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  1. #1
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    replaced thermostat - coolant now not circulating.

    Hi guys.

    I replaced the thermostat on my 1.8t a4 today.

    Now im not getting any hot air through the blowers and the coolant doesn't seem to be circulating.

    I have drained and bled the system 3 times as per the guides on here ie sliding the heater intake back to the bleed hole until water comes out etc. but still the same issue.

    I have removed the new thermostat again with the housing and when i put it in boiling hot water it doesn't seem to be letting water through the inlet, it just sits in the tube.

    Would a faulty thermostat cause me not to get coolant circulating to the heater.

    When i release the coolant resevoir cap it spews a load off coolant out as if its boiling up.

    Im worried that it may be the water pump.

    I intend to refit the old one and test it again but wondered if anyone had any thoughts?

    Thanks folks,

    Dan.

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  3. #2
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    Hi dan what was the reason for replacing the stat? Water pumps are pretty common,they have the dreaded plastic impeller which can break off and cause overheating. If your heater doesn't work i suspect you may have an airlock or possibly a blockage, regards to the thermostat , ive tested them myself and i often carn't get them to open up. I find if you heat them with a mini blow torch they will open up.

  4. #3
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    Hi Tony.

    It was taking ages to get upto 90 on the temp gauge and as soon as i set off it would drop down to about 70 or even lower sometimes and then only get back upto 90 if i stood still for a while.

    I have tested the old thermostat and it is definately stuck slightly open so it is faulty.

    I had the water pump done a few weeks ago after it failed.

  5. #4
    bez101's Avatar
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    the stat should open in boiling water
    if it doesnt then its prob faulty
    iv fitted a new oem stat b4 and it was faulty

  6. #5
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    Would a stuck shut thermostat cause the problem of the water not circulating to the heater inlet?

  7. #6
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    yes if its stuck closed it wont let the hot water through

  8. #7
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    The heater is the bypass, its in the loop all the time, even when the stat is closed.

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
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  9. #8
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    so it wouldnt make a difference if the stat was closed.

    it sounding like the water pump to me.......just hope the garage i had it done at won't say ive done it whilst changing the stat!

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    is there a way i can test for the water pump? ie take a pipe off when its cold and see if water flows when i start it up?

    Should ther be water flowing through the heater inlet pipe as soon as it starts up?
    Last edited by casiodan; 31st December 2010 at 09:32.

  11. #10
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    Quote Originally Posted by casiodan View Post

    Should ther be water flowing through the heater inlet pipe as soon as it starts up?
    Yes as already said the heater is on its own loop and has nothing todo with the stat so water should flow .

  12. #11
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    Quote Originally Posted by quattro tony View Post
    regards to the thermostat , ive tested them myself and i often carn't get them to open up. I find if you heat them with a mini blow torch they will open up.
    Stats open around 87-89 degrees if they dont open in a boiling kettle of water there buggered
    as for heating them with a blow lamp at what 400degrees if they were not buggered already they would be then .

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    ok. old thermostat back in and now blowing warm air!

    Why would a themostat cause that issue if the heater bypasses the thermostat?

    Is it possible i have bled it properly this time but not the first time? I guess with a thermostat stuck open (ie the old one which is back in now) there is more opportunity for the coolant to flow and release air?

  14. #13
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    It does sound like a air lock to me, Possible you may have a faulty stat. Have you checked the opening temp of it that it is exactly the same as the old one?, just to make sure its exactly the same and correct one.As regards to heating them i only do it if im really struggling with a thermostat problem, I am aware its not the recommended way of doing it

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    another update.

    Took it for a run everything ok, left it ticking over for a bit and it started to overheat. Temp on vag com was 97 and then i switched it off and could hear it bubbling a little bit.

    Someone who was passing just said cylinder head!!!! please someone tell me thats not the case!!!

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    just looked at the housing on the new one and it says 100c, i take it this is referring to the temperature?

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    and another odd thing i noticed? if i slide the pipe off the heater inlet the coolant is coming back out of the bulkhead?? Shouldnt it be coming from the hose?

  18. #17
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    Perhaps you slid off the return pipe rather than the feed?

    Its entirely normal for the car to reach 97c or higher when left idling, as theres little airflow to cool it down. The viscous fan will "hook up" around 100c to help pull it back down again. Things shouldnt start boiling until well over 100c, unless you've got the expansion tank open. The system is designed to run pressurised, so if you have the tank open (or its cap is faulty), then its going to boil over.

