Thermostat DIY for b6

**R&Cs4** · 12-01-2009 05:53 PM

Ive searched and I cant find a diy for a thermostat. anyone have a link to one? anyone have experience with doing one...how difficult is it? TYIA

**outkasta4** · 12-01-2009 08:11 PM

Here you go http://www.audiworld.com/tech/eng.html go 9 down

**R&Cs4** · 12-01-2009 08:20 PM

i need it for a b6 S4, not A4

**littleredwagen** · 12-02-2009 05:16 AM

to access the thermostat on an V8 S4 is simple. I dont have pics but it is done jacking the car up and removing the belly ban. then look for the lower radiator hose on the drivers side it goes into the water pump on the front of the engine. unclip that hose, there are 4 inverted torx head bolts that secure the water neck/thermostat housing to the water pump , remove them and the thermostat is right there it can be replaced. you will have to drain the coolant, so have a clean bucket so you can reuse it. on the bottom of the water neck/thermostat housing you will see a drainplug that is how you drain the coolant. there also might be a hose going into the top of the housing you may not need to remove it though.

**szinkuti** · 12-02-2009 07:35 AM

Its 4 bolts...they are female torx....i believe 8's and you replace the housing with thermostat as one piece....gravy

**R&Cs4** · 12-02-2009 09:35 AM

wow this seems alot easier than i thought...on the 1.8's it looks like you have to remover the alternator and such. thanks for the help. how hard is the belly pan to remove on these cars?

**ngng** · 12-02-2009 09:42 AM

I replaced the thermostat and gasket at 45k, the unit looked like it was in great condition

**psiaddict** · 12-03-2009 06:43 AM

I believe there are 2 thermostats on these cars, the main thermostat and the secondary cooling thermostat. Just FYI and sorry I don't know where the second one is.

**littleredwagen** · 12-03-2009 07:23 AM

Originally Posted by psiaddict

I believe there are 2 thermostats on these cars, the main thermostat and the secondary cooling thermostat. Just FYI and sorry I don't know where the second one is.

If there is I have not found it

**psiaddict** · 12-03-2009 07:38 AM

I believe it's by the auxiliary water pump.

Check out this post in one of my old postings. Someone else at least confirms there is a secondary.

Not saying it has to be replaced; I don't even know when it would need it, but the dealer replaced all my cooling components to try and solve a problem I had. I just saw the parts list and thought it was weird this car has 2.

**sluggyjunx** · 01-13-2015 10:19 AM

OK guys, I just did the thermostat replacement in my 2005 B6 S4 Avant. What a bear. I searched and searched for DIYs on this and could find nothing more than a brief description of the process. The most challenging step is fitting the new thermostat into the old housing.

The difficulty lies in that you have to compress the “wings” of the thermostat down while twisting it into position. My fingers are still aching from trying to do this for hours until a friend made a suggestion that worked beautifully. Read on.

Parts:

Thermostat 0791211113F
http://www.ecstuning.com/ES284815/

Thermostat Housing Gasket 079121119
http://www.ecstuning.com/ES284820/

* OR if you like you can buy the entire housing with a thermostat pre-installed! Very nice but more expensive. Up to you. Note: you will still need a gasket!
Thermostat including Housing
http://www.ecstuning.com/ES284814/

Instructions

Jack front of car up and secure on jack stands
Remove front belly pan
Put a clean container underneath to catch coolant.
Remove coolant reservoir cap
Remove coolant drain plug from bottom of thermostat housing (hex bolt)

Allow all coolant to drain. This may take 10 min or so. Your patience will be rewarded.

