2.7T coolant leak advice...

[SLine04]

So the '04 A6 2.7T had a slow coolant leak for about 6 months. Looked and couldn't even find any drips under car but had to fill reservior occasionally. Few days ago while parked, found a puddle of coolant underneath. Could see the drips falling from rear of oil pan on passenger side. Put a drip pan under last night but it seems to have stopped, just a few drips in the pan. Reservior is down about an inch from minimum.

Did a bit of searching, seems it could be many things. Aux coolant pump under intake, cracked thermostat housing, elbow to heater hose behind engine for a few. Don't have garage space at the moment but did some looking. Looked in holes down through intake manifold with flashlight, couldn't see any coolant at all. Even poked a stick down where I could to see if it soaked up any coolant. Nothing. For those who have found leaky aux pump, was the coolant visible around the pump down there or could it be leaking even though I can't see any fluid?

Also, wouldn't a cracked thermostat housing continue to leak? I'm trying to apply some logic to figure out why it would leak constantly for three days then stop nearly completely. Maybe because it stopped an inch down from the minimum level on reservior that would point to something?

I ordered a coolant pressure tester kit so not going to do much more investigation until I get that but any input ahead of time is appreciated.

[C5S6]

Could just be the waterpump impeller seal has failed and it's leaking out the weep hole.
If your car doesn't have the metal tstat housing, now would be the time to get one if you've got to dig in.

[Calif_Kid]

I think that there is a coolant temp sensor (CTS) at the rear passenger side of the engine, so I searched for CTS and the thread https://www.audizine.com/forum/showt...?highlight=CTS mentions the CTS O-ring but also some other hoses that might leak, so take a look at the thread.

I've got a 2001 A6 with a 2.7T, and when I did my first timing belt, I upgraded from a plastic to a metal thermostat housing, but after around 7K miles, I had a slight coolant leak at the front of the engine, and it ended up being a slight leak from the O-ring that seals the thermostat housing to the engine, so this time, I used a tiny bit of sealant on the O-ring, and everything is leak tight.

- Jim

[oasis]

Coolant temp sensor gasket for me

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[SLine04]

Thanks for those responses. Local shop did the timing belt/water pump last year so I worried something might be wrong there. Not sure what thermostat housing or if shop replaced it, maybe I can check on it. But the coolant pressure test kit came the other day and I finally got around to using it. With about 10 lbs of pressure I hear hissing pretty sure from under intake manifold. Didn't hear anything near back or front of engine. But I still don't see any fluid down in there where aux coolant pump is even though it's dripping underneath by oil pan.

I'll get a second opinion as to where that hiss is coming from since my hearing isn't the greatest. If from the top, I'll start taking intake parts off to get a better look.

[Slave IV]

Looks like you are trying to figure it out yourself but unless you have the ability to really get in and check everything, might be better to have someone else with the experience take a look. My Allroad was down for over 2 years because of a coolant leak at the turbo lines. The parts are no longer available new so I had to source used ones and we all know how difficult it is to reach any of those turbo lines to replace so that's part of why I put it off for so long. This was all after replacing a radiator too.

[V1nny]

I think proper procedure is to pressurize cooling system to pinpoint the leak.

[aussieallroad01]

So the '04 A6 2.7T had a slow coolant leak for about 6 months. Looked and couldn't even find any drips under car but had to fill reservior occasionally. Few days ago while parked, found a puddle of coolant underneath. Could see the drips falling from rear of oil pan on passenger side..

Could be the heater hose elbow Oring since its at the back of the engine. I had this happen to me. Its a pain to fix, but doable.

[aussieallroad01]

see here: https://www.audizine.com/forum/showt...ts-leaking-now

[OOOOallroad]

Sounds about right for being the aux pump. I got lucky when mine started leaking 2 nights before I was leaving for the dragon. The impeller seal dried up and was leaking relatively slowly down the back of the block. I got a new pump from FCP and turns out the connections were different, so check for the correct one. Mine was the same as the injector clips but the new pump was different, swapping a new pigtail would be easy but I didn’t have any. I ended up just swapping the new pump side onto my old electric motor. Everything lined up nice and I was back to filling the coolant in no time. Good luck.
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[aussieallroad01]

If its aux pump you should generally be able to see pooling from the top side of the engine. Worth having a good look to try and narrow it down.

My preferred trick is to hose everything off as best as possible with a warm engine, let it dry it off, then go for a drive to see if you can see where the fresh leak comes from