Hi,

Was at Wakefield yesterday, first time with the Evo rear rotors and Titanium shims. It was 38c so not that pleasant .I was wondering if any
of you have experienced the auto going to Comfort from Manual which happened every run after a few hot laps M could not be selected until approx 30 minutes after coming in. Mercedes are checking around to see
what is the cause, I would imagine it is a heat issue with the sensor and computer. Received call from Mercedes as I was typing this post, they want the car for 1/2 a day so can find the cause.

Thanks

Ian Shuttle

 

I've had the same thing happen to me on the track. It's the transmission approaching damaging levels and basically locking you out of M mode until the temps lower. The first time it happened to me I was at triple digit speeds in the middle of a high speed right hander in 5th gear and it kicked me out of M, upshifted to 7th, threw the car all out of shape and I almost lost control of the car and nearly had a BIG off. Not cool.
I'm sure your dealer will come back to you and say the trans was overheating and protecting itself from damage.

Keep us posted please.

 

Watch your engine oil temp, when it goes above 135c, bang, down to C you go.
It keeps you there until the temp drops to 130c.

Make sure your AC is off, the car runs cooler that way.
Yes, it's happened to me, busted into C looking around and wondering, "WHAT THE .... Oh."

Other times it was just that hot on the track 38+, happens more easily in M.

Don't let the dealer have your car to test that out!

 

My dealer said the same, but why would it change transmission modes? Is that a different limp mode ? When it happened to me as described above, I instantly mashed the gas to get the rear end to grip and it downshifted and was back at redline...albeit in C mode. Point is, I think it has more to do with trans temp than engine oil temp. Engine parameters being exceeded will cause limp mode - this trans shutout thing is strange....but as I work on the car more, the more I realize that they are so limited production and they all have very different characteristics that the factory really didnt bother putting in the manual. They just did it knowing that not too many people would ever really figure it out nor would they have to explain it - other than a dealer tech noting, "no problem found - could not be duplicated - normal operation".

 

I think it's exactly as you put it, "a different limp mode".
It is effective though at limiting risk to the engine. It seems they've determined that 135c/275f is the high side for oil temp.

 

I had a discussion about this with my shop foreman as my oil temps seem to run high on a normal basis. But, I only drive in M mode and use the gears alot around town usually never getting out of 3rd - so, I see high revs constantly. Anyway, this was his response to oil temps:

"You oil temp doesn't seem out of line. the oil has to run over 100C to prevent any moisture from building up. On a race track outing somewhere close to 150C (300F) is possible. 175C (350F) it's time back off!!! The flash point of the oil is 224C (435F). You definitely don't want to go there even though the manufacturers claim protection to 400F !! The oil won't last too long at those temps. A non synthetic oil is done at 350F, it starts smoking."


I think you're right about the 135C/275F point being the cars preset limiter throwing it into limp mode to protect the motor. Knowing that and with the above quote just confirms again how conservative AMG is with their calculations and limits...once again, favoring reliability over all out performance. That's the reason these cars will easily run 200k miles in stock form.

 

My car did the same to me the first, and only time so far, I had it at the track. It was especially off putting since the ambient temps were mild; (the 70Fs), and the engine oil temp was below 120C.

This has to be a temperature modified 'protection' feature for the transmission imho since when it happened to me, the engine oil temp as I mentioned was fine. What I believe is happening at least in my experience is that in 'M' mode on the track, I am staying at much high revs in lower/middle gears than you would normally see on the street. This is leading to much higher temps than the transmission ECU would normally be seeing, as the transmission is not being allowed, (deliberately), to change up. Doubt there's any way to correct this other than installing a larger than OEM transmission oil cooler.

My second and subsequent runs I stayed in 'S' mode, and never had any issues, even when the revs were staying up much higher than you would see in 'C' mode. I hated not being comfortable staying in 'M' though.

Any other thoughts?

Bish

 

That's odd - low ambient temps and you went into limp mode right away ? Which track ? I can see that happening on a very short, tight track....perhaps there's some further adaptation parameters kicking in that sense you never using M mode ?? No clue...I've had my car on track many times and only when it was 118 degrees ambient on Streets of Willow did it ever go into limp mode and on that track you never get out of 3rd in the BS.

 

This sounds surely like a transmission temperature issue rather than the engine surely? I've never witnessed anyone fry the engine of a modern high performance street car on the track that was unmodified. Brakes and automatic transmissions are the fail points unless you guys know something about the 6.2 that I should be made aware of.

 

Heartland Park in Topeka, KS. Not a particularly tight technical track either. There's decent straights with enough time to keep things cool(ish). I was surprised when the car did it to be honest. I hope it isn't something that continues later on this year when the temps start to climb.

Bish

 

Hi
Thanks for the replies, Will know more on the 9th Feb, I didnt check the
engine oil temp though would have been high, I dont mind the car protecting itself though can be very distracting on the track.

I will be pushing for a higher grade oil for the motor and transmission or bigger cooler as most of my track days are on a tight track and never go over 4th gear. Maybe the computer can be programmed up, though Benz
are more than likely not willing ,though no harm in trying

Will let you know their reply.

Regards

Ian Shuttle