Another attempt to gather information on an overheating problem on a 1991 Audi 100.
Fan switch --OK
Fan motor when bypassed -- OK
Thermo sensors in top goose neck -- OK
But when running car temperature gauge will indicate above mid-point; at this point I would assume the fan should kick on and cool the fluid in the system but it does not.
I need assistance in resolving problem.
Any suggestions or sites that may be of help would be appreciated.

Thanks,
Mikerike

 

I have the same problem, I asumed worst, Radiator, so i'm changing it now
its a PITA, have to remove AC and a lot more.
oops forgot, thermostat may not open fully.

 

According to my Owners manual the mid-point is normal or even to the right provided that the over temperature light doesn't turn on. BUT running at this point will cause the radiator, heater core and expansion tank to fail rather quickly as the stock expansion cap is 17-22psi.

Check the Lower Air Duct, it is made from crappy material that doesn't last long. Once it disintegrates little air is redirected towards and through the radiator. I have seen a lot of 5000/100/200 models were this is the case. I have made my own out of sheet metal and right away it made a difference. You also want to check the radiator and AC condenser to make sure that you can see through them and they are not blocked. Another problem is the multifunction temperature sensor, it is prone to corrosion and failure giving you no or wrong readings. The Fan thermoswitch is dual temperature OEM is 95/102°C, I replaced mine with 85/92°C and replaced the stock OEM 87°C thermostat with 80°C. This keeps the needle on the low side.



[IMG]local://upfiles/1095/77FD1948CCFD40D19527B0E76CDFC213.jpg[/IMG]

 

offramp your 85/92 fan switch, does it make your car run too cold and alwas fan on. or what?
I have overheating problem too, I changed my rad and still heating up.
its runs right in the midle, 90deg to the ground. the temp gage

 

85/92 fan switch keeps things nice and cool especially when you are sitting in traffic with the AC on. Since the thermostat is also lower temperature the fan doesn't stay on all the time. When I was using the OEM setup the fan cycled on/off way too often. When you changed the radiator did you change the thermostat? Did you check the connector for the temperature sender? Often the contacts corrode.

 

I already changed themostat to a 176* (80*) instead of the 87*.
The issue I am having is the fan is not kicking in once the temperature rises above the mid point.
Does your manual indicate what the temperature is when the gauge is at mid point. With this informatin I could calculate at what temp the fan should turn on in relationship to low speed and high speed dependent on the dual temp fan switch sensor.
If all else fails I'll hook fan to "hot" with ignition in on position essentially ignoring fan thermo switch.

Thanks
Mikerike[8D]

 

Offramp,

I havve not change the fan switch but if I decide to go to a lower temp one as you did, where might I locate(buy) the alternate switch.
Do you have a preferrd place for parts?


Mikerike

 

The owner’s manual doesn’t show any pictures for normal temperature.

Changing the thermostat and not changing the fan switch is not going to do much especially if the lower air duct has disintegrated and you are going +60MPH or standing still. The water will have to warm up to 95C before the fan kicks in.

You can get the lower fan switch from rockauto.com, blauparts.com, thepartsbin.com, etc.

 

Heres my sitiuation. all stock, thermostat 87C, thermo switch 95/102, water pump stock, etc..., Ah radiator is made intarly out of aluminium.
As in the picture, First dot is when I drive, I consider it Normal.
Third dot is when fan kiks in, and second is when it turns of.
Oh I think I got it, No first Speed, I will have to varify that.

[IMG]local://upfiles/10191/2DC663AE0CA7408495DFAE0CE0A6561D.jpg[/IMG]

 

Okey I have it weared. at evning fan turns way below, at the second dot and turns of at first dot. and turns some times into first speed too.
also if I drive it then stop and go higway then fan turns at low temperature as it suposd to be.
it works at random