"Responsible" Downshifting or asking for trouble?

[Pilot1226]

A few months ago, I got an idea in my head that I wanted to get myself a Forester 6MT. I learned how to drive on a stick years ago, but wanted to brush up on my skill, so I borrowed a friend's car and bombed around town in it to help get my skills up to snuff. And then, I realized that I live a few miles west of New York City, and traffic is absolute hell. While I could do it, I didn't really want to do it. Perhaps if it was a second car? Enter WRX/BRZ!

 

That being said, I got into the habit of using my paddleshifters on my Outback to downshift when I notice a light has changed, traffic is slow or stopping, exiting a freeway, etc.

 

I'm not using it to replace braking, but I am using it in conjunction with braking, and I'm obviously not having to depress the brake pedal as hard as a result.

 

Basically, I'll use my brakes if I'm above 2000 RPM, and I'll downshift once I'm at or below 2000 RPM, lightening up my foot on the brake pedal and essentially letting the drag of the engine slow the car down. Since I'm not using Manual Mode, the car generally puts itself back into "D" as soon as I'm below 10 mph or if I start accelerating, once it exceeds 2500-3000 rpm, just like a 4/5EAT would have.

 

The car doesn't seem to disagree with the downshift points, I'm not getting any type of engine jerk or oil burn that sometimes happens with engine braking, but I'm worried about the things I can't see.

 

I know there's essentially two schools of thought about this: either downshift and save your brakes, or don't downshift because a brake job is cheaper than a transmission job.

 

But, these "rules" are for true manuals, and the CVT is the farthest thing from it. What's your take? Am I possibly doing harm or accelerated wear to either the transmission or components (like the CVT Fluid), or is it so minimal that it's a non-issue?

 

I do plan on trading in the Outback soon, so I'm not terribly concerned about it as if anything should happen I have my extended warranty enhancement, but I don't want to start the new ride (which will be a Legacy 3.6) on the wrong foot.

[BradLegacy2017]

I don't believe that it is harming the vehicle at all to downshift as you have explained. Afterall, you are using the manual shift modes and downshifting as intended by the manufacturer.

[inthedeck]

^^ +2. I use mine, all the time, just wish I could install the transmission cooler, like the thread created by Opie some time back. Now, that would ease my mind a bit, but, no worries here..and I have 33K more miles to figure out if there will be a problem. I highly doubt it, though.

[upstater]

Forcing the CVT to engine brake regularly with the paddle shifters will add stress to/and reduce the life of the CVT

 

While CVT fluid is expensive, the real expense is the belt and tensioners, and the fact that right now Subaru seems to fix problems not by opening the transmission, but by replacing it with a new unit (from what I have seen so far, some tech here may correct me).

 

Using a manual transmission car the same way will also increase wear on the transmission, but a clutch is a replaceable item in a manual transmission, vs having to drop and service (or replace) the entire CVT transmission if it wears out prematurely. That said, clutch replacement cost is also multiples of brake pad service.

 

Brake pads are cheap, so downshifting like you describe isn't a good way to reduce your service costs, especially in a CVT.

 

If you want to surmise the best answer, as to, "what would a Subaru engineer say" you can look at how a Subaru with Eyesight and Adaptive Cruise controls increasing vehicle speed during a long hill descent.

 

It brakes, it does not downshift. I tested this last weekend while driving in the Berkshires. So maybe ask yourself, why doesn't Eyesight ACC downshift to slow vehicle speed?

 

The only time I "engine brake" with paddleshifters is on the occasional long descent (e.g., Route 7/9 from Brattleboro to Bennington VT), if you downshift while descending a grade it holds the lower gear (manual mode is not required for this) controlling vehicle speed, reducing the need to brake and keeping the brakes from heating up which could happen if I rode the brakes for the mile or two descents in some sections.

[Haboob]

Engine braking on a manual is absolutely okay, so I wouldn't see why it would be any different on an AT.

 

Haven't had any issues on either of my past manuals (130k and 90k on this one now). I'll most likely be doing it on the 3.6R assuming I can find one available.

