I saw this on another forum

[Tazz666]

I was trawling through another forum and I came across this bit of information and I was wondering if this was correct?

Bobabenz is right. Its a soft rev limiter that is set just above 4k when the vehicle is in park or neutral.
I am sorry for seeming a bit thick and asking what may seem stupid questions but this is my 1st Mercedes and I want to learn as much as I can

 

[kth286]

It is correct for mine, there IS a rev limit in neutral/park.

 

[John]

Yes - mine refuses to rev passed around 4k in neutral.

I presume to prevent overheating.

 

[Tazz666]

Thanks guys I tested it out today and it does do it, If I never came across this, I wouldve thought that there was something wrong with my car

 

[Howard]

Why would you need to rev it past 4k in neutral / park ?

 

[CubbyMK]

Why would you need to rev it past 4k in neutral / park ?

to look "cool" ..... dude.

 

[rf065]

Yes - mine refuses to rev passed around 4k in neutral.

I presume to prevent overheating.

More likely to prevent engine damage as the engine is not under any load.

Russ

 

[Tazz666]

Why would you need to rev it past 4k in neutral / park ?

just to cure my curiosity to see if it was true or not

 

[ShinyF1]

A friend used to do it in his Dad's new 420SEL then put it into 'D' just to see a big new S Class snake off the line. Not sure the old man ever knew what he was up to. Teenagers, eh?

 

[Deleted member 6183]

Why would you need to rev it past 4k in neutral / park ?

To break a company car that you hate and want rid of.




Well, it was 20 years ago.

 

[sinewave]

to look "cool" ..... dude.

Depends whose watchin'!

Most would assume you were a Grade 1 C0CK!

 

[John]

Why would you need to rev it past 4k in neutral / park ?

I've done it once or twice to demonstrate the sound to someone else.

 

[Howard]

Me too , but never needed to rev it that far

 

[John]

You can't anyway but given how hard these cars can be driven (I'm talking about mine), even if it could be rev'd beyond, for a second or two on a warm engine is not going to be a massive problem for it...

 

[Howard]

Turn your speakers up tee hee

100_4555.mp4 video by howardmiatt - Photobucket

 

[rf065]

You can't anyway but given how hard these cars can be driven (I'm talking about mine), even if it could be rev'd beyond, for a second or two on a warm engine is not going to be a massive problem for it...

I think the piston slap & valve bounce from the engine being revved without being under any load would be a problem, why else would Mercedes see fit to further limit the revs when in neutral? Being driven hard is not the same thing as being revved high in neutral.

Russ

 

[John]

Turn your speakers up tee hee

100_4555.mp4 video by howardmiatt - Photobucket

I was waiting for something to pop there...

I think the piston slap & valve bounce from the engine being revved without being under any load would be a problem, why else would Mercedes see fit to further limit the revs when in neutral? Being driven hard is not the same thing as being revved high in neutral.

Russ

No, but if you sat there revving at 7000rpm relentelessly, I would expect an issue. Not the odd couple of revs beyond it at idle...

 

[rf065]

No, but if you sat there revving at 7000rpm relentelessly, I would expect an issue. Not the odd couple of revs beyond it at idle...

The problem with engines at high revs is harmonic vibrations which can cause damage to the crank, pistons or valve train. When an engine is revved under load these are somewhat evened out and less of a problem. When not under load they can cause serious damage.

I personally would not dream of revving an engine to the rev limiter when in neutral. Mechanical sympathy would prevent me from doing so.

Russ

 

[ivan1983]

Im not sure why anyone would want to rev an engine in neutral that high. Im happy to take an engine upto the redline on the move once warm though.

I thought the torque converter spins with the engine? If thats the case then revving in neutral would cause the ATF to get too hot.

Generally they put a limit on for a reason

 

[John]

I've no doubt they wouldn't bother with it if it wasn't necessary but I've seen launch control (can't remember on what) where it rev'd up to 5000 > 5500rpm before take off.

Admittedly, some are capped at 4000rpm, but given the frequency someone with that kind of car is likely to use it (i.e. a lot more than a few errant idles), I would have thought manufacturers would be a lot more paranoid about setting the rev limit too high for that.

I've not heard a manufacturer not warranting the engine with launch control - only the transmission which of course we are not talking about here...