MP4.2+6.0

Puddle underneath reservoir may be bad reservoir rather than any overheat. Over time we have had posts of both cracked reservoirs and leaking sensors at bottom of reservoir. Sensor is molded into the overall reservoir so not a separate part. But if it has low coolant from that draining down to sensor level, that should throw a dash warning and also kick in the jet engine fan protective mode.

ebi718

So, I did some further testing this afternoon. I opened the bleed valves (underneath cabin filter), gradually filled reservior to let out any air pockets, closed both and then ran heat on HI to get the juices flowing again. I noticed the fans were still going at full/high speed. (Ps: the spill yesterday was from the overflow line in the expansion thank - due to coolant level rising in the tank.) I confirmed that this afternoon.

Out of curiosity, I decided on another approach- take some readings off measuring blocks.



Most of the readings seem logical (given the fans were at full blast) but I don't get the -48 degrees C reading from 'Temperature diagnosis'. That seems out of range...perhaps a faulty temperature sensor? I had this same reading from a C5 years ago, and the ECT had to be replaced.

Ps: Strange that VCDS Autoscan is not reporting a faulty sensor; what am I missing?

MP4.2+6.0

Given that and fan jet engine classic symptom, yes do sensor. Cheap (like well sub $50) and known failure point with 4.2's. Just be careful on the mounting clip it uses--tie some dental floss to it so you don't lose it in never never world in back of motor. It is low down and buried, in back. Very low down. Some have posted on it. Did it on my C5 2000 A6 4.2 and still essentially same part and location as D3. W12 (also done) is in much harder location, but contrary to Bentley's step 1, pull motor (literally), a bunch of us proved out how to do it with a few hours labor. 4.2 is definitely in zone of a decent DIY'er w/ tools.

MP4.2+6.0

Given that and fan jet engine classic symptom, yes do sensor. Yes, it should have triggered dash light show and some codes, but whack temp reading and jet engine fan tells me at least some part of its electronic brains knows something is screwed up. Cheap (like well sub $50) and known failure point with 4.2's. Just be careful on the mounting clip it uses--tie some dental floss to it so you don't lose it in never never world in back of motor. It is low down and buried, in back. Very low down. Some have posted on it. Did it on my C5 2000 A6 4.2 and still essentially same part and location as D3. W12 (also done) is in much harder location, but contrary to Bentley's step 1, pull motor (literally), a bunch of us proved out how to do it with a few hours labor. 4.2 is definitely in zone of a decent DIY'er w/ std. tools.

Giovanni Giovino 6.0+6.0TT

Hello ebi718,


You say "Most of the readings seem logical (given the fans were at full blast)"
Yet your fans only show 52 and 58 percent, is that considered full blast ?


.

ebi718

Thanks; will schedule this weekend.
I am not sure if that's full blast....do you know? Please share if you do.