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?