c4S6

So, my car has been running great and the cooling is always fine. Then, last week, the plastic T-fitting at the back of the block broke (see photo below) while I was driving it and caused all the coolant to exit quite fast. Luckly, I was close to a safe open lot. Ordered the new part and replaced it a day or so later.

Added new coolant (Sierra phosphate free), and water. And, yes, I used proper Distilled Water, bought from the store. Filled it, ran the engine, let it warm up and the thermostat to open up... Then, once it was warm and temp guage was at halfway, I turned on the heat full blast to open up the heater core. This is, what I've always been told is the best way to bleed out the cooling system and make sure there is no air trapped.

A few days later I check it as it commonly will need to be "topped up" after a full drain, and I find this brown "gunk" in my coolant reservoir at the top, kind of forming a line where the coolant sits. This was all stuck to the reservoir and at the top (not actually getting cycled through the coolant anymore).

<img src="http://www.s-cars.org/postnuke/modules/gallery/albums/danh/IMG_3744_001.jpg">

<img src="http://www.s-cars.org/postnuke/modules/gallery/albums/danh/IMG_3745.jpg">

So, my question is... for those viewing the pictures... What is this? And, is this something that got flushed out from my heater core when I did the full bleed??? I assume that is what this is, and that I just need to drain the reservoir, clean it out, put it back on and top it off. Go about my business.

But, want to make sure this is not a sign of anything amiss with my car.

I can say that the coolant was replaced about a year and a half ago, and it was perfectly clean (looked like new) before my car lost that T-fitting deal, so, I don't think there is any existing issues.

Any input appreciated.

Also, as you may notice... I've added some flourescent lighting in my garage and it's like AMAZING! I can see like 100% better. It's wonderful!

Also, a PSA to everyone with high mileage S4/S6 cars (which is just about all of us except Tom (90Carrot)), replace your T-fitting, or it will end up like mine...

<img src="http://www.s-cars.org/postnuke/modules/gallery/albums/danh/IMG_3758.jpg">

quattro20v

Looks like it may be engine oil mixing with the coolant, which can be caused by a blown head gasket. Check your dipstick to see if you see if the oil is light brown color, if so, your head gasket has likey failed.

c4S6

I'm not saying it isn't possible, but I doubt this is the case. I never had it before until I flushed to coolant with recent cooling system leak. Car runs awsome, AND my head gasked was replaced a few years back once already. These new copper head gaskets don't seem to fail commonly.

I noticed it right after I put in new coolant after a full flush and haven't seen any additional "gunk" since. I'm thinking I will simply drain the coolant out of the reservoir, clean it out, and refil. It isn't easy to clean out these reservoirs, however, as you only have that opening at the top and a small one at the bottom.

SchwarzS6

Sounds like motor oil to me also, what you show is exactly what it looks like. It is possible that the reason the T fitting failed was that it was weak and a leaky head gasket caused excess pressure in the cooling system. Like Quattro20V said, look at the engine oil and maybe do a compression/leakdown test.

MA_2.7t

According to audi releases, their mixed coolants turn into brownish sludge. If you JUST switched its possible you some leftover which mixed.

UrSobsessed

perhaps you didn't flush as well as you needed too. i've heard of guys running the engine and flushing for 30 min.

MrDDD

I'm with UrSobsessed!

It looks like the brown gunk you get when mixing G11 and G12 coolants.
(No I did not do that. The fine mechanic who did my headwork did)

c4S6

Just checked my dipstick. Oil (which was recently changed as well), is clean as a whistle. No signs of coolant in the oil, which is good.

I'm going to clean out the reservoir tomorrow and refill and then keep my eye on it.

It was a little bit low, which I think makes sense. I think after a full "flush" it will accept more coolant as it fills in the voids and need to be topped up anyways.