Coolant Temperature Too High Warning

[mattwez378]

Hi all,

Today while driving for about 20 mins I had the Coolant Temperature Too High warning come on the dash even though the coolant gauge was showing 1 bar (50C-55C), Oil temp was showing 75C. The car said to pull over and allow the engine to cool while running, I did pull over and check the coolant levels and for any leaks, no issues found. The fans were running at max speed constantly, even after turning it off and on again. The expansion tank was fairly cool and I would say coincided with the temp shown on the gauge, no excessive heat from the engine bay, so I carried on with the warning on to my destination approx 30mins further. The oil temp did not get above 80C and the temp gauge did not move from 1 bar, when reaching my destination I checked all the hoses I could see again and the coolant levels etc, nothing seemed to have changed.

After work approx 9hrs later (engine definitely cool) the warning came on after starting and the fans ran to max speed again. I drove home keeping an eye on the temps and the same was apparent as the journey to work.

Has anyone else had this issue? I have done some searching and seen other variants have had water pumps and temp sensors changed with the same fault being apparent afterwards, some have eventually been fixed by replacing the change-over valve (I don't know what this does?). Does the engine in the RS6 have this and if so would there be 2 of them? (1 for each bank?) or am I looking at a possible sensor or water pump?!

Is there any parameters I could check with VCDS? I have an old HEX-CAN cable I used on my 2012 RS3, I understand this would not fully work but it might give enough information to help diagnose a fault?

Due to other cars having an issue with the changeover valve which I believe is part of the vacuum system I am intrigued as to whether I have a vacuum issue as I had to change the brake servo sensor last week and this was the first longish journey since changing this.

Any info would be helpful as I cant seem to find any information on the C8's engine or parts for it, I will not be driving the car again until I have chance to plug it in (have to collect my cable from my brother later this week)

Thanks for reading!

[drhex]

Probably too late, had the same on a visit to Germany and got stranded at the Dutch border, Audi telling me that my mobility warranty had lapsed three weeks ago on a car with two years warranty left. Repaired the t-stat (which took them two weeks) under warranty, I paid the rental and chunnel. Annoying!

[mattwez378]

Hi drhex,

Yeah a little too late, however I have been meaning to update this post.

The thermostat has been replaced which took Boston Audi UK about 4 days once they got the part, so far no further issues with this.

The car is having some other electrical issues which Audi are in the process of looking at, so far a new boot lock and brake servo sensor… and it’s still showing an SOS fault which they haven’t looked at yet. Not great for a premium vehicle imo