mdreef

I have really enjoyed the paddle shifters on my 2010 E550 and I am trying really hard to avoid warping my rotors..so for that reason I have been downshifting more than I ever have with any other cars.

I live and drive in Houston where roads are flat so I typically downshift as I get to a red light or stop sign. Of course, I could drive a bit less aggressively, but that's really, really hard to do with an E550!

So my questions are:

1. Does downshifting too much cause strain on the transmission and engine?
2. Does downshifting decrease fuel efficiency?

Thanks for sharing your wisdom.

Electric Lizard

You downshift to accelerate and brake to decelerate. Since you live in Houston, you should join one of the local car clubs to attend some of their coached driving events. There a few excellent programs.

Live Oak

IMO, a few brake jobs are a lot cheaper than one transmission job.

In the mountains, downshifting is sometimes a good idea. In your area, a "mountain" is the nearest overpass.

CEB

1. Yes
2. Yes

BenzV12

For fuel efficiency , manually downshifting deteriorates fuel consumption . I recently had a trip of 647 kilometers visit / return
First : 323 kilometers only manually downshifting delivered 9.6 lt/100 km
Return:323 kilometers fully auto shifting 8.4 lt/100 km

I don't think in electronic wise, you can't damage your tranny from manually using but mechanical wise some parts might be in long run like turbo.If you turn on ECO and manually downshifting in lights , (you know you use higher RPMs rather than let off your gas pedal ) sudden stop without letting your RPM drop gradually could damage turbo blades because turbo blades need some rest in idle when you stop the engine because blades rotate or spool w/o getting oil

hyperion667

what about a manual?

Electric Lizard

Brake pads are much easier to replace than clutches. The mantra still holds: downshift to accelerate.

Arrie

1. I would not worry about this. With a manual transmission it is a way of normal driving to let engine "weight" to slow the car down with shifting to a smaller gear. Transmissions were built to be strong enough for this and I don't think they weakened them with automatic trannies that actually have the soft "propeller" component, the torque converter, with them. Any impact with automatic from down shifting is far less than with manual.

2. I don't see a problem here either. When the momentum of the car pushes the engine it takes very little, almost no gas.

Arrie

Could you explain your two "Yes" answers. Would like to learn here.

CEB

Sure.

The questions were as follows:

1. Does downshifting too much cause strain on the transmission and engine?
2. Does downshifting decrease fuel efficiency?

I'll address the second question first

A modern automatic transmission is designed for optimal efficiency. When you compare EPA mpg figures for cars that are available in both manual and automatic transmissions, you'll see that the autos always have the better numbers. Accordingly, trying to shift manually will decrease efficiency.

Now, for the first question.

Remembering that the transmission is designed to always be in the "best" gear, overriding that significantly will cause excess strain.

There are, of course, a few exceptions. Like others have said, using the shift paddles to "announce" your intention to accelerate is fine.

The other exception is to keep your brakes from overheating on very long, steep downhill grades. In that case, it is better to sacrifice a bit of transmission life than to arrive at the bottom of the hill with no brakes. This should be extremely rare.

Going down Pike's Peak is the one time that I downshifted to preserve braking. Halfway down they have park rangers checking brake temps and I was one of the few that didn't get asked to pull over for a half hour to cool their brakes.

Does that help?

TheOtherEric

If you're slowing down to stop, then downshifting shouldn't have significant impact on fuel economy. The engine knows it's not under load and will shut off the fuel injectors regardless of gear.

That said, don't do it! Brakes are for stopping, not engines. I'd MUCH rather replace rotors than an engine or tranny.

mdreef

This is excellent feedback from everyone. Seems like I will no longer drive that way. I will use the paddle shifters to accelerate as intended.

Thanks again everyone!

Arrie

Not much and I disagree.

1. Transmission being on the "best" gear has nothing to do with the strain on the parts. The best gear is selected only for performance reasons. That is why there are so many gears and more coming on the later model cars.

There is a way you could cause extra strain on the transmission by down shifting too fast over several gears. Like with a manual transmission if at highway speed you go for from 5 to 2 or 1. This would really rev up the engine and possibly cause damage to it and also put extra forces on the gears in the tranny BUT I don't think this is even possible with our cars as it still is electronically controlled even when using the paddles. I think MB put some protection in place against this.

Also I think the OP was asking about slowing down using the engine brake instead of the brakes. I think he means in a controlled way like you would do with a manual car. This will absolutely not harm the power train in any way.

The wearing parts in the gear box are the helical gear wheels and bearings. These parts during normal operation almost always get loads on one side only. The other side gets loaded when reversing the car. When engine is used as a brake it is the same as reverse direction driving for the transmission, i.e. the almost never loaded side of the gear wheel tooth and almost never loaded axial bearing gets the load.