Replace drain plug & washer
Get another small container to catch any additional drips as you work around the thermostat housing
Remove hose clamps for two coolant hoses connected to thermostat housing
Carefully remove hoses from thermostat housing. May have to use a pick/screwdriver to free them - they will be on there tight if they've never been off.
Using an inverted torx bit/star socket, remove four bolts from thermostat housing. Coolant will drip/pour out - have a container ready.
Remove thermostat housing from car.
Remove o-ring from water pump assembly.
Clean surfaces of thermostat housing and water pump assembly. I used a razor blade and towel to very VERY carefully scrape it. Be sure not to scratch or gouge the soft metal surface!
Install the new o-ring by first dipping it in clean coolant and then carefully installing it in the groove in the water pump housing
Now, take the housing to your bench with the new thermostat to work on it
To remove the old thermostat, you'll want to use a screwdriver to carefully walk the two "wings" of the thermostat out of the housing. The thermostat is installed in a way so that tremendous pressure is pushing up on the wings. You'll push down on one wing and move it about 1/8" of an inch, slowly walking it out of the housing. Be careful and wear gloves or use a towel. The thermostat can pop a bit and has some sharp edges.

Now for the trick to compress the new thermostat. I spent literally hours trying to figure out how to compress the new thermostat to get it into the housing. I tried boiling it to soften the spring, tried using my hands, tried using screwdrivers - all sorts of things to get it in. The problem I had was twofold. One, the spring is just too strong to push down on, seat, turn and position in the housing. It's a small space. Second, the "return spring", or the smaller spring that pushes against the main spring of the thermostat, gets in the way when you are trying to compress the wings of the thermostat. I tried to come up with contraptions to hold the wings down when I did, a few times, compress the thing. All of them failed.

The solution came from a friend. Zip ties. Yep.

Grab about 4 heavy duty zip ties. Thread the ties around the coils of the large spring in the thermostat and tighten. Do one at each quadrant of the spring. Pull the zip tie as tight as you can, and work your way around. Slowly. Eventually you will compress the spring quite a bit, which will allow you to press on the wings!

With the zip ties still in place, position the thermostat in the housing. Make sure of two things - one that the piston end of the thermostat is settled in the hole at the bottom of the housing and two that the small breather valve in the thermostat base is positioned at the "top" side of the thermostat housing. (ie. opposite the drain plug hole)
Once in position, carefully push down on the wings of the thermostat and turn it into position. You may need to use a screwdriver on one side to get good pressure.

Walk the wings into position in the housing, one side at a time, until it is in position.

Once it's set in position, cut the zip ties with a sharp knife.
Check the fitment and make sure it is seated properly and looks correct.

Reinstall the housing in the car the same way it came out, in reverse. I do not have torque specs for the housing bolts.
Don't forget to reconnect the hoses and clamps. Pause to check that everything is back in place.
Refill the coolant using a funnel and pouring it into the coolant reservoir. Burp the system as you go by gently but firmly squeezing the large coolant hose coming out of the front of the coolant reservoir.
It will take time. Keep an eye on the reservoir. Do not overfill. This can take about 10 min or so. Just keep at it. Once you have replaced about 85% of the coolant, check for leaks.
Start the car and let it warm up. As the system pulls coolant in, add it so that the level stays in between the MIN and MAX level on the coolant expansion tank.
Check for leaks.
You should be able to put nearly 100% of the coolant back in. If not, make sure to check after a day or so.
Run the car and let the thermostat click on to cycle coolant through.
Clear the code - using your scan tool, clear the codes on the car.

* You may notice that bag of ice in the background. That was there because in a fit of rage I threw the thermostat in the trash can, smashing my finger in the process. This is after about 5 hours of trying to get the thermostat in the old housing and failing. I still can't believe how great the zip tie trick worked. Simple & elegant. Hope it helps. :)

That should be it. Remember to double check for leaks. My car has the P2181 CEL code. I replaced the coolant temp sensor and now the thermostat and it still has not remedied the problem. The next thing to try is the secondary thermostat or the check valve. Also remember, I'm no expert. This install worked for me but someone may say "DON'T DO THAT!" - I will happily update & amend this DIY should I need to. Thanks for looking.

**BCsniper** · 01-13-2015 12:17 PM

want a hint? ........use a big socket to compress the thermostat

I tried pushing it down by hand and after a few seconds of nearly ripping my palm apart I went to the toolbox and grabbed something to compress it evenly. Worked like a charm and took me 5 seconds.

replacing just the thermostat and not the housing with it saves you ~$75 iirc and only takes a few seconds to do (if you use the right method)

**daad729** · 01-13-2015 12:19 PM

Awesome write up! - Just out of curiousity, would the zip tie trick work to help remove the old thermo? It could help relieve some of that pressure?

