A6 Overheating

[ostinpawas]

Help.A6 avant on 53 plate(UK) just out of warranty(by 5months)..overheated yesterday on motorway(light traffic..free flowing at 70mph)..got red coolant temp/quant warning so stopped immediatley and got towed home.
Replicated the problem today by driving it for about 15 mins....fans all work etc...temp stabilised at 90C then suddenly and quickly went to 120C with warning...when car stopped temp decreased v. quickly to 90C (with fan running too).
Observed coolant reservoir bubbling..in fact it bubbles into the overflow underneath...
Can anyone help me please?

If it is thermostat related..where is it and is it a big job?
edit...A6 Petrol 2.0Litre Avant SE

thanks guys

Ostin

[a6kerry]

hi ostin.
is the heater still getting hot?

kerry

[ostinpawas]

I have just run the engine ..it gets to 90C on the water guage but the heater is not hot.............

What does that mean?

Can you also advise which oil I should be putting in the A6 Avant 2.oL petrol engine?...I was putting a very very thin fully synthetic oil in but it goes through it like there's no tomorrow...any ideas


Thanks for your help

[buster]

Help.A6 avant on 53 plate(UK) just out of warranty(by 5months)..overheated yesterday on motorway(light traffic..free flowing at 70mph)..got red coolant temp/quant warning so stopped immediatley and got towed home.
Replicated the problem today by driving it for about 15 mins....fans all work etc...temp stabilised at 90C then suddenly and quickly went to 120C with warning...when car stopped temp decreased v. quickly to 90C (with fan running too).
Observed coolant reservoir bubbling..in fact it bubbles into the overflow underneath...
Can anyone help me please?

If it is thermostat related..where is it and is it a big job?
edit...A6 Petrol 2.0Litre Avant SE

thanks guys

Ostin

Could be a simple as a split or weeping hose. There are rather a lot of them on the A6. When you refilled the radiator, you may have left some air trapped in the system which would expand very rapidly and blow all of the water out. When you refill it again, make sure you bleed the water system. I had a Montego once which just blew all of the water out, but when refilled and bled, never did it again.

Do you have access to a kit to pressure test the radiator and water system? If not it would be worth taking it to a garge and ask them to do it.

It could be the thermostat sticking. This is supposed to open when hot to allow the water from the engine to be cooled by passing through the radiator. If its not working, the engine water will keep getting hotter until it boils and blows itself out of the header tank.

Worse case scenario - head gasket gone - <tremble>

Worst case scenario - cracked head - <big tremble>

[a6kerry]

hi ostin.
without looking at it i would agre with buster it sounds like its got an air lock i would start by replacing the thermostat and giving it a bleed then see how it goes. i would of thought fully synthetic oil was to thin for your engine semi synthetic should be more than up to the job. but you could
phone the main ******** to make sure.
cheers kerry

[guyg]

The symptoms [90+C no heater] sounds like no circulation -

1. Airlock
2. Bust water pump.

I'm not sure about your A6, but a lot of VAG engines have a pump with plastic impellers, which either become loose on the shaft and only spin when they feel like it [or not at all!] or they break up.

If you take a hose off, you should be able to get finger down the opening [WITH THE ENGINE OFF!!!] and feel if the impeller is attached and intact.

If the temperature stabilised at 90 before climbing again, the stat is probably working.

Cheers,

Guy