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For reference, I've reviewed these three questions:

Manually shifting an automatic transmission?
Does Downshifting (Engine Braking) Cause Extra Wear and Tear?
Is engine braking harmful?

I drive a (new to me) 2011 Nissan Sentra. The transmission is automatic, and as with most newer cars, it has overdrive.

I'm always wary of wearing my brakes (and particularly the correlation between braking and gas mileage), so I try to avoid hitting them when it's possible. If I see somewhere that I'll need to slow down, I try to coast for long enough that I don't have to touch the brakes.

Failing that, I use engine braking to slow down whenever I can. Here's where I deviate from those questions. First of all, my engine is an automatic, so the answers relating to manual transmissions seem like they might be missing some critical parts. Also, I don't have any large hills I'm braking down, this is almost exclusively before / at a stoplight (so that I barely brake, just slow crawl, then accelerate when it changes).

My process is generally:
- 70-80 mph = coast to 60
- 50-60 mph = switch overdrive off, RPMs jump to ~3500, engine brake to 25
- 20-25 mph = shift from "D" (assuming 3rd gear here) to "L" (assuming 1st and 2nd)

This gets me down to about 10 mph, and I've never seen the RPMs go anywhere close to red line.

My question is largely about the overdrive scenario, and the long term maintenance repercussions.

First of all, my basic understanding of overdrive is that it's a higher gear (or possibly a set of gears with incremental gear ratios?) that the transmission shifts into when the car is going a good pace (40-45+). With this assumption, I feel that switching it off to engine brake will not damage the transmission, as it's merely downshifting, which is exactly what engine braking is about. Is this correct?

Additionally, is my understanding of engine braking sound as far as the basic gear shifting is concerned (disregarding the overdrive scenario)? My belief is that any wear would be on the opposite side of the contact locations in the transmission (since the wheels are pushing the engine, not the other - usual - way), so any additional "wear" would be unimportant to the overall life of the transmission.

Finally, and I believe this is very important to this discussion: by all accounts (manual, dealership, online), my 2011 Nissan Sentra has a Continuously Variable Transmission. I don't understand transmissions well enough to comprehend the subtle differences, but I do know the CVT has the option of infinite gear ratios, which means it can't possibly be a traditional "gear" transmission. I apologize for dropping this here at the end, but I don't know enough about CVTs to let that guide my questioning.

Am I damaging my transmission by using engine braking heavily in day to day driving?

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  • Not part of the answer below but relevant to "My belief is that...": one of the things that I find most comforting about cars (and most of the physical world, really) is that it doesn't matter what I believe. The car just is. Wear happens. I can find out why. I can fix it.
    – Bob Cross ♦
    Commented Sep 21, 2012 at 12:08

4 Answers 4

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My process is generally: - 70-80 mph = coast to 60 - 50-60 mph = switch overdrive off, RPMs jump to ~3500, engine brake to 25 - 20-25 mph = shift from "D" (assuming 3rd gear here) to "L" (assuming 1st and 2nd)

This gets me down to about 10 mph, and I've never seen the RPMs go anywhere close to red line.

If this is your procedure, you're well within the engineering tolerances of the design. Your car is not dealing with any kind of excess load. All is well.

With this assumption, I feel that switching it off to engine brake will not damage the transmission, as it's merely downshifting, which is exactly what engine braking is about. Is this correct?

Yes, you are correct. This problem clearly illustrates the situation: the overdrive button just allows the transmission to select an even higher gear, primarily for increased mileage at high speeds.

Finally, and I believe this is very important to this discussion: by all accounts (manual, dealership, online), my 2011 Nissan Sentra has a Continuously Variable Transmission. I don't understand transmissions well enough to comprehend the subtle differences, but I do know the CVT has the option of infinite gear ratios, which means it can't possibly be a traditional "gear" transmission.

Yes, this does make quite a difference in terms of the design but it doesn't change any of the fundamental answers.

Using the pictures from the Nissan CVT overview site:

enter image description here

You can see that there are two variable diameter pulleys connected by a very robust belt. As you say, this theoretically allows for an infinite number of gear ratios. Practically, there are plenty of engineering and human interface limitations that reduce infinity to a more manageable set of presets. There is a finite resolution of the pulley adjustment mechanism that allows the engine computer to direct the transmission. This means that, while not quite infinite, you probably have many many more effective gears settings than the five choices I have in my car.

