ajskyman

Today I was helping a buddy of mine replace his thermostat on his 1993 S4 in an attempt to solve an overheating issue. The housing came off easily, yet the thermostat was very difficult to remove, as if the old thermostat gasket had fused to the block. With some carefully applied force we were able to remove it and insert a new one which seated easily. Yet with the new thermostat and accompanying gasket installed, we quickly found that there was coolant leaking from in-between the housing and the block at a moderate rate (5-7 drips per second could be seen under the car) when the system is pressurized. A secondary tightening seemed to slow the leak, yet it is still very much there. The new thermostat is an OE Stant with a gasket to match by some other brand.

Due to the age and mileage of this car (280k) I am unsure if there should have been a gasket between the housing and block (there wasn't one when we removed the housing), or if there is another issue.

I see that new housings are around $10-$20 online and are now made of plastic. Could it be that a new housing is needed? There are no obvious signs of cracking or damage on the original housing.

Any input is welcome.

Thanks!

UrS4boy

Theres is only one gasket. Did you clean out the "boss" in the block that receives that gasket? Could be the issue. Also the gasket (aka "round seal - 60 x 3.5") itself could be too thin. Recommend getting one from a dealer to make sure that it is the right one.

Go to this link and click on the thermostat label (all the labels are live links so you might want to book mark the link for future reference):

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

ajskyman

Thanks so much for the fast reply, we will give it another try this weekend and I'll report back with the results.

UrS4boy

In the meantime, get a proper N 9013682 60 x 3.5 round seal.

ajskyman

Today we dove back into the car and inspected the thermostat housing, and it looks like we've found the culprit of the leaking.

The stock plastic thermostat housing deteriorated where it touches the thermostat gasket. Image attached. The part has been ordered (no parts store in town carried the housing) and will be here around Tuesday. I will post another update when I have time.

Thank you for all of the useful information!

UrS4boy

Yep. That would do it. A wrecker might have a metal thermostat housing from an Audi 5000 or 200.

For more thermostat info, click on link below and then on the thermostat label on the lower right side of the diagram (all the labels are hyperlinks so it's a good one to book mark for future reference)

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html



Here is a close up of the 034121121A metal thermostat cover. The 035121121A was never uses as an UrS4/S6 AAN thermostat cover but it was on a wide range of Audi engines including the WB, WC, WE, WG, KU, NF, KU, HX, PX and MC, etc.

GoHeels

...and if money is no object, you can buy 1 from a store in California.

Timberjo1

Hey, I'm the "friend". So we ended up needing a new thermostat housing. We got that and installed it but it is still leaking. Not nearly as much now, though. I think the problem may be that I can't tighten the top bolt that secures the housing as much as it needs to be and hence is creating enough of a lack of seal to create a leak. So I guess the next step would be removing the whole intake etc. to get better access to the bolt. Is there a good tutorial showing how to remove it all?

UrS4boy

Removing the intake is a lot of work just to replace the thermostat and housing. I am working on said "tutorial" but I am lost on a basement reno project so it won't be there in time for your needs. (I am replacing the injector inserts).

If you followed my DIY in the link I posted above (and again below), you will find this phrase "With whatever combination of stubby rachet, extension, universal joint, 10 mm socket or 10 mm wrench (check - this is from memory), loosen the two bolts holding the T-stat housing to the block." The key is there is a combo that will allow you access to those bolts. Definitely disconnet the intercooler to throttle body hose and shove it out of the way so you can get at the thermostat housing easier.

You might have to use a Scotchbrite pad or something to clean off the block where the thermostat sits before reassembling.

For more thermostat info, click on link below and then on the thermostat label on the lower right side of the diagram (all the labels are hyperlinks so it's a good one to book mark for future reference)

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

Timberjo1

So I followed your advice and decided to remove the thermostat and housing and cleaning the mating surface (which actually was quite dirty). One of my friends also recommended that I apply some "sealant" the rtv type that comes in a tube. So I got the surface really clean using a rough sponge pad a very fine grit sand paper and then applied that and put it all back together. I had a really good feeling about it. I let it sit for an hour to let the sealant cure and then tightened it all down. I ended up buying a longer extension 14" I believe and a jointed 10mm socket which let me get a lot more torque down on the bolt. It all felt good. I started to fill it back up with coolant and almost immediately it started leaking again, and this time worse than before. I'm not sure what I did wrong. Was the sealant a mistake? This car will just not give up! Any help is appreciated, thanks.