samsmart18

Well i am new to the world of owning an Audi A8 and so far i love the car!! However i have a couple of issues and i am unsure if they are related.

1) it overheated today. For a very short time. as soon as the warning light message came on i was pulling up to park anyway. sat there for 10 minutes and carried on and was back straight to 90 again on the dial. i checked the coolant and there pretty much was none left. I noticed that there is a sludge in the coolant tank? I topped up the G12 coolant and took it out for about 4 miles and was fine. Something else i noticed when i turn the car off there is a noise like air pressure being released from behind the coolant reservoir. Now the next thing is i know is to get the coolant drained and completely flushed and refilled but i was wondering what could have caused this? as i don't want it happen again! Behind the oil cap is fine no sludge and the dipstick is all good. Its had a oil change recently so the oil is clear. It doesn't appear that the coolant and oil are contaminating each other?

the 2nd issue is that the fans in the car blow absolutely fine. But i do not get any heat at all. I am unsure where to start on this one?

Any advise for a new A8 owner would be greatly appreciated.

Thank you in advance!

silverd2

The sludge in the coolant probably says it all (or most of it)...somebody screwed up and mixed the wrong coolant with G-12. Even a very small amount of ANY coolant (no matter what the label claims) added to G-12 results in a thick brown sludge that clogs heater cores and can eventually eat up plastic parts in the coolant circuit.

No heat could be a result of a still clogged heater core (USA model A8's with V8 have 2 heater cores...not sure about a 2.8 Euro?)...after a sludging event, the heater core(s) need to be flushed separately, at the heater hoses.

The coolant mix problem itself probably had nothing to do with the overheating...UNLESS it was in there long enough to eat up a fitting or jam the thermostat.

You likely have another problem that caused the overheating...maybe a bad cap on the reservoir (it would empty the coolant out behind the reservoir) or a cracked reservoir...both happen.
If you don't have a coolant leak there, then overheating is almost always the thermostat...these car are notorious for that. I was on my 3rd thermostat by 100K miles on the clock.

samsmart18

Thank you!

Here is my plan of action

1) get it chemically flushed through (heater cores separately too) ill update on here how many cores it has when i find out for other people's references!
2) replace the reservoir (have noticed it is wet around on surrounding pipes. Couldn't tell if it was condensation but probably not.
3) see how this goes and if still is a problem have a new thermostat installed.. I have a mountain of history with this car but cannot find a previous thermostat receipt and it has just topped 100k.

Hopefully this will solve my issues! Everything else with the car is as sweet as a nut.. I wish I could afford to run a 4.2 but with petrol prices over here I would never have any money!

Once again thanks for the advise!

samsmart18

Hi again,

The car has gone in today and they say I have a blown head gasket but they can't work out which one? As both sides are running so smoothly.

I have heard that head gasket issues are quite a common mid diagnosis? Is this true?

Thanks.

silverd2

I would want visual proof. Blown head gaskets are NOT a common problem in Audi engines...and easy to pinpoint: compression test, coolant mixed in oil, oil in the coolant, visual outside leak, steam in exhaust, etc...

You may have the wrong mechanic, if they could not describe immediate specific reasons for this diagnosis. Oil in the coolant would not appear as a sludge...it would bead up in small amounts and/or float on top of the coolant.

If they made their guess just because of the sludge in the coolant, they obviously don't know enough about these engines and the behavior of G-12 coolant. ...OR they are counting on you believing what they tell you.

Again, make them show proof of a blown head gasket, BEFORE starting work...or take it to another mechanic.