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  • I don't know if this is still relevent with modern computer controlled transmissions. Many,many years ago my transmission rebuilder told me every manual downshift results in one less automatic upshift.
    – mikes
    Commented Sep 26, 2012 at 21:32
  • @mikes, I'm trying to understand: do you mean there are a finite amount of shifts for the whole transmission over the life of the car?
    – Bob Cross ♦
    Commented Sep 27, 2012 at 0:40
  • I think what he was trying to imply was, in his opinion it was not a good idea manually downshift an automatic transmission.
    – mikes
    Commented Sep 27, 2012 at 0:59
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    @mikes, in the absence of specific information about a particular situation, I'd have to say that he's wrong: moving the gear selector isn't going to automatically shorten the life of the transmission.
    – Bob Cross ♦
    Commented Sep 27, 2012 at 11:40
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Perhaps not really an answer, but I always wonder why people would rather put additional wear on an expensive, difficult to repair/replace, non-consumable item (driveline components) rather than on easy to replace consumable items (brake parts).

My "answer" is thus to reconsider your entire strategy and prefer your brakes over engine braking whenever possible, lest the amount of money you save on brakes makes an appearance (with compounded interest) somewhere else.

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  • 2
    Well, this is the entire thrust of trying to find out more information. In essence, is making heavy use of engine braking actually removing usable time from the transmission, or is it just balancing where wear happens? That's an actual question. How does heavy engine braking wear the transmission in comparison to rare engine braking and heavy (wheel) brake use?
    – rockerest
    Commented Oct 2, 2012 at 20:12
  • I was writing exactly this as a comment. I was exactly same guy, but changed my mind lately. Brakes are less expensive and can be changed DIY - not engine, not transmission. Of course use engine brakes on long downhill.
    – A.D.
    Commented Aug 3, 2017 at 18:07
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This may not apply to your CVT, but for others searching on this subject: I think the general answer for conventional automatics is yes, engine breaking does increase wear on your transmission. The situations you mention are probably light enough to fall within normal use, but my downshifting on a short off-ramp to slow from 70 to 30 (a habit I'm trying to break) is probably not. I don't worry much about dropping out of OD for an upcoming turn or a long hill.

An automatic transmission has about half a dozen gear assemblies that all spin around each other. The different gear ratios come from using clutch packs to stop different combinations of assemblies from turning. Under heavy engine breaking, all the energy that would be burned off in the break pads is instead burned off in these clutch packs as some assemblies are stopped and others allowed to turn, and in the transmission fluid. Dropping and disassembling the transmission to get at these parts when they start to slip is orders of magnitude more costly in both time and money than a break job.

I think knowing how to engine break is a useful skill. In an emergency on the freeway, slamming into 2nd while also applying breaks can help slow the vehicle more quickly. I'd rather spend some transmission life to avoid an accident than to just slow down for a stoplight.

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  • Your comparison isn't quite accurate - when you downshift to engine brake, the wear on the clutch packs is the same as any other shift, give or take, and the engine itself provides the resistance to slow the vehicle. This is different from brakes, where all of the stopping power is applied as friction to the pads. While shifting gears wears the clutch packs, and therefore every shift adds wear, it's not nearly as much as is applied to brake pads during a stop. If you maintain your transmission and change the fluid and filter at regular intervals, it's unlikely to fail all that much sooner.
    – cscracker
    Commented Oct 7, 2019 at 22:10
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I have never owned or worked on a CVT vehicle so this is nothing more than educated speculation on my part.

That said I know that CVT's are far more likely to fail from normal driving than a traditional automatic transmission. There is no way I could in good conscience advise someone to put any extra wear and tear on one. What your doing is operating out of spec. You are asking your components to do things they were never tested nor designed to do. While it is true that rebuilding a CVT is significantly cheaper than rebuilding an automatic transmission. However it's not cheaper (by orders of magnitude) than having your brake pads replaced and your rotors turned.

Really the only time you should engine brake a non manual transmission is if your vehicle came with the "tow package" from the factory. This means that your vehicle was intended to pull heavy loads and thus has enhancements to do so without impacting reliability. On any other vehicle (outside of a manual or an electric with regenerative braking) you are introducing forces to mechanical parts that they were never designed to experience. That is always bad.

Typically a vehicle with a tow package will have some or all of the following:

  • Larger diameter brake rotors.
  • Larger brake pads and calibers with extra pistons.
  • Reinforcement to the frame and subframe.
  • Possibly lower gearing but definitely beefed up internals.
  • A more stout differential possibly with a different gear ratio than non tow vehicles.
  • Larger radiator with larger and/or more powerful fans.
  • Higher amperage alternator
  • Plus more.

I just did a cursory search and every vehicle with a CVT I could find specifically says not to tow with it.

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