I don't know if you have ever seen insides of an old transmission. After 150 000 miles one side of the gear teeth look brand new, never used when the other side can be quite worn.


2. The OP asked if down shifting hurts the fuel economy. Sure manual driving can use more fuel but if you know how to do it, it does not necessarily mean that. I understood the question was if the down shifting uses more fuel and my opinion is it does not.

Down shifting can be used with automatic driving so that when coming to a stop you start using the left paddle to lower the gear and after coming to the stop hold the right side for a couple of seconds and it is on automatic again.

I would love to use the paddles but as slow as the gear changes are I find them useless. The only use I have for the paddles is to get the tranny to the right gear when I want to pass someone on a 2-lane road when holding the left side paddle for a couple seconds jumps the tranny directly to the gear that matches the engine speed for the best acceleration.

Arrie

Why do you think they included the left side paddle in the car? It is meant to be used to lower the gear if you want to drive in manual mode. When you drive in automatic the transmission still down shifts the gears when you slow down. It is no different than you doing it manually. It does it in very gentle way so you don't even feel it, i.e. not too fast but you can do this manually too.

Just go driving and let the car roll with foot off the gas and look at the rev counter and you will see how it changes the gears down.

In your normal city driving you are perfectly safe using the paddles. That is what they are there for.

El Cid

Today's automatic transmissions and computers are far superior to manual shifting, except in rare circumstances for acceleration.
It will cause more wear on your transmission and will cause more fuel useage.

hyperion667

so downshifting in my TT?it's a 6 speed

fintail

In my fintail, which has that antediluvian 60s era MB automatic, I downshift all the time, and often hold it in gear longer too, especially the change to 3-4 (both ways). The slowdown related automatic downshifts can be clunky, and it upshifts sooner than I would like. I doubt it causes any harm, other than wear on the linkage.

In my E55, I would downshift all the time, just to listen to the car, as it had a resonator delete and x-pipe.

In the W212, I find the paddles kind of silly, as it is a mellow Bluetec. I think I've used them once.

E Classy

You're fine. Just remember to rev-match using the gas pedal instead of slowly releasing the clutch.

It's much better for the OP to use engine braking if he is concerned about his brake system longevity. He will get better MPG while coasting as such - no gas pedal, no fuel injection, no burn.

SuzanOrtega

Agree with Live Oak completely. While many have different opinions, my take is to stay on the correct rpm and there should not be much to worry about. On another note, brakes are there to stop the car; the motor is to propel it.

ImInPA

Downshifting for either acceleration or to obtain engine braking for steep downhill grades is totally acceptable and safe. The procedure is described in the owner's manual. "rocking the transmission is also a function engineered into modern cars. The good news, all of the negatives that have been mentioned here are from a bygone era before the electronic controls. It used to be that you could shift a transmission into 1st or 2nd from 70 mph, not a good thing. Today's electronics prohibit actions that would cause damage. What a wonderful world.

CEB

Not quite. While modern electronics will limit the amount of catastrophic damage caused by over-revving, intentionally (and consistently) revving near redline to allow for engine braking is NOT good for the mechanicals - just like any extremes are bad for the car.

Modern electronic nannies are designed to keep you from over-revving when downshifting but once in lower gear, few will upshift fast enough to prevent over-revving on a steep downhill.

This discussion has been around for years and we'll see the same discussion here for years to come.

hyperion667

thanx for the reply sir

mtrevelino

With my 06 cdi it depends on how fast you are going for it to find the correct gear when you downshift. In my neighborhood, the speed limit is 25. Driving out of the neighborhood, I will downshift to 1st as soon as the car moves forward after backing out of the driveway, then hit the paddle two times to get it to 3rd. I keep it there until the last stop sign in my neighborhood where I will then hit the paddle a couple of times to get it in "D".
On my way back into the neighborhood, I wait until I slow down to 35 and hit the paddle one time, it will usually shift into 3rd, sometimes 4th if I am doing closer to 40.
I do this so that the transmission does not "hunt" between gears while in the neighborhood.
Again, depending on your speed when you downshift, the transmission should find the correct gear. It should not go into 1st or 2nd if you are doing 40 mph, but again, I never held the paddle to the left to see what will happen.
Mike T.

CEB

The electronics won't let you manually shift into a gear that will cause over-revving - but - once in that gear, the electronics may allow over-revving before it shifts out of that lower gear.

Arrie

My understanding is that the system protects the engine from over-revving at all times. If the gear is selected too low and the car is accelerated to red line it will shift up.