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    i slid off the top pipe with the bleed hole in it?

    Im gonna try it one more time double checking everything is on tightly. and keep an eye on the temperature.

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    right, I figured out what caused the overheating with the old thermostat back in.

    I havent got one of the clips back properly on one of the pipes and as soon as the thermostat opened fully the pressure caused the coolant to squirt out and caused alot of steam, im gonna go enjoy myself tonight and then try again with the new thermostat on sunday.

    I say it every time but this is why i should leave it to the experts..........if ive got toothache i go to the dentist, what possesses me to try and fix my own car ill never know!

    Thanks for all your help guys, its much appreciated.

    Happy new year everyone.

    Dan

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    Just a quickie.

    The thermostat on mine is an electronic thermostat right?

    Can someone explain how the electronic thermostat works? does this mean its not possible to test them using the boiling kettle trick?

  22. #21
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    Quote Originally Posted by casiodan View Post
    Just a quickie.

    The thermostat on mine is an electronic thermostat right?

    Can someone explain how the electronic thermostat works? does this mean its not possible to test them using the boiling kettle trick?
    Electronic Thermostat ??

  23. #22
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    Read it in this guide

    AudiWorld Tech Articles

    It says :-

    Note that I found it helpful to remove the single accessory belt by taking off the alternator while holding the tensioner (things are real tight without doing so). Also you need to remove this to access the electronic thermostat which is different on the B6 compared to the mechanical one of the B5. Make sure you have replacement o-rings for the t-stat as well as metal pipe that connects to it.

  24. #23
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    That links dead
    also i have never seen or changed an electronic thermostat on anything including a B6
    im genuinely intrested .
    Last edited by paul20v; 1st January 2011 at 20:41.

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    Well it seems like the new thermostat is either wrong or dead.

    I got a mechanic to help me reinstall the new one and properly bleed the system

    It got up to temp and then started to boil up. When we felt the bottom hose it was flat cold. So we put the old one back (again) and once we got it up to temperature which took a while due to the slightly open old stat things went fine. Bled up really easily and as soon as vagcom read 96 the stat opened the fan kicked in and the temp dropped back down to 90 and just kept cycling 90 upto 96 and back down with the fans. Obviously with the dodgy original stat when I start moving the temp drops down as soon as I get a bit of air flowing through the radiator which is the problem I was fixing originally.

    So it's either a faulty stat or the wrong one. I got it from gsf and they couldn't find my reg number. This is a regular occurance because the car was initially registered in germany. Can anyone tell me how else I could confirm the correct thermostat with gsf.

    The guy did say all the possible options used the same thermostat?

  26. #25
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    yup the 1.8T uses a electronic stat!!!

    sounds duff to me get a new one for Audi or try this one Audi - Euro Car Parts UK

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    The new one I got looks right and fits right. Is the multiplug something to do with it been electronic or is that just a sensor for something?

    Would a non electronic stat have the multiplug connector on the housing?

    Are there other thermostats that would come in the same housing?

    I don't think gsf will refund me, just exchange it so I want to make sure I know if it's faulty or wrong if possible.
    The guy asked me for my engine code, I didn't know it, I stupidly said b6 but now I know that's not the engine code. Does anyone know what my engine code is? It's the 163 version if that makes a difference

    Cheers

  28. #27
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    its prob a AVJ
    but look on your v5 or service book front page big white sticker

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    it is an avj, i found it stamped on the engine.

    Is there a way to test the new thermostat? and is it possible that a new one is faulty?

    Im just a little worried that because my old thermostat is slightly opened it might be masking another fault such as the water pump.
    Last edited by casiodan; 2nd January 2011 at 13:22.

  30. #29
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    i am getting good heat to the blowers. would this rule out the pump?

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    Right final theory before i take it somewhere.

    I have got the new thermostat to open in boiling water but its not opening in the car before i start getting bubbling in the system. I know that its not opening because the bottom hose is staying cold.

    Would a failing water pump cause there not to be enough flow to the thermostat for it to open? I am thinking the old, stuck slightly open, thermostat is letting some water through and allowing hot water to pass the thermostat even if the pump is only partially working (maybe slipping on the spindle slightly) enough to make it open but the new one is stopping any flow and with a defective water pump not enough fully hot water is getting into the housing to open the thermostat.

