2002 a4 18t bad thermostat?

[Frunzman]

OK i know there are multiple threads regarding this issue, but i want some input on my specific issues. been searching the forums through and through. i recently purchased an 02 a4 1.8t. i was told by the dealer the timing belt was recently done. I have very little heat (very little at idle) and slightly better heat as rpms raise. i recently bled my system via heater core hose, and the bleeder valve near manifold. i did get air out of both areas and topped off coolant as needed. heat in cabin has gotten slightly better but i feel not nearly as good as it should be. when bleeding, i wait a while with the top line off of the heater core, no coolant comes out until it seems the thermostat opens, then shoots out like a super soaker. i am noticing during driving, my temp gauge reaches the middle (takes about 15 minutes of driving), and sticks there, until i noticed it does drop below the half way mark upon coasting (downhill) but not very often. then driving goes back up to half but NEVER above half. only code im getting right now is for an 02 sensor. as far as i can tell it seems that my thermostat may be stuck open, being as timing belt was done less than 500 miles ago wouldnt they have done the thermostat as well?? purchased car as-is. will be replaing thermostat myself if i deduce thats what it is, but hear it is no fun to replace. any input is greatly appreciated.

[Matt Devo]

thermostat isn't done as part of the TB service on these cars, and it definitely sounds like yours is stuck open. Replacing it isn't that bad, I did a DIY a few years back; search for that

[jursch2211]

I have a used one available that I would sell for cheap if you want it. It has maybe 15K miles on it. I know a used one might sound bad but at least if it is the t-stat then you can fix your problem for a small cost that could last for a while. Just throwing it out there.

[walky_talky20]

Usually the t-stat is not done as part of t-belt job, but on the B6 I always look at them really closely. The top of the housing likes to crack and break sometimes. It is not uncommon that a B6 1.8T will need a thermostat before the 2nd t-belt job. But they are pricey, so most just wait until they have a problem.

I will suggest that if you go in for the t-stat, you should also replace the "J-Plug". And make sure you get the elusive o-ring for the hard pipe, too. ECS has some nice kits so you have everything you need:

ECS kit w/Aftermarket T-stat

ECS kit w/Genuine OEM T-stat

I'd recommend either OEM or Aftermarket "BEHR" brand. I'd probably skip on the "MTC" aftermarket part, given the choice.

[Frunzman]

okkkk, so today i bit the bullet and replaced the thermostat. car heats up MUCH faster, and is rock solid temperature through all types of driving. i bled the system via the bleeder on the manifold and the top heater core hose. i took it for a test drive, stopped after about 5 minutes to top off with coolant. drove it back home and checked again, as soon as i opened the expansion tank this time, it started shooting coolant out of the bottom pressure release or whatever drain it is, and my whole engine sounded like it was boiling. any advice?

[Furly]

You're not supposed to open the coolant reservoir after driving the car. You gotta wait a good amount of time for the system to cool down.

[Frunzman]

im thinking about doing a heater core flush tomorrow, should have done it today while i had the coolant out but i had high hopes for the thermostat replacement. ill let you know how it goes.... still thinking its more likely air in the system, but ive bled and bled with no vast change...

[diagnosticator]

Never remove the expansion tank cap before the engine has cooled down. Releasing the pressure will provoke boiling in the engine cooling passages if the coolant is not flowing.

Do not attempt to bleed the system with the cooling system hot, or with the engine running. Bleeding the system must only be done with the cooling system at ambient temp, and the engine turned OFF.

If the cooling system continues to have air and bleeding does not remove all the air, then there is a leak somewhere, allowing air into the system and coolant to leak out.

Refilling the cooling system slowly, and waiting at least 45 minutes for the system to fill from the expansion tank, topping up the tank level as needed, will usually prevent air being trapped in the system. If the process is rushed, the system will not be completely filled from gravity feed, and air will be trapped in the system. Enough time to fill the system from gravity feed requires at least 45 minutes or more. If done to quickly, the system will seem to be filled, but will not have had enough time to fill all the way.

[Frunzman]

diagnosticator, would you recommend bleeding the system through the heater core output at ambient temp with the engine turned off? seems the only way i can get either bleeder to produce anything is if i have someone revving the engine, then i get intermittent bubbles and coolant. otherwise i get nothing? im assuming you mean to run car to ambient temp, shut off and use bleeder but im uncertain how air bubbles would come out this way? when filling the coolant, i left the car off until filled in the expansion tank and did not appear to be dropping in level anymore. i then started the car and let run at idle filling the expansion tank as it dropped. once it seemed to not drop anymore i took a short drive, checked filled and repeat. as said before heat is better but still what i imagine it should be.

[Frunzman]

another stupid question i know, upon inspecting the expansion tank i could see a small drip of coolant at the bottom, upon further inspection i noticed there is no o ring, not inside the cap not inside the tank itself? i feel maybe there should be one there but can find no answer online, anyone know if im right?

update: there is a small oring on the inside of the cap on the black center. no other o rings needed i guess?

[redline380]

Do not attempt to bleed the system with the cooling system hot, or with the engine running. Bleeding the system must only be done with the cooling system at ambient temp, and the engine turned OFF.

Well how in the Sam Hill am I supposed to bleed coolant without the engine running? Put my lips on heater hose and suck all the air out of it?

I have honestly never heard of anyone saying this before. Guess I have been doing it wrong all these years?

[Luxus Panzer]

another stupid question i know, upon inspecting the expansion tank i could see a small drip of coolant at the bottom, upon further inspection i noticed there is no o ring, not inside the cap not inside the tank itself? i feel maybe there should be one there but can find no answer online, anyone know if im right?

update: there is a small oring on the inside of the cap on the black center. no other o rings needed i guess?

Blow (pressure) or elevate the expansion tank and let gravity do the work over time.