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  1. #1
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    Coolant temperature uneven. Please help

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    Hi
    I have a 2011 A4 and the coolant temperature gauge is reading uneven numbers. After about 30 min of driving, the needle stays like this. Sometimes it reaches the middle but then drop down after a few min


    However the weirdest part is when I do down hill. The temperature dips down to this


    and then rises to the the temperature in the first pic after 20 sec.

    I scanned for any codes and nothing came up. Any suggestion?

    The car blows hot air like it normally does. It's not cold here in sydney. around 22-28 C
    Last edited by OrkSina; 02-11-2019 at 06:02 AM.

  2. #2
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    Do you have a VCDS or anything that can display, or even better log, engine parameters?

    The best thing would be to try to "catch it int the act", monitoring the coolant temperature while the problem is occurring. If the temperature is actually varying you know the problem is actually with the coolant temperature, or maybe the sensor. If the temperature is not varying but the gauge is moving, the problem is with the gauge.
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  3. #3
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    Quote Originally Posted by ELaw View Post
    Do you have a VCDS or anything that can display, or even better log, engine parameters?

    The best thing would be to try to "catch it int the act", monitoring the coolant temperature while the problem is occurring. If the temperature is actually varying you know the problem is actually with the coolant temperature, or maybe the sensor. If the temperature is not varying but the gauge is moving, the problem is with the gauge.
    I have a ODIS cable that I used to get rid of my component protection in my previous Audi. But I'm not exactly sure how to log the engine parameters. Any guides?
    How can I monitor the coolant temperature? When I accelerate fast, sometime the needle will go way below like on pic 2.

  4. #4
    Established Member Four Rings Novarider's Avatar
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    Mine does this as well if I coast down hill for a while like coming down a mountain. I thought it was normal. It never does it while driving flat or climbing the mountain.
    2011 A4 Avant Prestige S-Line

  5. #5
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    Quote Originally Posted by OrkSina View Post
    I have a ODIS cable that I used to get rid of my component protection in my previous Audi. But I'm not exactly sure how to log the engine parameters. Any guides?
    How can I monitor the coolant temperature? When I accelerate fast, sometime the needle will go way below like on pic 2.
    I had the same "issue" and brought it up to my dealer. Spoke with the master tech there who also owns a b8.5. He told me this is normal in cold weather, the car prioritizes cabin heating over engine temperature. Kinda why right now in -20C weather I can start the car up in my driveway and let it run half an hour if I like, the temp will be all the way down but the cabin will be nice and toasty.

    Perhaps this also applies to a lesser extent in warmer weather?

  6. #6
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    Quote Originally Posted by snaky69 View Post
    I had the same "issue" and brought it up to my dealer. Spoke with the master tech there who also owns a b8.5. He told me this is normal in cold weather, the car prioritizes cabin heating over engine temperature. Kinda why right now in -20C weather I can start the car up in my driveway and let it run half an hour if I like, the temp will be all the way down but the cabin will be nice and toasty.

    Perhaps this also applies to a lesser extent in warmer weather?
    But the temperature over is currently 22-28*C. Shouldn't drop that significantly right? Tomorrow its going to be 37 I think. I'll see what happens tomorrow and post here

  7. #7
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    Quote Originally Posted by OrkSina View Post
    But the temperature over is currently 22-28*C. Shouldn't drop that significantly right?
    Mine doesn’t at those temps. Thermostat stuck open?

  8. #8
    Veteran Member Four Rings kaz02a4's Avatar
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    I had this happen on my B7. It was the thermostat sticking open. Changed that, and no issues.
    My B8, for what it's worth, has never had this happen.
    RIP B7: Stg. 1 UM, RS4 rear sway, Apikol snub mount, trip computer retrofit, OEM bi-xenons retrofit, RS4 seats retrofit, B7 S4 Ti wheels, BSH CC, 034 SD mounts, restitched steering wheel by my own hand

    Hello B8: P+ Quattro, 6 Speed, Sport. Stg. 1 APR, CR-15, S5 brakes, Fly Designs steering wheel, Euro Impulse shift knob, and the beginnings of a track day build...

  9. #9
    Senior Member Four Rings Theiceman's Avatar
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    Likely thermostat. But to be honest it doesn’t look serious.
    Is this anew behaviour ? This car is smart. If something is out if parameter range, this car will tell you



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  10. #10
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    Stuck open thermostat. Mine did what yours is showing for a while. Then it was only warming around 1/4, MIL came on. Replaced water polo and thermostat. All good.

