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Cold running issues, Thermostat or temp sensor?

Discussion in 'A3/S3 Forum (8L Chassis)' started by Prawn, Oct 19, 2007.

  1. Prawn
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    Prawn My other car is a MINI!!!!

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    [Oct 19, 2007]
    Hi Guys, I’ve been pondering this for a while, and decided now it doesn’t seem quite right, so thought id ask advice.

    My car doesn’t get up to temperature on the motorway.

    Around town, and in traffic, the car gets up to 90ish, and stays there (true 90 displayed on air con not dash reading)

    It tends to hover between 83 and 95 in traffic and usually just under 85 around town.

    I drive 30 miles up the A3 to work everyday, and on the A3, doing around 60ish most of the way, it very rarely gets above 70 at all!

    Yesterday, I drove the whole way home at 80 and it was still only reading 63 degrees after 32 miles!

    I know that cars will run colder with good airflow across the rad, but it never seems to get up to a decent temp at all on the dual carriage way.

    Is this likely to just be the sender? Or is it more likely to be the thermostat?

    Where is the stat on the 1.8T engine? How easily is it replaced?

    I know the temp sender is dead easy, but I’ve not heard much about the stat.

    Any advice welcome!

    Thanks guys.
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  3. Mike H
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    Mike H Member

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    [Oct 19, 2007]
    I thought this was normal? When I'm on m/way... the temp gauge drops slightly from 90 all the time. Didn't think anything of it to be fair, I just thought it was with the cool airflow?

    Hope so anyhow!!
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  4. jonS3
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    jonS3 Member

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    [Oct 19, 2007]
    mine did this, and a new thermostat later it never strays away from centre.

    you can do the old climate control 49 trick, to give you true readings....
    #3
  5. S3-ROB
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    S3-ROB RD350YPVS - Loves 2 stroke oil

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    [Oct 19, 2007]
    As above, sounds like the thermostat, mine stays at 90 at all times, traffic or on a long run :icon_thumright:
    #4
  6. HTC
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    HTC Active Member

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    [Oct 19, 2007]
    100% thermostat. Mine and a mates at work had exactly the same issue.

    After the change, it should sit at bang on 90 all the time.
    #5
  7. Tooks
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    Tooks Active Member

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    [Oct 19, 2007]
    Another vote for a faulty thermostat here.

    The gauge should be reading 90c all the time once warmed up.
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  8. Prawn
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    Prawn My other car is a MINI!!!!

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    [Oct 22, 2007]
    righty then, new stat is is guys!

    I'm not taking my readings from the dash gauge by the way, I only ever read the 'climate 49' reading.

    How easy is it to change the stat? where is it on the 1.8T?

    I just drove 36 miles up the A3 and it never reached 70 degrees!

    also didnt pass 75 the whole way to Paris and back this weekend, and strangely, the car seemed less economical than usual....

    I'll try and get the stat changed in the next few weeks.

    Is it true that the ECU limits boost when the engine is cold? at what temperature does the ECU deem it acceptable to run full boost? at 70degrees water temp will I have restricted boost?
    #7
  9. luis.filipe
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    luis.filipe Member

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    [Oct 22, 2007]
    Hi, add the same issue on my 1.8T.

    First replaced the temperature sender, for a green one and it behaves like you described!

    The solution was to buy a new stat, and the problem was fixed.

    About this issue I also read a lot about the boost, and something related with higher fuel consumption :sadlike:. Since I drove the car a lot of time with this what I noticed is that my spark plugs are a bit black not to much.

    According to Haynnes this might be a very rich misture, and I think that this might be related with the engine never getting to the normal operating temperature.

    I'm curiousos about the boost issue!

    Regards
    #8
  10. Mike H
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    Mike H Member

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    [Oct 22, 2007]
    Thanks!! looks like I'll be buying a new stat too!
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  11. HTC
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    HTC Active Member

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    [Oct 23, 2007]
    The thermostat is on the block behind the alternator. Its a fiddle, but fairly straight forward. Plastic housing holding it is secured by two 10mm bolts. Can't be sure, but they may be the type with both a hex head and allen socket, so you should have a choice to use a spanner or an allen key/socket.
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  12. Prawn
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    Prawn My other car is a MINI!!!!

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    [Oct 23, 2007]
    oh right, so its not behind the water pump or anything nasty like that then?

    I guess nothing else has to come out to replace the stat? does the alternator need moving?

    If its an easy enough job, I'll get one and do it this saturday :)

    How long do you reckon it should take roughly?
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  13. comdw
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    comdw Member VCDS Map User

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    [Oct 24, 2007]
    Well this is handy as I was about to post the same question. My car has been running cold for a while (never above 77 on the climate no. 49 readout if the car is moving). It only gets up to 90 when i leave it sitting at a standstill.

    No temp sensor faults on the VAG-COM, so was going to change thermostat rather than temp sensor. Has anyone done this job yet and know how difficult or easy it is? Do you lose coolant when doing this?
    #12
  14. luis.filipe
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    luis.filipe Member

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    [Oct 24, 2007]
    I haven't performed this job!
    I asked my mechanic to do it for me.
    At the same time I bought 3 liters o G12 plus and asked him to put it.
    The coolant taht was being used wasn't good :(
    I can't tell you if we are going to loose much coolant or not.
    I replaced mine at the same time.
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  15. HTC
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    HTC Active Member

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    [Oct 24, 2007]
    Official guide mentions removing the alt, but I've done a few, and its fine with the alt in situ. You just remove the engine cover around the dip stick and then the metal dipstick tube holder.

    Yes you will lose a whole load of coolant. You drain the rad from the handy tap on the bottom, then remove the rubber pipe on the right hand side of the oil cooler to relase the coolant from the block.
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  16. HTC
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    HTC Active Member

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    [Oct 24, 2007]
    Tiny pic of a 1.8T block.

    Thermostat hole is top left.

    [​IMG]
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  17. comdw
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    comdw Member VCDS Map User

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    [Oct 25, 2007]
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  18. HTC
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    HTC Active Member

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  19. comdw
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    comdw Member VCDS Map User

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    [Oct 28, 2007]
    Replaced my thermostat today. Must admit it was a bit of an ordeal for me getting to those two awkward bolts - anyone else attempting this, you'll need as short a 10mm socket and flex joint as possible to get purchase on the bolts. Mine kept slipping off because I couldn't get it right behind the alternator properly, but got there in the end.

    Thought I lost quite a bit of coolant, but didn't need to top up too much even after running the engine to full temp. So now I'm worried about having air in the system. Also noted the radiator fans never came on (temp reading was up to 94) and coolant pump didn't run after switching off. Not sure if this is a problem yet, won't be driving it till tomorrow.
    #18
  20. abdus
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    abdus Top Gear VCDS Map User

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    [Oct 28, 2007]
    to rmove air from the system, just remove the coolant bottle cap and let the car run for 2-3 mins...should remove the air trapped (if any)

    did you disconnect (/unintentionally) any other electrics? might be why fans not working
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  21. comdw
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    comdw Member VCDS Map User

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    [Oct 30, 2007]
    The fans do work as they always run when the aircon is on (assume this is normal). I might not have let it get hot enough to switch the fans on anyway yet, will need a longer journey followed by leaving the car sat idling for a while.

    Less sure about the electric coolant pump as I haven't heard it run yet. Is this supposed to *always* run after the engine is switched off or is it only above certain temps? Does it have its own fuse I could check?
    #20

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