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Slowing car

When driving on a straight road, I downshift to help slow my car when I see a red light to save the brakes. I do this in a manner so it never goes more than 3000 rpm. My friend says this is bad for the engine; I say it’s okay because I don’t go over 3000 rpm. Who’s right?

It’s not “bad for the engine”, but it will wear out your clutch much quicker. A clutch replacement is $1500 or so while brakes cost a lot less.

If you have an automatic it will speed up the wear on the transmission shift mechanism.

I downshift on a long downhill grade in the mountains where overheating of the brakes is a real possibility.

For normal city driving it is a distracting practice with no real benefit.

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Unless, of course, you do it properly and double-clutch… But not many people know how to do that anymore.

Both of you are right. Using engine vacuum for braking can draw a minute more amount of oil into the combustion chamber. On a new vehicle, this is very very minimal and actually helps lubricate the rings and cylinder walls. But as the engine ages, it can increase oil consumption and too much extra oil on the cylinder walls at some point towards the end of service life, could be harmful.

Not exceeding 3000 RPM really mitigates the effects so unless the vehicle is a real oil burner, I’d do it. I do do it in fact.

Next question is automatic, manual, DCA, or CVT?

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Automatic. It’s a 2018 Camry with the “sport” transmission, 8 forward gears.

Do you have paddle shifters or a manual gate with up and down on the shifter? If you have either, you are OK to manually shift it.

Don’t you think it would be better to use the brakes as they were intended to do . It also turns on the brake lights so people behind you can be aware that you are slowing down and might have to stop sooner then you planned.

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both excellent points, @VOLVO_V70

Just use the brakes. That’s what they’re there for.

As long as it isn’t an extreme downshift, something that makes a lot of noise and jolts the vehicle, this won’t harm the engine or the transmission. And it does help keep the engine in its best rpm range for quick acceleration. That can increase your options if you need to use an evasive maneuver for a driving safety situation.

With an auto it’s still wearing the clutches. Especially forcing it to change against the compression of the overrunning engine. And auto clutches are even more expensive to replace than a manual trans clutch.

So does up shifting. Each time you drive away from a stop the transmission is going to up shift 6 or 7 times, perhaps 20 times a day. If a driver down shifts twice a day is this something to be concerned about?

Not sure how you get 2 a day. The original post said every time he encounters a red light. Yes, no kidding accelerating up through the gears wears the clutches, it’s just a fact of necessity in using the gearbox. The point is that forcing the trans to do the same going back down the gears will be twice the wear.
Whether that’s “a concern” is up to the owner/driver.
Auto trans clutches have a FAR easier time of it than manual trans clutches but every use is cumulative and the wear is dependent on the line pressure and the force being applied. In deceleration the line pressure may be lower (depending on the vehicle and how the ecu & throttle position influence the presure) meaning longer engagements time for the clutches - which equals smoother shifts but more wear.
Whatever the amount, it still adds to the wear. Potentially double.