Cooling fan issue

[BennSport]

Hey everyone, I’m having a cooling fan issue with my 83’ 944.the cooling fans only kick on once the water temp needle goes past the right hand line on the gauge. Would that be the thermoswitch? For more info there is also a small coolant leak above the blue radiator drain bolt.

[Tom]

I'd run through the Clark's tests, since it could be several things.

http://www.clarks-garage.com/shop-manua ... rlywithair

[944er]

That is correct behavior. My early 85 clicks on on the three quarter mark, and clicks off at just above the 1/4 mark (and has since new.) No issues with your thermostat. The leak is more problematic, you may need a new radiator.

[BennSport]

So this is not an overheating concern? Mine turns off at the halfway mark. I’ll need to check regarding the slow speed fan because I’ve been referencing the high speed operation this entire time. Sometime this week I will go over all the testing Clark’s garage shows and report back

[944er]

On early cars, the only low speed operation is to cool the radiator off after it is shut down. It never runs on low speed with the ignition on.

[BennSport]

So I drove the car this morning and the issue seems to be worse. I looked at my gage and the needle was between the 3/4 line and the start of the solid yellow overheating mark. I immediately turned my ac on as the fans weren’t activated and drove the rest of the way like that. Is it possible my thermofan isn’t the same temp as my thermostat? I replaced the thermostat last year with a wahler unit.

[Tom]

If you have a coolant leak, then you likely have air in your system. As the coolant leaks out, air leaks in to displace it, making the reservoir appear full even though the system is low on coolant and high on air pockets. Air in the system will cause the gauge and temps sensors to get erratic readings and can cause overheating. I'd start by bleeding the system and fixing the leak, and it if still overheats, then start looking at the other components.

[walfreyydo]

Your temp switch needs to be rated higher than the thermostat opening temp, otherwise the fans will kick on before the tstat opens.

Before going further though, the overheating issue, is that occurring while you are driving or while the car is sitting still, or moving slowly? If its the later (and not overheating while moving), then that would indicate an issue with the fans. If its overheating while at speed on the highway, thats likely an issue with the radiator, water pump, or air in the system.

Assuming the overheating is occurring while stationary/slow speeds, I would (highly) recommend you go through the fan testing procedure on the Clarks link above before doing anything further - there are a number of components that control the fans and based on your last post, you are guessing at what it might be instead of actually testing.

The fans should come on at approximately 92C (but this depends on what thermo temp switch you have in the radiator). The temp switch usually has the two temperatures stamped on them (which corresponds to low/high speed temp activation).

The gauge reads as follows:


https://www.clarks-garage.com/shop-manual/elect-19.htm


Components that should be tested (via Clarks instructions):
-fans themselves and/or wiring to them
-thermo temp switch in radiator
-fan relay
-fan resistors

Any of these failing can cause issues with the fans coming on at the correct time or temp, so its worth testing these. The fan relay is probably the easiest to test. If relay tests good, then remove and test the radiator thermo temp switch (less easy to test, may result in loss/replacement of coolant). Usually if the relay is good then the temp switch is bad (assuming the fans themselves, wiring and resistors/fan speed works properly)

Run through the tests, and report back, we can help you troubleshoot from there.

Here is the link again for the Cooling Fan troubleshooting page that walks through step by step the testing procedures:
https://www.clarks-garage.com/shop-manual/cool-01.htm

[BennSport]

The car only overheats at low/no speed. I’ll check the thermofan switch today and hopefully do some of the testing if I have time

[Tom]

The car only overheats at low/no speed. I’ll check the thermofan switch today and hopefully do some of the testing if I have time

If the switch checks out, and even if it doesn't, vent the system and see if it improves, at least until more air gets in.