Residue in coolant reservoir—what is this?

A6 All/ S6 All
#1

I was about to fill up with coolant after a w/p replacement and notices some discoloration, so I pulled the reservoir out to get a closer look. What’s going on here, guys?

http://audirevolution.net/addons/albums/images/899593

http://audirevolution.net/addons/albums/images/251745

Car has ~106k miles. The coolant reservoir was replaced at ~65k miles. No oil loss was noticeable. Not noticing any blue smoke at the tailpipe. Please tell me this is something other than a head gasket…

Suggestions for cleaning this out so I can get a good baseline going forward?

#2

and the pics…

http://audirevolution.net/addons/albums/images/899593898.jpeg

http://audirevolution.net/addons/albums/images/25174589.jpeg

#3

Oh, one more fact: the coolant I drained looks brand new, like its right from the jug.

#4

I lied. ;D One more piece of info: it’s like a thin, tar-like layer. Definitely not oil/brown milkshake like you’d see from a head gasket.

#5

Didn’t you say you had a failed oil cooler. You might have gotten oil from that into the coolant system. The specs in the pictures almost look like broken down gasket of some type I can’t really tell from the picture. usually you would rule out just plain dirt as dirt would settle in the rad unit. the only other thing I can think of that looks like that is total seal. its a substance you poor in the rad unit to plug holes. Total seal collects in the coolant resivware like that.

#6

Justin, good memory and that makes total sense know. The residue is kind of rubbery.

How should I flush this out?

Should I buy another reservoir?

#7

Hmm, but thinking it through, the two rubber seals that seal the oil cooler to the side of the engine block are exposed to oil only. So any failure of those seals should not result in seal material into the coolant.

With that said, it does appear to be some break down of rubber material. Maybe one or more coolant hoses are degrading? I wiped the inside of the coolant hoses out before I reassembled everything. One or two of them did feel a bit rough and grainy on the inside and like the material was coming off. Perhaps an early indication of a hose failure?

#8

Had the same sort of residue in my coolant tank before replacing it.

Was not expensive to replace, so I’d think about that. I had a few cracks in mine that allowed air to get in the system, so worth noting that in your inspection.

I did not notice anything out of the ordinary while taking my car apart to replace my radiator, but I think that could have been some sort of additive that people add to stop leaks.

#9

Interesting. I had my radiator replaced at about 70k miles after hitting a deer. This was after putting in a new reservoir because the old one was cracked. Anyway, no real damage from the collision (had hood replaced and bumper repainted). I wonder if the collision shop puts in the additive as a preventative measure after taking apart some of the coolant system. Would make sense I suppose.