2018 Model S "oil in coolant"

[ucmndd]

Is it possible its dripping due to moisture?

Yes, of course.

The difference between water and coolant is very obvious.

 

[Jonnymack74]

Yes, of course.

The difference between water and coolant is very obvious.

Ok so this puts my mind at ease somewhat. Next question is why would tesla service just say 500 quid and not suggest it could be due to air con? I've followed up to ask direct via the app so will see what they say

 

[TLLMRRJ]

A failure (such as an internal leak) of a heat exchanger could explain the contamination of the coolant by automatic transmission fluid. However, according to two different workshops, no failure has been identified, and this hypothesis seems unlikely;

Did they ever take samples of the ATF fluid in both your drive units and have them analyzed for coolant contamination? That's something that Blackstone Labs does as a routine test.

I know they said the two different workshops didn't find a failure that would cause this problem, but how did they check? Sorry to say, shops are filled with lazy, untrained, and disgruntle mechanics these days, so they don't always work hard to find the root cause of problems.

If there was coolant in the ATF fluid, then you would know that cross-contamination was the issue. There are other seals that can fail besides the heat exchangers that can cause cross-contamination.

It would also be interesting to pressure test the coolant system for a long period of time to see where your coolant went. You had low coolant, so it went somewhere. I would drain the ATF from both drive units, and then use a coolant pressure tester to apply the max rating pressure of the cooling system overnight, and see if any coolant comes out of the drive unit ATF drain plugs.