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    Thread: Temperature gauge fluctuation?

    1. Member DasCC's Avatar
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      '13 2.0TSI | '14 1.8TSI
      11-05-2010 10:38 PM #1
      Hey so typically after driving for 5 minutes or so my temp gauge is in the middle at 200f. After about 15 min of moderate 35-45 mph driving it went down a notch below the 200 mark after it had reached 200f. I've noticed this happen a few times recently. Has anybody else had this happen?

      Sent from my ADR6300 using Tapatalk



      *Edit* thanks. I did notice that it happens while coasting downhill. I guess i'll be taking it it to my mechanic to take a look.

    2. 11-07-2010 08:57 AM #2
      Either your coolant temp sensor or thermostat is going bad.

    3. Member
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      '10 B6 Wagon in Mocha/Black
      12-14-2010 08:46 AM #3
      I have just had it happen today! On top of that the heating inside the cabin was mediocre, at best. The temperature outside was about 21F. My commute is only about 8 miles but in a moderate stop-and-go traffic so heating up should not be a problem. Even at Climatic set all the way to 80 I was not feeling the right amount of heat by the end of my trip.

      Same thing was happening to my 2002 B5.5 and it turned out to be a bad thermostat. I am not taking any chances this time and taking the Wagon to the dealer. Let's hope they will diagnose the problem without giving me the dreaded "Could not replicate the problem".

      Will provide an update on Friday.

    4. Member
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      12-16-2010 02:01 PM #4
      Quote Originally Posted by 2001 Variant View Post
      Either your coolant temp sensor or thermostat is going bad.
      Will any of these throw a code? My dealer just called me and said that there is nothing wrong with the car (see my post above). They measured the temp at different heat settings and it was all within the specs. The moderate tem fluctuations are, per the technician, within specs as well. No codes were found.

      I guess for now I will have to just live with that.

    5. 12-19-2010 01:56 AM #5
      Then I would guess bad thermostat. If it was the sensor you wouldn't feel heat fluctuation.
      The thermostat might work ok at times but not at others (of course the dealer looked at it when it was fine). Keep an eye on it and take it back when it happens more frequently. It should get worse over time. This really shouldn't hurt your car but monitor the engine temperature in case it does got too hot at some point.

    6. Member
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      12-19-2010 08:06 PM #6
      Quote Originally Posted by 2001 Variant View Post
      Then I would guess bad thermostat. If it was the sensor you wouldn't feel heat fluctuation.
      The thermostat might work ok at times but not at others (of course the dealer looked at it when it was fine). Keep an eye on it and take it back when it happens more frequently. It should get worse over time. This really shouldn't hurt your car but monitor the engine temperature in case it does got too hot at some point.
      Thanks! This is my plan as well. I spent two winters with my old B5.5 before I finally diagnosed the problem and decided it's time to have it fixed!

    7. Member
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      12-19-2010 08:37 PM #7
      VW coolant temp sensors are known to go bad.

    8. 12-24-2010 05:49 AM #8
      I recently had my water pump replaced, but i have seem to have temp fluctuations, it drives fine for approx 20 mins, then the temp gauge starts going up to 3/4 to the red line, then goes back down to 90 degs. Does any have a suggestion for this?

    9. 12-24-2010 06:29 PM #9
      Quote Originally Posted by posing_it View Post
      I recently had my water pump replaced, but i have seem to have temp fluctuations, it drives fine for approx 20 mins, then the temp gauge starts going up to 3/4 to the red line, then goes back down to 90 degs. Does any have a suggestion for this?
      Thermostat might be opening too late. Usually it will open to include the radiator in the cooling circuit after it reaches a certain temperature. If that doesn't happen your coolant doesn't get cooled by the radiator and thus gets hotter than it should. Then at some point your thermostat opens and everything goes to normal.

    10. 12-24-2010 08:30 PM #10
      thanks variant..
      do you think this is a major problem tough, or something that can be left a litle longer..?
      i just hope this wont burn out my engine?

    11. 12-24-2010 08:48 PM #11
      Well there is some risk to it.
      You have to monitor the temperature very carefully and stop/turn off engine as soon as it's getting too hot (before it hits max on the gauge - don't wait until it's all the way up).
      Also, if the thermostat is not opening it might at times get stuck open as well. This would mean longer warmup time for the engine and potentially poor performance along with higher fuel consumption.

      I think you're ok driving it if you have to but I would get it taken care of as soon as you can. If you notice the temp going up past center you could try to turn the car off for a few minutes which might give the thermostat enough time to open while you're not putting more heat into the system.