[upstater]

if you plan to keep the car past the warranty, a CVT repair will cost many multiples of a brake job, assuming that they even start servicing CVT's vs just replacing them with a new unit (about $13,000), so have at it.

[Pilot1226]

Right. That’s the question... is it really increasing wear? What would get worn on the Subaru CVT? The chain itself?

[ehsnils]

Considering that the gearbox has software protecting it and the engine the risk is lower for the CVT than for a manual. The torque when engine braking is also lower than the torque when doing full acceleration so don't worry.

 

One point behind doing appropriate engine braking is to use it in long downhill conditions to avoid overheating the brakes. Overheated brakes are useless.

 

Also realize that the cruise control can utilize the engine braking automatically too.

[upstater]

Considering that the gearbox has software protecting it and the engine the risk is lower for the CVT than for a manual. The torque when engine braking is also lower than the torque when doing full acceleration so don't worry.

 

One point behind doing appropriate engine braking is to use it in long downhill conditions to avoid overheating the brakes. Overheated brakes are useless.

 

Also realize that the cruise control can utilize the engine braking automatically too.

 

Engine braking (via a downshift) is appropriate when driving down a long descending grade (Berkshires, Rockies, etc).

 

I do use the paddle shifters to hold a gear in those conditions, though for the 2-3 mile descents in the Berkshires I am pretty sure I won't overheat the brakes.

 

My car, with Eyesight/ACC, does not downshift to control vehicle speed (even on those long downhills, go test it yourself). While ACC is engaged and going downhill, it only brakes to maintain the set speed.

 

This thread now has become a "how can I legitimately claim that my obsessive need to paddleshift instead of braking won't be worse for my car than just using the brakes?"

 

The answer is, you can't, you will save some brake pad in exchange for some more wear on your CVT, but it is your car, so go for it.

 

PS: haven't you guys ever listened to Click and Clack? Some version of this story occurred multiple times on their show over the years...

[crudzinskas]

You should probably stop driving your car so that you don't wear out your CVT.

 

In all seriousness, as long as you aren't down shifting to redline then you should be just fine. The CVT is programmed not to shift in a way that would damage itself. When I use the paddles to down shift I normally end up right around 3000rpm which isn't much more than when accelerating at a moderate level.

 

Subaru recommends in the manual to utilize the paddle shifters for downshifting as well. Using adaptive cruise also uses the transmission to regulate speed more often than it uses the brakes in my experience. It is very nice in that respect because ACC can use the CVT to downshift in much smaller increments than you can with the paddle shifters which is why it is almost completely unnoticeable unless you are looking at your tachometer.

 

For those who are worried about the CVT being less robust - it very well could be, probably not but it could. That being said, if it is going to break at low mileage - say 80,000 miles because of a design flaw, it's going to break no matter how careful you are with it. If it is designed well, which for all accounts it seems to be, then as long as you aren't racing your car everyday it should last within the expected amount Subaru intended. If I had to guess, I'd say 150,000 miles is reasonable and probably why the CVT fluid is considered lifetime. Most people don't keep cars this long; although, I hope to drive mine until it's a rust bucket - hopefully 200k miles lol.

 

Despite what most people expect - most major parts (the ones you hope you don't have to replace ever - engine, CVT, etc..) and electrical components are designed to last 100,000 miles. Most last longer, but if they last about that long it's engineering well done by industry standards.

 

tldr; downshift as much as you'd like!

[upstater]

Using adaptive cruise also uses the transmission to regulate speed more often than it uses the brakes in my experience. It is very nice in that respect because ACC can use the CVT to downshift in much smaller increments than you can with the paddle shifters which is why it is almost completely unnoticeable unless you are looking at your tachometer.

 

Using ACC, the car uses the brakes to slow it down, not the transmission. It will downshift, like any automatic, as it slows down assuming you are slowing to a stop.

 

You might want to go find a long downhill, use your ACC, and see what actions the car takes to hold your set speed.

 

That is what I tested over the Berkshires on Friday (not because of this thread, I went to see my mom for Xmas).

 

It stayed in 6th gear, the entire descent ~55mph, and as it gained speed over the set point the car braked to keep it at the set speed.