**jr1415us** · 01-13-2015 03:03 PM

Originally Posted by BCsniper

want a hint? ........use a big socket to compress the thermostat

I tried pushing it down by hand and after a few seconds of nearly ripping my palm apart I went to the toolbox and grabbed something to compress it evenly. Worked like a charm and took me 5 seconds.

replacing just the thermostat and not the housing with it saves you ~$75 iirc and only takes a few seconds to do (if you use the right method)

Or a piece of pipe.

**Gosser** · 01-13-2015 03:06 PM

I had the same codes as you. See the bottom of this page:
https://www.proj-build.com/build.php...chapter_id=624
It describes the issues with the thermostat housing and why they too need to be replaced. If you didnt do a water test, you might want to pull the housing out again...
Also goto the general information page, which further describes the check valve that some times gets stuck open, which you can visually verify from looking under the car. If it has, then it will rule that out as well.

**sluggyjunx** · 01-19-2015 06:13 PM

Thanks guys for the additional tips! Awesome info. I love the pipe idea. Yep, I need to look into the check valve issue, too.

Unfortunately I am probably not going to get to it b/c I'm going to be selling the S4 this week. :(

**sluggyjunx** · 01-19-2015 06:15 PM

Originally Posted by daad729

Awesome write up! - Just out of curiousity, would the zip tie trick work to help remove the old thermo? It could help relieve some of that pressure?

Probably. Also try the socket/pipe methods mentioned here as well. Or combine them all! :)

**m-ys4** · 02-12-2015 11:15 AM

to bring this thread back up, did you guys experience very long warm up times like around 25 minutes or so? and fluctuating temp readings?

**Gosser** · 02-12-2015 04:45 PM

Originally Posted by m-ys4

to bring this thread back up, did you guys experience very long warm up times like around 25 minutes or so? and fluctuating temp readings?

My car did the same thing, which was attributed to the scored thermostat housing. Check the link above to see what it looks like.

**m-ys4** · 02-12-2015 08:35 PM

Great link, how significant was the warmup after you completed this?

Sent from my iPad using Tapatalk

**m-ys4** · 02-13-2015 06:42 AM

the only difference is that I have not received any engine codes yet for long warm ups...

**Smokn337** · 02-13-2015 01:15 PM

I need to do this on my car. When coasting downhill, my temps drop to less than 45deg. Car never hits full warm unless a long uphill stretch. I only throw codes when temp reading is low and I floor it... I have bluetooth OBD reader in the car that I just clear the code with when it happens. Once my new clutch is in, this will be my next project.

**m-ys4** · 02-13-2015 01:34 PM

ive been doing some reading, in the spring im gonna do the thermostat and gasket, and the little 40$ valve that is attached to the lower rad hose ( I believe that's it) the check valve. this should solve the fluctuating issue I am having and super slow warm up

**DarrenOman** · 02-15-2015 08:06 AM

I've also read the secondary radiator inline thermostat can cause temp gauge fluctuation. I believe it's the pipe that goes from the top of the main rad to the top of the aux rad and its known as the non black hose. It fails open and doesnt let the car get upto it's design operating temp.

**Dolphin S4** · 02-15-2015 12:22 PM

Can anyone post a link to the secondary thermostat location and part number ? I'd like to do both. My car doesn't warm up quickly on colder days.

**Gosser** · 02-15-2015 03:02 PM

Originally Posted by Dolphin S4

Can anyone post a link to the secondary thermostat location and part number ? I'd like to do both. My car doesn't warm up quickly on colder days.

Aux thermostat:
http://www.ecstuning.com/Audi-B6_S4--V8/ES436132/
Pricy, but dont know if you can purchase it without the hoses.

See the part diagram here:
https://www.proj-build.com/build.php...chapter_id=499
Half way down the page, part number 12.