    12. 12-24-2010 10:30 PM #12
      thanks heaps. uve helped alot bro

    13. 12-29-2010 07:53 AM #13
      @2001 variant
      I replaced the temp gauge.. but its still doing the same thing..
      do you think its the head gasquet? but there are no signs of problems with it like no white smoke or milky oil stuff like that?

    14. 12-29-2010 10:15 AM #14
      Did you replace the coolant temperature sensor or the thermostat?

      I believe the thermostat is what is bad. It's the device that controls coolant flow into the radiator.

      If you replaced the sensor (sends temp reading to the gauge cluster and ECU) instead that's not a big deal either since they eventually go bad as well and now you won't have to replace it again any time soon and they are cheap and relatively easy to replace. The thermostat will be a little bit harder.

    15. 12-29-2010 06:57 PM #15
      my mate helped me replaced the thermo stat, and now the car is still doing what it was doing, he reckons that the next step would be going to do the head gasquet.. which i really dont wanna do as it costs a furtune..

      any suggestions on what i could do??

    16. 12-29-2010 07:25 PM #16
      If you haven't done the sensor yet I would do that first. It's pretty easy to do and cheap. When you get the sensor make sure to also get the o-ring and a new retaining clip in case the old one breaks.
      If your heat is steady while the temperature fluctuates on the gauge it could be just the sensor giving a wrong value. The sensor has two parts to it (really two sensors in one housing). One is just for the display and one is for the engine computer. If the display sensor is bad, the engine will run fine and won't record a trouble code but the gauge cluster will show false information. If you have access to VAG-COM or a similar VW service tool, you can compare the readings of the cluster and the ECU.

      Another thing you can do is get a flow diagram of the cooling system and feel the various hoses during while you warm up the engine and just after it goes to high temp on the gauge. Feel the hoses by the radiator (in and out) and compare temperatures. You can also take a thermometer and take accurate measurements. There should be a temp difference between radiator in and out and it should be hot on the in side.

      You might have a blockage somewhere in the system or maybe the water pump is bad (even if you replaced it recently could have been a bad part).

      I don't think it's the head gasket. Usually the gasket fails due to running the engine too hot for too long, not the other way around.

      Before you attempt doing the gasket or telling a shop to do it I would try the above or take it to a qualified independent garage for proper diagnosis. If you just tell them to replace the head gasket they will do just that, along with a hefty bill. It would be worth spending a few bucks on diagnosis before you dive in and do an expensive and complicated repair that might not solve your issue. If they come up with something simple you could still fix it yourself.

    17. 12-30-2010 10:26 AM #17
      hey thanks for your help variant...
      i recently drove it today and it just runs the temp up to near like 120 deg celcius after a good 15-20 mins?, but never goes down now. Stopped the engine and wait for it to cool down before driving again.

      The radiator hoses are hot on the right side and warmish on the front. So i think there is the ight coolant coming through, ive asked around and people say it might be the gasquet, or the cylinder head which will cost me a furtune. I really dont think it is the sensor, as it is not even fluctuating now. But my concern is that if i replace the gasquet it might not solve the problem, since the thermostat didnt solve the problem?

      Any other sugestions on what i should do?
      Sorry if im annoying but, im still a university student and a bit short on cash.
      Any help would be appreciated..

    18. 12-31-2010 08:19 AM #18
      Well, if the radiator supply is hot and the other side is cooler that should be all right. I would still replace the sensor as that is a cheap part and pretty easy to do. Not sure what engine you have but if you have easy access to the sensor you could unplug the connector and measure the resistance before you replace it or take it out (with cool engine - otherwise you'll get a nice fountain of coolant that will burn you) and throw it in some ice water and measure resistance on both circuits and then throw it in boiling water and do the same. Then compare to the spec values for the sensor.
      I would definitely do this before attempting the gasket.

      An alternative would be to have it diagnosed by a reputable shop.

      Another potential cause could be the radiator fan not coming on but this seems unlikely since it's winter unless you are in a hot climate and this issue happens during stop and go or slow driving (with lack of air flow.

    19. n00b rboss101's Avatar
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      11-02-2011 03:42 PM #19
      Not to steal you post, but I'have been experiencing something similar. My car warms up ok, but as soon as I turn the heat on the gauge goes down from 90C to 70-ish, and back to 90 after I trun the heat off. Also, the gauge is showing 90C and after looking at it with VCDS its showing less than that. The dial and the data from computer do not match. Any ideas?
      Again, sorry for doing this in your post.

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