 

This is a good place to mention that manually downshifting dropped it into 5th or 4th, and in this case the engine/transmission held that gear (shifter not in manual mode, I just paddle shifted) and kept my car from speeding up as much.

 

On a long descent, my car never downshifted as a way to keep the car from gaining speed, it just rode the brakes.

 

i.e., Eyesight ain't as smart as a human driver in long hill descents, and Eyesight is not programmed to change the transmission gear to slow the car down, it brakes.

[Pilot1226]

My biggest concern with the CVT would be the fluid itself. Subaru has made themselves a very robust, powerful CVT. Possibly the best - or very close to it - in the world. Their chain design is brilliant. Where other automakers were going one way (belts), they went another (with the chain) and it's paid off for them.

 

But, like any lubricant or fluid, heat is a problem. So, I think it would probably be better for the longevity of the fluid to avoid having it get hotter than it has to, since that really contributes to degradation.

 

The other issue is that the CVTF is not really "user serviceable." I know that you can absolutely DIY a fluid drain-and-fill, but man, it's a pain. I imagine this excess heat and degradation of the lubricant properties is why they suggest you change the CVTF if you're towing.

 

The only way to know "for sure" is to have some sent to Blackstone for analysis, but it'd be a very difficult test to do... having car "A" not use paddles at all, and having car "B" use paddles to downshift.

 

Obviously if the fluid degrades, and there's microscopic metal fragments floating around the CVT, eventually it'll find its way and gum up the valve body or a solenoid.

[crudzinskas]

It stayed in 6th gear, the entire descent ~55mph, and as it gained speed over the set point the car braked to keep it at the set speed.

 

On a long descent, my car never downshifted as a way to keep the car from gaining speed, it just rode the brakes.

 

i.e., Eyesight ain't as smart as a human driver in long hill descents, and Eyesight is not programmed to change the transmission gear to slow the car down, it brakes.

 

Thanks for giving your observations. Obviously this isn't an apples to apples comparison, but the majority of hills I go down it does in fact vary the RPM as much as it can before it uses the brakes. While going around 55mph @~1600rpm transitioning to a downhill, I've experienced the rpms going up to and hold as much as 2500 rpm before it brakes and sort of repeats that cycle.

 

Not to get too off topic but at the very least the car seems to "know" when it is on an incline. For example when I release the gas pedal on a level road (going about 35 mph or less) the engine rpm drops about as low as they can go, while driving on an uphill incline at the same speed and releasing the gas, the rpms will remain high as I coast until almost a complete stop, as it must expect to need that certain gear ratio to continue up the hill if you were to reapply the gas.

[Pilot1226]

It has an inclinometer... it uses the incline to determine whether to apply hill assist. So it makes sense to me that it would be useable in other situations.

[upstater]

Thanks for giving your observations. Obviously this isn't an apples to apples comparison, but the majority of hills I go down it does in fact vary the RPM as much as it can before it uses the brakes. While going around 55mph @~1600rpm transitioning to a downhill, I've experienced the rpms going up to and hold as much as 2500 rpm before it brakes and sort of repeats that cycle.

 

Not to get too off topic but at the very least the car seems to "know" when it is on an incline. For example when I release the gas pedal on a level road (going about 35 mph or less) the engine rpm drops about as low as they can go, while driving on an uphill incline at the same speed and releasing the gas, the rpms will remain high as I coast until almost a complete stop, as it must expect to need that certain gear ratio to continue up the hill if you were to reapply the gas.

 

It is a CVT, the RPM varies in any given gear depending upon your speed. Go find a long hill and test the ACC, a hill where the car (without shifting, accelerator or brake input) gains speed due to gravity, and see if it downshifts or brakes to control vehicle speed...

 

I already tested it, and the car does not downshift, it brakes, I am not sure your results will vary, unless your Eyesight ACC works differently than the system in my 2017 does.

[crudzinskas]

I believe what you're saying, but it does appear we have different experiences. I seem to experience both how you describe and how I describe ACC to work.

 

But to sum up on the original question, based on my engineering knowledge and experience I would say that downshifting doesn't harm your CVT or it's fluid in a significant way.