    Sent from my Pixel using Tapatalk

  11. #11
    Veteran Member Four Rings MacFady's Avatar
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    I would say thermostat on its way out. How is the heat coming from the vents? I DD my car in temps ranging from +32C to -40C throughout the year, in the first 5 minutes of driving in very cold weather the coolant temp gauge will tend to start to dip if I'm sitting at traffic lights or something (no heat/fan on), but once the car reaches temp on the gauge I don't experience this, it stays put. Unless the fan is off and car comes up to temp then fan/heat is turned on (I generally leave heat/fan off until coolant gauge at temp), in that case it will dip down to the first mark on the gauge generally before climbing back up to the middle in 10-15 seconds.

  12. #12
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    So it sounds like, its the thermostat that's going bad. Is it expensive to fix? Is it possible to DIY?

  13. #13
    Veteran Member Four Rings kaz02a4's Avatar
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    Quote Originally Posted by OrkSina View Post
    So it sounds like, its the thermostat that's going bad. Is it expensive to fix? Is it possible to DIY?
    It's not too bad to do for a DIY. It is integrated into the water pump, which is under the intake manifold. If you haven't done a carbon clean before, now is your chance. There are a couple of good DIYs kicking around for them both.
    RIP B7: Stg. 1 UM, RS4 rear sway, Apikol snub mount, trip computer retrofit, OEM bi-xenons retrofit, RS4 seats retrofit, B7 S4 Ti wheels, BSH CC, 034 SD mounts, restitched steering wheel by my own hand

    Hello B8: P+ Quattro, 6 Speed, Sport. Stg. 1 APR, CR-15, S5 brakes, Fly Designs steering wheel, Euro Impulse shift knob, and the beginnings of a track day build...

  14. #14
    Senior Member Four Rings Theiceman's Avatar
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    anything Is DIY .. it all depends on your skill level, the tools you have and your level o commitment.
    The stat is inside the water pump assembly. look for a water pump DIY and this will give you a clue.
    2014 A4 2.0TQ Technik
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  15. #15
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    Should I go ahead and change the water pump as well?

  16. #16
    Senior Member Four Rings Theiceman's Avatar
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    given your climate where you are I would.. but it might depend on your milage and comfort level. changing a stat is VERY easy .. once you get access its a couple of bolts on the housing , replace , top up fluid.

    water pump is more involved. there is a you tube video for it by edge motors I belive. you can review that and make the call.
    2014 A4 2.0TQ Technik
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  17. #17
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    Quote Originally Posted by Theiceman View Post
    given your climate where you are I would.. but it might depend on your milage and comfort level. changing a stat is VERY easy .. once you get access its a couple of bolts on the housing , replace , top up fluid.

    water pump is more involved. there is a you tube video for it by edge motors I belive. you can review that and make the call.
    Over here in sydney, it gets around 45° C (Max) and the coldest is around 4° C. I asked a mechanic about it and they would charge me AUD $360 (USD 255) without parts. That's for the whole water pump assembly and the thermostat. If its easier to do just the thermostat by myself, I will probably do it. The car is only at 93,000 km

  18. #18
    Veteran Member Four Rings kaz02a4's Avatar
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    Quote Originally Posted by Theiceman View Post
    given your climate where you are I would.. but it might depend on your milage and comfort level. changing a stat is VERY easy .. once you get access its a couple of bolts on the housing , replace , top up fluid.

    water pump is more involved. there is a you tube video for it by edge motors I belive. you can review that and make the call.
    https://www.audizine.com/forum/showt...mp-Replacement

    The thermostat is integrated into the water pump housing.
    RIP B7: Stg. 1 UM, RS4 rear sway, Apikol snub mount, trip computer retrofit, OEM bi-xenons retrofit, RS4 seats retrofit, B7 S4 Ti wheels, BSH CC, 034 SD mounts, restitched steering wheel by my own hand

    Hello B8: P+ Quattro, 6 Speed, Sport. Stg. 1 APR, CR-15, S5 brakes, Fly Designs steering wheel, Euro Impulse shift knob, and the beginnings of a track day build...

  19. #19
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    Quote Originally Posted by kaz02a4 View Post
    https://www.audizine.com/forum/showt...mp-Replacement

    The thermostat is integrated into the water pump housing.
    NOOOOooooooo!!!

    https://www.ebay.com.au/itm/for-Audi...6/282630563074

    Is this all I need? Or do i need anything else?

