Fan switch / Thermostat matching
 

Folks,

Just picked up a really clean '84 944, with proven 67K miles, nice, am sorting things out.

One of the concerns is the radiator fans are on much of the time, almost all of the time, and I'd like feedback from the group if in fact this might be expected given the cooling system setup.

Happens when:
- even when the days are in the 50s and 60s
- around town or freeway.
- the temp gauge is about 1/2 way, at the middle tick mark, when the fans come on, or just slightly above the middle tick mark when the needle is perhaps 1 or 1/2 needle width beyond the middle tick mark (at this point let's assume the gauge is correct).
- coming home, I lift the hood, and there is no abnormal under hood heat (compared to other cars I've had or have seen run hot)
- there are no leaks
- I bled the system as a precaution anyway, but no improvement.

I checked a previous repair record, and it appears the parts installed are:
- fan switch is part number 823.959.481 (repair order says "82 degree", so I think it is probably part number 823.959.481.D (77-82 degree). The next one up is the (87-92 degree) switch, so if the repair order says the "82 degree" was installed, it must be the low temp switch.
- the thermostat that was installed is "056 121 113A" which appears to be an 80 degree thermostat (a VW part number).

So both of these are at a fairly low temperature. I can't imagine an engine running any lower than these temps. So i am thinking this is the reason the fans are on all the time.

Now I did read as much as needed on the forum here so I could learn some more. One post suggested it is good to have things running cooler. But the problem is:
- having fans on essentially all the time is noisy and annoying.
- it gave me a lot of concern that something else is wrong with the cooling system.

So my plan is to move to the high temp fan switch (823.959.481.F) to keep these thing from coming on so much. A cooling system flush is probably in order as well since I am on the subject. Any comment from folks experienced with these issues? Really appreciate the help.

Certainly if you have a higher thermostat and lower fan switch they are going to run almost all the time. The other thing to consider here is....is the a/c compressor running defrost or otherwise? If so, changing the fan switch won't make a difference as the a/c relay is supplying the ground. If the fan noise bothers you, then you can raise the fan switch, just understand that your engine will run hotter. If you can live with that, then you have your answer. The other factor in that equation is where you live. If you live on the north pole, then certainly running the higher fan switch makes some sense. If you live in Houston, Texas, then changing the thermostat to match the fan switch probably makes the most sense. My personal preference would be to change the thermostat....but I live in Houston!

Tom,

Thanks for the answers. I live in the San Diego area, so not too hot, except a few weeks in the summer. Not sure I followed the A/C issue, I haven't been using it.

Again medium speed freeway driving tonight in 50 degree weather, the fans are on, the temp gauge is just a hair above the center tick. Can you or someone confirm if this is an approximately correct place for the temp gauge to sit? Cause I can't tell for sure if the car is running hot, but all the evidence suggests it isn't, that is why I think of going to the higher temp fan switch. If it is running hot, then this is important for me to know as well. Thanks.

fwiw:
my old '84 would run about the 1st line. a needle with above and the fans would come on, even while idling and would pull the temp below the line and the fans would go off.

check to see that both fans are pulling air thru the rad, rather than pushing it.

i changed the fans/shoud to the later, 6 bl config and when i shut the car off, the drivers side fan would stay on, pulling the water temp down and then would shut off.

the later cars were bursting hoses and went to a different relay to make this happen.

If I remember correctly when the a/c is on, the fans run also no matter the temp. That's what I meant with the a/c question. Basically just know that if you turn your a/c on or your defroster, the fans will run and that's by design. It's your choice which way you do it but it's probably not best to have them mixed or your fans will run when they don't really have to.

Tom,

Thanks! Now I got it. No the A/C is definitely not on. I don't think I even have to check the wiring or electrics for that possible source. The radiator fans only come on once the temp gauge is at the center tick mark. Bearone (Island boy), [hope this is the correct name] gave me good additional insight by mentioning his '84 would go only to the first tick mark when at operating temperature. Whereas mine goes to the next tick mark (the center one) as normal operating temperature. I do think the cooling system is probably not operating efficiently somehow, maybe the thermostat is old already after 4 years, maybe the cooling system needs a good flushing and is full of gunk. As you mention, I don't want the fans running when they don't have to, and freeway driving in 50 or 60 degree weather should not require fans even if I have the low temperature fan switch.

Roland