What Is Engine Braking (aka Downshifting) And Can It Hurt My Car?

October 3, 2017

Even if you've never technically heard of the term 'engine braking' or 'downshifting,' you've probably physically heard a large truck doing it, particularly if you've driven on steep mountain roads. 

Engine braking, or downshifting, is when a driver uses the engine to slow the vehicle down instead of applying the mechanical brakes. Although drivers in passenger vehicles, like you and I, can engine brake by shifting their transmission into a lower gear, it is most commonly used in large heavy vehicles, such as 18-wheelers and buses.

hill engine braking downshift
Image courtesy of PIXNIO

Modern semi trucks come equipped with a Jake Brake (nicknamed after the brake's manufacturer, Jacob's Vehicle Systems), a diesel engine retarder that, with the push of a button, shuts off fuel to a certain number of cylinders, which in turn stop sending power to the wheels. This slows the vehicle down without the driver needing to apply the service brakes. It is most commonly used to reduce speed on steep downgrades.

Is shifting into a lower gear while driving (engine braking) bad for my car?

When asking this question, you will find experienced technicians on both sides of the aisle with very strong opinions on the matter. Some say it's completely okay to use the engine to slow the vehicle when declining a steep grade and others who say it is not.

The conversation commonly revolves around the question – it is better to wear your brakes or accept the excess wear that using a lower gear may put on the clutch/transmission? It also comes into play that increased friction can heat up surfaces, especially brakes, so riding your brakes for an hour downhill is just never a good idea.

In general, it's a common misconception that engine braking is severely bad for engines, causing excess wear on the drivetrain. This is mainly thanks to that awful sound the Jake Brake emits. This is mostly a myth. Engine braking actually has a lot of benefits. It allows drivers to have improved control while slowing down, reducing the danger of jack-knifing that comes along with using mechanical brakes. Engine braking also preserves the life of the brakes by preventing them from overheating on steep downgrades. It even tends to break up excessive carbon build-up inside the exhaust system.

So can engine braking, or downshifting, ever result in damage to my car?

All will agree the if done incorrectly, downshifting when descending a grade can place additional strain on the driveline. All will also agree that riding the brakes down a long grade can result in excessive "fade." This was a more common occurrence in older vehicles but can happen to a newer vehicle when the brakes are pushed to the limit.

If you do try downshifting you want to be as smooth as possible. Here are some basic guidelines.

Let off the throttle when cresting the top of a hill and downshift one gear. With an automatic, you may not feel anything different, as not all gears provide engine braking and you may need to downshift one more gear to feel the engine braking.

What don't you want to do? Let your speed build up and then downshift to a lower gear – this will result in unwanted stress being placed on the entire driveline.

Of course, if you find yourself descending a hill and your brakes are failing, then, by all means, downshift and use the engine to help slow the vehicle. For further information, you should consult your owners manual as the manufacturer may have specific recommendations for your vehicle.

About the Author

Kimberlea Buczeke is an automotive expert at RepairPal, the leading online source of auto repair resources and estimates. With many ASE Master certified mechanics on staff who have decades of experience, RepairPal knows all the fine points of car repair.

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