    Btw Appreciate all the replies. Thanks a lot

  20. #20
    Senior Member Four Rings Theiceman's Avatar
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    to me 255 labour to replace it I would jump at... but yeah its only 93K km . I took my original off after 220K km and it was perfectly fine. just the oring was leaking for the temp sensor.
    2014 A4 2.0TQ Technik
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  21. #21
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    Quote Originally Posted by Theiceman View Post
    to me 255 labour to replace it I would jump at... but yeah its only 93K km . I took my original off after 220K km and it was perfectly fine. just the oring was leaking for the temp sensor.
    Can't just change the thermostat? Need to change the whole thing?

  22. #22
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    Quote Originally Posted by OrkSina View Post
    Can't just change the thermostat? Need to change the whole thing?
    Depending on the milage, it's best to do both since the water pumps are known to fail.

    I think I paid 700 parts and labor for a new water pump/thermostat, new coolant and all.

    I'd just do it and not have to worry about it for a long time.

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  23. #23
    Senior Member Four Rings Theiceman's Avatar
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    Quote Originally Posted by kaz02a4 View Post
    https://www.audizine.com/forum/showt...mp-Replacement

    The thermostat is integrated into the water pump housing.
    yes and no.....

    yes it is integrated.. but it is independently changeable with two bolts on the water pump.
    2014 A4 2.0TQ Technik
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  24. #24
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    Quote Originally Posted by OrkSina View Post
    Can't just change the thermostat? Need to change the whole thing?
    You can replace the thermostat separately. But you'll need to determine which part number you require. Look at https://nemigaparts.com/cat_spares/e...4q/636/121030/
    Part 9 is the thermostat alone, but notice there are three different part numbers depending on which pump part number you have. Your dealership should be able to tell you which one you need based on your VIN.
    You'll also need a replacement o-ring, part 11. Torque spec for the bolts, part 12, that hold on the cover, part 10, is 9 Nm.

    But it seems the replacement procedure is "drain coolant, remove pump, ...". Not sure if there's access to remove the thermostat housing with the pump installed.
    2009 A4 Avant 2.0T quattro Prestige, 182k miles

  25. #25
    Established Member Four Rings Novarider's Avatar
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    Still think it's normal since it ONLY happens when coasting down a big hill. It never happens when driving flat or going up hill no matter the temp or engine load.

    If it were a thermostat issue it wouldn't be so consistent.
    2011 A4 Avant Prestige S-Line

  26. #26
    Veteran Member Four Rings jfo's Avatar
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    Quote Originally Posted by Novarider View Post
    Still think it's normal since it ONLY happens when coasting down a big hill. It never happens when driving flat or going up hill no matter the temp or engine load.

    If it were a thermostat issue it wouldn't be so consistent.
    It may not be a problem, but I wouldn't say it's normal. I drive up and down mountain roads daily and have never experienced this or heard of anyone else seeing the temps change when coasting down a hill.
    2011 A4 Avant quattro tiptronic/ Eurocode Sway Bars, End Links, Alu Kreuz/ 034 Catch Can/ Various VagCom

  27. #27
    Senior Member Four Rings Theiceman's Avatar
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    Quote Originally Posted by jfo View Post
    It may not be a problem, but I wouldn't say it's normal. I drive up and down mountain roads daily and have never experienced this or heard of anyone else seeing the temps change when coasting down a hill.
    how can you argue with a guy on this who has a mountain in his avatar ? lol
    2014 A4 2.0TQ Technik
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  28. #28
    Senior Member Two Rings Quattro420's Avatar
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    [QUOTE=jfo;13526011]It may not be a problem, but I wouldn't say it's normal. I drive up and down mountain roads daily and have never experienced this or heard of anyone else seeing the temps change when coasting down a hill.


    I agree it’s not Normal I bet the thermostat is week and on normal operation the water pump load circulating the coolant is enough tho keep the thermostat closed, and on coast the load on the water pump circulating the coolant is less. Just an idea if it were my car I’d replace the water pump assembly and the union at the water pump.