    I am hearing a bit of a noise when i rev the engine that i haven't heard before, sort of a tappety noise but its not coming from the tappets? Maybe its the paranoia that sets in when these things happen.

    My uneducated theory is the water pump failing anyone agree?



    EDIT- I just retested the stat and the water was boiling for quite a while before it opened? Maybe it is opening too late?
    There is absolutely no flow until it has been in boiling water for about 2 minutes and then it opens completely. It should open slighly before boiling point right?

    Damn it!!!! i cant make my mind up!!! Im gonna exchange the stat and try again but im not convinced?
    Last edited by casiodan; 3rd January 2011 at 15:49.

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    my worst fear may actually be right!

    Ive just been out in it and noticed steam from the exhaust. When i smelt it it smelt sweet i think. Ive got a feeling the head gasket is gone/going and the excess pressure caused the temp sensor housing to blow which is when the thermostat started sticking open.

    Im going to get another replacement thermostat tomorrow anyway but i think im gonna get the same problems.

    Whats do they call the test you have done to check the head gasket? ive seen it where they have liquid in a tube that turns yellow?

  33. #32
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    Quote Originally Posted by casiodan View Post

    Whats do they call the test you have done to check the head gasket? ive seen it where they have liquid in a tube that turns yellow?
    We call it a sniff test where i work we measure for (HCs) Hydro carbons in the water but we use the 4 gas exhaust analyzer
    but there is a leak detection kit available i just dont know where sorry.

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    thanks paul. is that the analyser you use for doing the MOT emissions testing?

    Do you think my theory is possible. I do only do short journeys and obviously the open themostat means the engine hasn't been getting upto temp so condensation is possible but its the smell that is making me think head gasket/head.

    Ive got that sick feeling again!

  35. #34
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    Quote Originally Posted by casiodan View Post
    thanks paul. is that the analyser you use for doing the MOT emissions testing?
    Yes mate it is
    most of them will give live readings and if you put the probe in the bottle (not in the water) you should have no HC reading at all
    but if the gaskets leaking cylinder pressure into the water it will give HC readings they are accurate as there measured in PPM Parts Per Million .

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    ill get it checked tomorrow.

    Im confused as to why its not overheating with the original thermostat in? when it eventually gets up to temperature the stat opens fully and the temp drops back down?

  37. #36
    scott b's Avatar
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    as you say you do short journeys, as the stat is slightly open it will be letting all the water in the system run through the engine, where as if it was working correctly it would stay closed till the engine was warm then it would let the rest of the water in the system run through the engine if that makes sense

  38. #37
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    Hi Scott,

    I know what your saying with the thermostat, it is letting the coolant flow constantly, this is verified by the length of time it takes to warm up and the fact that the bottom hose heats up from cold at the same time as the top hose. What is confusing me is when it does get up to about 96 the fan kicks as normal and cools it all down however when the new stat was in it started bubbling before the stat opened, which coupled with the steam and the problem that started all this off, the split temp sensor housing, it sounds like the system is over pressuring........that to me could be the head gasket.

    Im going to get another thermostat just to rule that out and see what happens but ive nearly convinced myself that the head gasket is leaking.

  39. #38
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    I had this exact problem.

    Car was running cool, so i fitted a new (but cheap) stat.

    New stat wouldnt open, and temp went silly high and bottom hose stayed stone cold.

    Refitted old stat and it went back to running cool again.

    Threw the new stat away, and baught a decent branded one (Topran iirc) and fitted that, which fixed it.

    You will get steam from the exhaust on a cold engine, its nothing more than condensation.

    Get a new stat in there, and DRIVE the car to get it up to temperature, dont just leave it idling on the driveway.

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
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  40. #39
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    It's not totally uncommon to get a duff stat!! Yeh there is a electronic stat, my 1.8t (bex) has one, they have a couple of plugs and it's a big plastic hobby!! I didn't remove the alternator just a stay from the manifold too block!! Mine was open and overbooking, now sits at 90 all the time!!

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    Cheers lads,

    I hope you are right Aragorn, if its more serious than the stat im afraid its the end of the road for the car with me. I just cant afford to be replacing the head.

    I feel a SORN coming on.

    fingers crossed on the stat.

 

 
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