c5 RS6 overheating problems

[oldboy]

Hi - am new to the forum. And looks like this might be my best bet as seems to be a lot of knowledgeable people on here! Certainly don't trust Audi main dealers anymore.
Got an overheating problem.
In drive temp gauge will drift up to 105 mark and unless I change into sport mode and boot it to raise RPM to 4000, will set off temp alarm.
As long as I maintain between 3-4000 will stay under 105 and keeping at 4000 will bring it down to normal.
Had her decatted and retuned by Doug at MRC 6 weeks ago but can't see that that would have anything to do with it - from 480 bhp to 520 ( already had "usuals" from Unit 20 - Wagner intercoolers, Miltek catback, Hopkiss ARBs - when I bought her back at Christmas ).
Hope someone out there has come across this before.

[bakustax]

The gauge should read a steady 90...105 is too high...usual suspects would be thermostat and dodgy temp sender...my money would be on the thermostat...I think the booting to get the temp down could be airflow from increased velocity bringing the temp down!...the easiest way to tell if your thermostat is AWOL is fans continuing to run when you've parked up and shut the beast down.

[oldboy]

Thanks for your response, but the problem is rpm and not speed related, so if I keep it at 4000rpm in a very low gear at a very slow speed, it's fine. You'd expect it to overheat in traffic as the engine is working harder than it needs to but it seems fine - which makes me think it's not thermostat. I'm thinking some kind of relay/fan switch but don't know enough about the cooling electrics set up.
Anyone out there knows how it all works on the cooling front?

[Shoppinit]

I had this once with another car. It was driving me mad. At high RPM it would cool OK, at low rpm it would start to overheat.

Turned out to be a worn water pump.

I still think it's your thermostat, but since you change them both at the same time, that is where you need to be pointing your wallet.

That's assuming that you've made sure your fans work ok.