  29. #29
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    With the downhill, the engine is not generating much heat. One thread I found was talking about comparing the temp drop when coasting down the hill in drive vs in neutral. I guess the engine has to load itself more in neutral. See if there's a difference.
    But what heat is generated can only vent one of two ways, the radiator or the heater core. If the temp drops below 90C, the thermostat should cut off the radiator.
    But if you have the heater or the defroster running, the heater core could be sufficiently removing the heat the engine is generating.
    I notice the heat seems to start coming out from a cold start once the coolant passes mid 60ish C, which is also the same point where ODB mode 6 gets enabled.
    But some thoughts to keep in mind.
    2009 A4 Avant 2.0T quattro Prestige, 182k miles

  30. #30
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    I think this is getting a bit overthunk. During normal driving, the needle should stay in the middle. If its below and comes back up or stays below normal, the thermostat is faulty and should be replaced.

  31. #31
    Veteran Member Four Rings jfo's Avatar
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    Quote Originally Posted by elscotto80 View Post
    I think this is getting a bit overthunk. During normal driving, the needle should stay in the middle. If its below and comes back up or stays below normal, the thermostat is faulty and should be replaced.
    ^^^ This. I have never seen the temp gauge move when going up or down hills in many, many years of driving unless there is a thermostat issue. And our summer temps here are often high 80's to mid 90's
    2011 A4 Avant quattro tiptronic/ Eurocode Sway Bars, End Links, Alu Kreuz/ 034 Catch Can/ Various VagCom

  32. #32
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    No idea why but the last 2 days I've been driving, the temperature sticks at 90. It doesn't change any more (even when coasting down a hill). I'll see if this changes in the next few days

  33. #33
    Established Member Four Rings Novarider's Avatar
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    Quote Originally Posted by jfo View Post
    It may not be a problem, but I wouldn't say it's normal. I drive up and down mountain roads daily and have never experienced this or heard of anyone else seeing the temps change when coasting down a hill.
    So if you coast down a steep mountain road stuck behind someone going slow it doesn't happen? I'm talking like 35 mph having to ride the brakes because the little old lady in front of you is. Your foot never touches the throttle. That's the only time I've seen it happen.

    During normal driving I've never seen a big fluctuation. It will go from right at the middle line to just below the middle line which I figured is the thermostat cycling.

    I can also idle for as long as I want and the needle never makes big drops or overheats.

    If neither of those are normal then I guess it's time I change the water pump.
    2011 A4 Avant Prestige S-Line

  34. #34
    Veteran Member Four Rings jfo's Avatar
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    Quote Originally Posted by Novarider View Post
    So if you coast down a steep mountain road stuck behind someone going slow it doesn't happen? I'm talking like 35 mph having to ride the brakes because the little old lady in front of you is. Your foot never touches the throttle. That's the only time I've seen it happen.

    During normal driving I've never seen a big fluctuation. It will go from right at the middle line to just below the middle line which I figured is the thermostat cycling.

    I can also idle for as long as I want and the needle never makes big drops or overheats.

    If neither of those are normal then I guess it's time I change the water pump.
    I can't say that I recall being stuck behind someone going slow down a long hill and also noticing the temp gauge. I can only confirm that I've never noticed my temps fluctuating under any conditions...going fast, slow, uphill or down during the 8 years I've owned the A4. Even when I'm down in Vancouver stuck in traffic, I don't see any fluctuation.
    2011 A4 Avant quattro tiptronic/ Eurocode Sway Bars, End Links, Alu Kreuz/ 034 Catch Can/ Various VagCom

  35. #35
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    Mine has been fluctuating when it is cold out too. I was thinking it was kind of odd. Most of the time it is when coasting down an off ramp (from like 75) but sometimes it does it when just driving on flat ground like was stated before. I am not sure if it is heater being given a priority or something else. My wife drove this car for the past 7 years so I am not sure if it did this before or not.

  36. #36
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    Quote Originally Posted by BrianC302 View Post
    Mine has been fluctuating when it is cold out too. I was thinking it was kind of odd. Most of the time it is when coasting down an off ramp (from like 75) but sometimes it does it when just driving on flat ground like was stated before. I am not sure if it is heater being given a priority or something else. My wife drove this car for the past 7 years so I am not sure if it did this before or not.
    A fluctuation temp gauge is telling you that the thermostat is on its way out. It should be replaced.

  37. #37
    Active Member One Ring EMon81VT's Avatar
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    Change the coolant temp sensor and/or the thermostat

    Sent from my VS995 using Audizine mobile app

  38. #38
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    Quote Originally Posted by elscotto80 View Post
    A fluctuation temp gauge is telling you that the thermostat is on its way out. It should be replaced.
    Thanks

    How do you know if it is the temp sensor or the thermostat?



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