 

This is just a car forum, so take all advise with a grain of salt and pick whatever seems most logical to you.

[Brisvegas]

Engine braking (via a downshift) is appropriate when driving down a long descending grade (Berkshires, Rockies, etc).My car, with Eyesight/ACC, does not downshift to control vehicle speed (even on those long downhills, go test it yourself). While ACC is engaged and going downhill, it only brakes to maintain the set speed..

 

I find this discussion on driving down long descending grades interesting.

Page 35 in the "Owner's Manual supplement for Eyesight system" would seem to back your observations on ACC braking on steep descents.

 

" .. .. In the following conditions do not use adaptive cruise control ...

-Steep downhill grades. The set vehicle speed may be exceeded.

-On a steep continuous downhill grade. The brakes may overheat..."

[crudzinskas]

Good find! Definitely supports how both of our personal experiences can be true. Ohio's hills are not very steep to say the least which is probably why I don't experience ACC riding the brakes very often. The "adaptive" in ACC definitely lives up to its name.

[Pilot1226]

I believe what you're saying, but it does appear we have different experiences. I seem to experience both how you describe and how I describe ACC to work.

 

But to sum up on the original question, based on my engineering knowledge and experience I would say that downshifting doesn't harm your CVT or it's fluid in a significant way.

 

This is just a car forum, so take all advise with a grain of salt and pick whatever seems most logical to you.

 

The only way I could see how it would harm the CVT is if:

 

Downshifting caused the CVTF to become hotter, and,

The extra heat leads to abnormal accelerated deterioration of the CVTF, and,

The CVTF then cannot do its job to lubricate the CVT and surrounding components.

 

Unfortunately I can't see the CVT Temperature in my 2011. If this is an option on the newer Leg's and OB's, that would be very cool if someone could check the temps after a control drive (for example, normal driving, no downshifting), and then the same route with downshifting.

[upstater]

The only way I could see how it would harm the CVT is if:

 

Downshifting caused the CVTF to become hotter, and,

The extra heat leads to abnormal accelerated deterioration of the CVTF, and,

The CVTF then cannot do its job to lubricate the CVT and surrounding components.

 

Unfortunately I can't see the CVT Temperature in my 2011. If this is an option on the newer Leg's and OB's, that would be very cool if someone could check the temps after a control drive (for example, normal driving, no downshifting), and then the same route with downshifting.

 

Physics, friction goes somewhere, if not to the brake pads, than to other parts of the car, in this case transferred via the steel belt in the CVT (which will absorb some of that wear and tear if you switch to using the transmission more, in lieu of your brake pads, to constantly slow the car down).

 

It really doesn't matter to me if you downshift your car while driving around town because you want to pretend it is more like a manual transmission car (though, in my defense, that behavior in a manual transmission car is also going to increase your repair bills)

 

It probably will only cost you more money if you are trying to keep the car for 10 years or more and drive it into the ground.

 

PS: Click and Clack podcast is still available, common sense mechanical advice:

 

https://www.cartalk.com/content/when-should-you-downshift-manual-transmission

 

I know, I know, you are going to respond that a CVT transmission is different! I agree, it costs a lot more to repair and service a CVT vs a manual transmission with a clutch...

[Bolt]

I personally am trying to downshift less as I think it is bad for the engine. It says in the owner's manual that downshifting can be the cause of excessive engine oil consumption. Brakes are way easier to change than engine or transmission.

[miinike]

i have a question, when in the "D" mode? will the paddle shifters still engage when tapped? or does the Tranny have to be in the "M" mode in order for the shifters to shift gears? i have the 2015 version and I inadvertently tapped the down shift while in "D" mode and it shifted to a quick slow speed..

[Yoda_One]

Yes

 

Laughing at oneself and with others is good for the Soul![emoji2]

[miinike]

Yes

 

Laughing at oneself and with others is good for the Soul![emoji2]

 

Thank you. is there a specific speed where the gears will not shift for safety reasons? i was driving along at about 30mph and the gears downshifted when i inadvertently hit the down gear.

[Da Roo]

The CVT will not shift if it will harm the engine. You will be fine.

 

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