I notice my 91 passat car temperature rises 1/4 above the midpoint when I'm driving slowly or idling too long. When I'm driving faster it goes down below midpoint.
The electric fan comes on when the temperature guage is a 1/4 above midpoint...then shuts off after a few minutes.
Im wondering if the temperature gauge is a little faulty or the car is in fact overheating at lowpeeds due to cooling fan not turning on sooner or bad sensors, or a bad thermostat.
Any ideas?
Thanks, Michael

 

It may be as simple as you need a thermostat. You also may need to find out if the fan motor is going out. I don't know but if there is a sensor for the fan it may be going. I'd recomend checking out the water pump too. I had the same symptoms on an 86 Audi and the pump went out on me. Way too expensive! If I had known to check it I could have replaced it for a few bucks instead of the redone head for the warpage.

 

Thanks, How would I go about checking if its the waterpump without
taking it apart, or checking if its the thermostat?
Michael

 

The thermostat should be simple, it isn't expensive so I'd just change it out and run the car in the conditions you mentioned and see what happens. To test it if you have a thermometer at home take out the thermostat and put it in water that is the same temperature as the thermostat is set for and it should open up. if it doesn't it is broke.
BTW changing your coolant might have an effect too. If it is too old or has too much water in it, it won't work as well as it should at exchanging heat. This problem could also indicate a clogged radiator. It should run in a very specific temperature range, if that is off then you have information. With a new thermostat it would indicate a clog probably in the radiator. If you decide to change the fluid flush the system out. (ask a mechanic)
As far as the water pump goes; If after you make sure the coolant is ok (i'd change it to be sure) and putting in a new thermostat it still does the same thing I'd talk to a mechanic. The mechanic should be able to tell you how to check out the pump. If he responds to your asking how to check it by asking you what it's doing w/o responding to your question beware. I'll look online to see what I can find.

FOUND IT! HERE'S A LINK TO THE PAGE LOOKS TEDIOUS BUT EFFECTIVE. http://autospeed.com/cms/title_Water...8/article.html

I am not recomending you buy one but here is a page with several pumps so you can see what you are dealing with.http://www.drivewire.com/products/vo...ter-pump/7355/

 

OK THANKS,
Yea the fan doesn't come on until the temps at 100C, then its only low speed for a minute then it shuts off. Not much help.
I hotwired the fan and both speeds are working although Ive never heard the 2 speed before going on automatically. With the fan hotwired to fast speed the temperature goes right down to below 90C normal when idling so I'm thinking thats the cause. Im going to replace the thermoswitch, see what happens. Radiator seems fine, no cold spots. I'll do a flush and change the coolant, put a new thermostat in too, Michael

 

I would for sure change the coolant from the symptoms you are disrcribing. A way to check your water pump with out removing will be some what errornous because you need to check the bearing and with having the timing belt on the pulley you won't get a accurate check. To really check it you would need to remove the belt and if you do that you might as well take the pump out and hold the housing firmly in your hand or a vise and try to wiggle the pulley. You shouldn't have movement if any it should be minimal movement. It is pretty cheap to do all of this the water pump, coolant, thermostat. This will prevent costly repairs. Good luck.

 

Yes the fan! I also had to replace it in the Audi I mentioned.