'79 aux fan not working

[Rupesy]

Just looking for some confirmation. My aux fan does not come on when the temp gets to the red warning light. I don't have the a/c working at the moment. According to the wiring diagram should come on when either the a/c is on or high temp condition. I have directly hooked up the fan at the main connector and it works fine. I have also jumpered the temp switch at the bottom of the radiator and it works fine. This lets me know the relay and fuse are OK. So this leads me to believe the temp sensor does not work anymore and needs to be replaced. Have I missed anything?

[Rupesy]

I see a 92C and 75C switch and they are really cheap? Which temp is recommended??

[Maleficio]

Have you looked at the schematic yet?

By the way, my fan stopped working a few months ago. Then I remembered I had moved relays around trying to fix a no-start. Put the right relay back into the right slot, tadaa, working fan.

[Anthony10370]

You may want to verify the operating temp. It could be a bad gauge sender or something in the gauge circuit causing the gauge to read hot when the actual temp is fine.

If the gauge happens to be correct you may want to look at the cooling system, (viscous fan, radiator...) to find why it's overheating in the first place. I think after 35 mph there should be enough natural airflow to keep the engine cool without the use of the fans anyway. So if it's overheating on the freeway either the gauge is wrong, or the radiator may be plugged.

Good luck-
Anthony.

[Rupesy]

Here is the issue. The car normally runs with the needle on the 1/3 mark and during normal driving around it does not move much from that spot. I don't have any overheating issues. If I let the car sit and idle for about 15 minutes, the temp slowly creeps up to the 2/3 mark and the red light goes on. The car starts to run bad at this temp and so my best guess is that the temp gauge is fairly accurate. The reason why I am interested in getting the fan issue fixed is in the case that I am in heavy traffic and have to inch along, I want to make sure I don't have overheating issues. I am certain that the circuit checks out fine because it works fine when I jumper the temp sensor. That means that the relay is sensing the ground and closing the fan circuit allowing it to run. For $10 I can get a temp switch, I am just wondering which one would be better since I have no clue what the normal temp should be on this engine. The 75C seemed a little low. What is the normal operating temp for the engine???

[Maleficio]

I replaced my temp II switch thinking it controlled the fan, but it doesn't. The switch at the bottom/right/front of the radiator is what provides ground to the relay which powers the fan.

[MPDano]

Originally Posted by Maleficio

I replaced my temp II switch thinking it controlled the fan, but it doesn't. The switch at the bottom/right/front of the radiator is what provides ground to the relay which powers the fan.

Exactly, you can just bridge the wires that connect to the switch (use a small wire with 2 spades). If it turns on, then it's your Temp Switch. I think the key has to be on, on your ignition.

[tmpusfugit]

It seems unusual that you would need the aux fan to come on at all if your belt driven viscous coupled fan is working correctly. It was 107 degrees here today, stop and go driving in my '84 never went above the 2nd white line, and the aux fan did not kick on....

My neighbor had a similar problem in his car, we replaced the belt driven fan with one out of a parts car...problem resolved. It sounds like yours might be getting low on the viscous fluid, which others have successfully replaced in their fans

The aux fan not working is another problem, but IMO not the root problem...

[Mrmerlin]

FWIW the aux fan will come on without the AC system energized,
however the radiator switch must be working for this to happen.

As others have posted check the aux fan relay and its fuse ,
then check the switch on the front of the radiator to make sure the wires are connected,
and to test the system ,
you can touch the wires together with the key on then the fan should run

[Rupesy]

I agree that this is not addressing the root of the problem. Will check into the belt driven fan later.

Thanks for all the other tips....I really think it is just the temp switch...which temp? 92 or 75

[Maleficio]

My AC doesn't work, my belt-driven fan has no belt, and my electric fan operates just fine after I figured out that I had swapped relays to the wrong spots.

[rjm65]

I have a weak fan clutch on my 79, works ok but not as great as the one on MPDano's Euro for example. I have the aux fan come on anytime the AC is on too.

With AC off it can get pretty close to the 3/4 mark unless the car is moving.

I replaced the existing temp switch with the 75C. Sometimes the fan kicks in automatically at the half way mark, other times the gauge will be up around the 3/4 mark and the fan doesn't come on. Turning on the AC kicks the fan on and always gets the temp down to at least the half way point really fast. Just can't seem to get consistent operation of the aux fan off the temp switch. Might be the location of the temp switch, I dunno.

If all's working well, you should be able to sit at an In n Out drive thru in the middle of summer in Death Valley, blasting the AC, waiting for your Double Double Animal Style without any overheating issues. These cars have a pretty robust cooling system.

[Maleficio]

Royal Purple sells a serious coolant additive. Last fall I had trouble getting my 82 to fully warm up. Yes, new thermostat.

[Rupesy]

rjm65,

never thought about the location of that temp switch. The fact that the cooling fan switch is located at the bottom of the radiator where the coolant is the coolest and the gauge temp sensor is on the block may explain why the cooling fan comes on at different spots on the temp gauge....hmmmmmm....the temp fan came on only one time so far in my diagnosis. It was after I shut it down as it was approaching an overheat. It sat for a minute and when I went to start the engine again, the fan came on as I turned the key.

Anyway, based on your explanation, I think I will go with the 75C to try it out. Maybe I have the 92C.

Regardless, I totally agree that I have to hunt down the root of the problem here, but for now I just need to buy myself a little time.

[Rupesy]

By chance, does anyone know the temp correlation (approximate) of the gauge marks (1/3, 2/3)???

[dcrasta]

Originally Posted by Maleficio

I replaced my temp II switch thinking it controlled the fan, but it doesn't. The switch at the bottom/right/front of the radiator is what provides ground to the relay which powers the fan.

My car had corrosion on the connecters under the rubber boot. Broke out the dremel , copper wire brushed them for a few seconds, used some De-ox on them and never had a problem since.

[Rupesy]

Just a follow up. I replaced the existing temp switch with a 75C and it comes on just above the 1/3 mark and keeps it there which is good for now. I was having some issues with overheating (going above the 2/3 mark) now that I sit in traffic a lot in Houston. I know this is not the real fix. I am just buying time until I can get around to replacing the fluid in the clutch fan.

[ice-hot]

Rupesy,
I have a "79" us auto, Porsche dealer sold me the 92C or it was 95C can't remember. Any way if you have the old one still it will have a number stamped on it somewere 92 or 75. Both mine had the number on them. I would be interested to know what yours had in it?
John

[Normy]

If you want your aux fan to come on whenever the ignition is on, pull the connector at the lower drivers side of the radiator and jumper the two terminals. From then on, your aux fan will run when the key is on.

This fan is more than capable of replacing your belt driven fan, it is all your radiator needs even in extreme temperatures in traffic.

N

[Rupesy]

ice-hot,

the side is stamped with 92/87, I'm pretty sure right now that the switch worked and it was a matter of cleaning the terminals. I just didn't like the fact that it came on at such a high temp.

Normy, thanks for the tip....I may end up doing that and getting rid of the belt fan.