so may require fuel to carry out this task.

Answer 7

It uses a bit of fuel, unless you are on injectors. On carb units he vacuum increases although the throttle plate is almost closed. The increased vacuum pulls more fuel into the carb. On injection systems, it should make no difference. Saves a lot of brakes though.

Answer 8

no, the revs increase because the wheels are drivng the engine. the throttle is not opened - so you are just using the normal 'tick-over' amount of fuel.

Answer 9

Using gears to slow down s not a good thing,because it puts undue ware on the cogs in the gear box,in the end you may
find your self with a damaged box that will be very expensive
to fix.
So used your brakes to slow down also this lets other road users know you are slowing down by your brake lights.

Answer 10

Yes more fuel is used