A reader asks:
We have a 2004 Honda Pilot with automatic transmission which we drive regularly in the mountains. My husband uses the transmission completely in lieu of the brake pedal (except when approaching a stoplight or sign), and I have NEVER seen anyone drive this way. Switching from gear to gear in very short distances in lieu of using a brake pedal – I am talking up and down and up and down in the span of 100 yards or so. Will he burn out the transmission? Burn up the oil?
The concept of “engine braking” is a good one. If you’re trying to slow down your vehicle, and you have plenty of space and time to work with (ie, the stoplight is half a mile away), downshifting is a smart way to slow down because:
- It reduces fuel consumption, as the engine doesn’t burn more fuel when you downshift (it only burns fuel when you push the accelerator). When you downshift to slow down, the engine basically stops burning fuel completely. This is preferable to coasting out of gear (or shifting into neutral) as an idling engine always burns fuel.
- Downshifting reduces brake wear, as well as keeping brakes from overheating.
However, you can absolutely go too far. As a general rule, engine braking should be used to reduce the need for using your brakes, but never replace them.
Engine Braking Can Be Very Smart
Reducing fuel use is the main reason most people engine brake, but there are situations (like towing or mountain driving) where engine braking is important because it reduces brake use. When towing or driving in the mountains, brake pads can get hot very quickly. They will begin to fade, reducing effectiveness the hotter they get. At some point, they can even fail.
So, if you use engine braking to prevent brake fade and/or brake failure, that’s a pretty smart idea. Most truck drivers are taught to make extensive use of engine braking in their day-to-day driving, as it’s a smart way to save fuel and prevent brake failure on their trucks (particularly during mountain driving).
However, engine braking is not a substitute for regular braking. If you need to stop or slow down quickly, it doesn’t make sense to try to do this with the engine. Not even the most grizzled truck driver would try to bring their rig to a quick stop by downshifting.
Engine Braking Concerns
Engine braking isn’t necessarily bad for your engine or transmission, but it can be if you do it incorrectly. You have to balance the benefits of engine braking against some other factors:
- Shifting frequently increases clutch wear on a manual transmission, and can lead to high temperatures* in an automatic transmission
- If the engine braking is really aggressive, it can lead to very high engine RPMs that can lead to increased piston ring wear over time
- If downshifting is keeping you from using the brakes when you really should, it could potentially cause an accident
Based on our reader’s description, her husband is having a little too much fun downshifting, and should probably hit the brakes a bit more often.
What’s more, downshifting an automatic transmission while going downhill isn’t a best practice. Most transmissions respond poorly to this particular use, as they are not usually programmed for constant manual shifting. Unless they have that ‘select-a-shift’ mode or paddle shifters (or similar), manually controlling the gear selection is a formula for an overheated transmission. A Honda Pilot transmission can probably take the abuse (these transmissions where built for towing), but it wouldn’t be a surprise to learn the transmission was getting nice and hot as a result of this constant manual control.
To sum up: If your brakes are overheating, you’re probably not making enough use of engine braking. If you’re trying to use the engine for all your braking, you’ve gone too far the other way. And if your wife is wondering if you think you’re Mario Andretti? It’s probably time to back off.
*High temperatures will kill an automatic transmission in short order, so you really have to watch this. I frequently use my nose to determine when my transmission gets hot, as most vehicles don’t have a temperature gauge for the transmission. You have to smell for burning transmission fluid, and then pull over to the side of the road and let the engine idle so the transmission can cool. You do NOT want to turn off the engine when you’re pulled over, as that will stop the transmission fluid from flowing thru the cooler and shedding all the excess heat. Instead, just let it idle for a few minutes.