View Full Version : sludgy coolant?!?

04-29-2012, 01:31 PM
i got an issue, bought a b5 a4 1.8t about a month ago and i noticed that the coolant isnt clear like its suppose to be. it looks like nesquick milk shake lol....my boy and i think it could be the oil cooler. anyone else ever have this issue?

04-29-2012, 02:44 PM
Do a coolant flush with new reservoir (you could be seeing things). If the fresh coolant gets milky, I would look into the o-ring on the oil cooler first (like a $3 fix). If it isn't that, could be the HG. But if you don't have low cylinder compression, I would rule that out.

04-29-2012, 02:51 PM
Iight thanks, what's Hg?

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04-29-2012, 02:56 PM
Head gasket

04-29-2012, 03:05 PM

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04-29-2012, 04:14 PM
eh as seerlah said, on almost every other car this would mean blown headgasket.

BUT, replace that o-ring first.. if its just that I will be very surprised.

04-29-2012, 06:06 PM
PO could have used wrong coolant maybe, not g12. I've read a few threads on here of the oil cooler going and mixing oil/coolant.

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04-29-2012, 06:36 PM
I'm thinking of replacing it... $108 Jhm website

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04-29-2012, 06:41 PM
check oil cap and see if oil looks like crappy goo.
i would check compression and hope it's good
replace oil cooler o rings
check oil cooler for leakage
flush coolant
put it all back together and hope for no sludgy goo

is this what you have going on?

04-29-2012, 06:53 PM
Yea definitely,

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04-29-2012, 06:56 PM
Hopefully it's just the oil cooler mate!

04-29-2012, 07:07 PM
Yea i'm going to order the cooler tomorrow, put in flush system and then report back

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04-29-2012, 07:08 PM
How can I flush all the goo out?

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04-29-2012, 07:37 PM
flush the whole system .. hose at one end . turn it on full flow.. pump water through the whole system..

04-29-2012, 08:10 PM
Just to clear things up: failure of the o-ring on the oil cooler cannot cause oil and coolant mixture. Can Not. The o-ring only seals the cooler to the oil filter flange. Failure of this oil cooler o-ring would merely cause an external oil leak (and usually a pretty big one). No other failure can result (save the resulting oil starvation and complete engine destruction, minor things really).

That o-ring in no way keeps oil and coolant separate. That is the job of the aluminum oil cooler itself. If oil and coolant are mixing due to the oil cooler system, it is simply a failure of the cooler itself.

If one suspects an oil cooler failure, due to mixing of oil and coolant, one can verify this in 1 of 2 ways.

1. Buy a new oil cooler and cross ones fingers that you didn't waste your money.
2. "Loop" the oil cooler's coolant lines. This bypasses coolant flow through the oil cooler completely. If oil continues to mix with coolant after the bypass, the problem is elsewhere (head gasket, cracked block, turbocharger, etc. Most likely being the head gasket).

04-30-2012, 03:23 AM
Walky_talky20, very informative. and yea My fingers are crossed lol.

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04-30-2012, 06:23 AM
Also surprised no one has mentioned mixing coolant yet. When you mix G12 (pink) with regular parts store propylene glycol coolant (green) it creates a thick nasty mixture like that. I would start with a good coolant flush and see if that helps before you start replacing parts.

05-01-2012, 06:49 PM
walky is correct the oring doesnt cause this. Actually just worked on a v6 passat with the same exact problem and was a bad cooler. its also abitch to clean out, flushed it 3 times and still crap in the system

05-01-2012, 08:14 PM
Damn for real? My boy was saying there is some thing made by Preston that's for flushing out the system odk I didn't look into it yet

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05-02-2012, 03:09 PM
You can pull the cooler off, then pressure test it on the bench. Block one port, pressurize the other with a few pounds of air controlled on a regulator, listen for a leak.

My pin hole leak was emptying my oil sump into my water system. The oil ends up floating up into the reservoir. After replacing the cooler, I ran the system filled with water + citrus degreaser solution. It took 2 weeks of flushes draining the solution daily. Once it looked clean, I started flushing the system with distilled water for a week daily. Then I refilled the system with coolant/distilled.

The oil/sludge works into the rad and heater core pretty good. The first few slushes are pretty sludgy. I ended up changing out the reservoir/cap as well, mostly because it was yellow and disgusting.

05-03-2012, 02:33 AM
You didn't drive around with the citrus degreaser did you? And i'm guessing I could get that at a parts store

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05-03-2012, 12:57 PM
walky is correct

DUH!! lol

Regarding the coolant mixture: Here is a thread that someone did an experiment on a while back. In summary, only use G12 and NEVER mix coolants.

Hope it works out for you!

05-03-2012, 03:16 PM
Yes I did. It cleaned the system up nicely. With the new reservoir, there were no signs of oil residue at all. As the system got cleaner I diluted the degreaser mixture. It stayed oily and translucent for quite a while. You just have to get into a rhythm of coming home, opening the petcock, drain the fluid, refill with new. Do this every day, and it finally begins to clean up. May be a cold water flush from your garden hose would work, but mine worked well. I'd be confident of doing it again. My coolant looks brand new and uncontaminated now.

To give you an idea of how oily my mess was, I had raw oil in the reservoir, and a cream of mushroom consistency of oil in water gel coming out of the petcock on the rad.