Hello MBWorld -

I have a 2015 C63S that has been experiencing rather high transmission temperatures. I acknowledge that these temperatures vary widely depending on conditions such as driving, and weather, but I was seeing temperatures of 250F+ during normal city driving (Comfort mode) and mild temperatures (high 70's F). No warnings came up and I shut the car down soon after this.

Wanted to get some input as to what types of transmission temperatures everyone else was seeing, and whether this was "normal". Planning to bring the car into the dealer for a check up, so if anyone has any ideas as to what might be causing this, it would be greatly appreciated.


Thanks in advance.

 

still in the "normal" range per that graph but mine has never gotten that hot. Maybe something damaged a cooler?

 

I watch mine, and it has never come close to your temps.
I get a normal temp of 183 deg and pushing hard in warm weather it only goes up 10-15 degs.

 

Your radiator/intercoolers might be damaged. I was experiencing temps like that (120+ celsius as I'm UK based) recently, as well as a noticeable power loss and slower gear changes (have you noticed any of those as well as the high temperature). Went to the service and turned out that a rock or some type of debris had hit and punctured my centre radiator. Had to get it replaced. They initially quoted £1300 for the part and repairs but my service contacted the goodwill team and they reduced it to £480.

Get it checked out and see what they find.

 

Yeah that's way too hot, and not normal. My trans temp won't go past 190ish even on hot 90 degree days with me driving hard.

 

Yeah that is not normal. The manual says 120C is the limit I think. Definitely a leak somewhere.

 

Thanks to everyone for your input. I figured that this temperature was outside of normal parameters. Will get it checked out and report back.

Trim - The shifting definitely got sloppier but I didn't push it hard enough to notice any performance loss. What I did notice was that the car sounded like a vacuum because it was working so hard to try and cool off.

 

Normal driving in Sport + and maybe high 70Fs ambient temp, I've never seen a trans temp above 190F.

 

Sounds about right. You've definitely got a similar (if not the same) issue to what I had. Get it checked out as soon as you can buddy!

 

Your second coolant tank might be empty so add some and bleed the air out.

 

Wanted to provide a final update to this post in case anyone experiences the same problem in the future. The issue turned about to be one of the transmission coolant pumps, which I believe is the part circled in the picture below. No leaks were detected and the coolers were in good shape, but the pump was operating sub-optimally, hence the slow creep in temperature. I worked with the shop foreman until we pinpointed the issue, then the part was replaced under warranty. Temperatures now maintain ~190 F, even during hard driving.

Thanks to everyone here for their input!

 

Glad it was covered under warranty for you (and not a damaged cooler)!

 

Good info for future reference.

 

I'm one of the unfortunate ones that had a rock puncture the front radiator. At first I didn't realize that's what had happened, and when describing the symptoms to my mechanic over the phone (high trans oil temp that just keeps rising), his first thought was exactly what happened to you. He said those pumps are pieces of crap and always fail. I wouldn't be surprised if as our cars get older we start to see more and more people with this type of failure.

 

 

I have a 2018 and also having this problem. Trans temp today went up to 258 F. I just scheduled a service to see what's up. Thankfully we have this forum because I placed two different calls to the dealer and NOBODY could tell me what the normal temperature range is for the transmission. I think MB needs to send them back to school or send out some bulletins.

 

After some back and forth with me insisting something was wrong, the shop finally identified a leak and replaced one of the circuit charge air coolers. They say it is holding steady at 185 deg. in Comfort mode. I will pick it up on Monday. It was covered under warranty. I found this forum extremely useful for learning that 259 deg is too high and for helping to pinpoint what I thought might turn out to be the problem.

 

1st. Check if you have coolant in the container between turbos, if not then you probably caught a rock on the radiator/which happened to me.
2nd. If you see coolant there, take it to the dealer for malfunctioning pump.

 

My temp sits at 177F... I thought that was the default setting for everyone as a little Easter egg 😂. Never goes much above 185F with aggressive street driving, and that's in Texas with 100F ambient temperature.

 

If you connect diagnostics computer and press on the gas, you notice that temp usually drops when you press on the gas. For me working temp for tranny is 84-86 Celcius.

 

Not to bump a dead thread, but what kind of damage do we think occurs if the trans oil temps get up to 250*F, albeit for a short amount of time?

 

Its not really an issue of how much time per say, its the REASON as to why, and when you get into HIGH temps, damage is already happening.

Fluid break down
sealant, seals, connectors start to breakdown/fail
electrical (some connectors are not made to deal with higher temps then others

The above is just a sample/example..

You also have to realize that something that is 250(f) (liguid) has the "wind chill" effect, as when its moving or being pumped around, it actually introduces a higher heat exchange and transfers since its generating more friction etc..
(so in lay terms, if its telling you 250, some of the components could actually be experience the effects of 300/400(f) and upwards )

So the question is, what happened or experianced prior to the high temps, that would be causing the high temp?

 

Very helpful answer, I appreciate it.

Two of the coolant pumps that help feed coolant to the transmission failed while driving and caused the trans oil temp to spike up to 248*F. I immediately pulled over and let the car cool down before bringing it to the dealership.

 

Good :-). would love to see pics of your ride :-).

 

Interesting, so both pumps failed simultaneously? Did you have any damage to the aux radiator or simply pump failures?