GeoS4V8

Just changed the oil in the 97 A4 to 0W-30 Mobil 1 and reset the service indicator with the VAG-COM. All set for the winter. Anyway, while poking around under the hood I noticed the coolant reservoir in our 1.8Tq looks brown. When I pulled the cap off there was some frothy brownish (terra cotta) residue on top of the cap. I pulled some fluid out and it is still pinky but the plastic reservoir is coated in this brownish film...like rust. So the entire reservoir looks brown because of this film. I read that the fluid is good forever but it looks to me like it needs flushed. Should I? Has anyone ever? How do I? Should I buy the OEM stuff or is it OK to mix? Anyone else have this? The car has 67,000 chipped miles on it, and I am the original owner.

Typist Formerly Known as (skene)

time to flush out your system....

dingster

It's normal for our cars. When the red stuff dries it gets like that. When the engine is hot, some coolant vapor gets on the top side of the expansion tank and dries to that nasty stuff. Over time it accumulates and cakes up. It's perfectly normal and won't cause any harm(just looks ugly).

I suppose you can flush you system but it won't get rid of the residue. The fluid should be good for 100K+. Whatever you do don't mix it with any other kind of coolant. Only use VAG G12 or else you may do damage to your engine.

Bryans12v

Go pick up about 4.5l (3 bottles) of the G12 coolant and abot 5 gallons of distlled water.

Drain all the coolant from the red plug at the bottom right-hand side of your IC. Take a running hose and stick it in the resivior with the plug open and run the car in this fashion for about 3 mins. Let it all drain.

Then close the plug and fill with the distilled water. Let the car run in this fashion for about 5 mins. Drain all the water, and fill with the distilled water and the G12 coolant(50/50).