PCMAX

I have a early '85 944 and have had some overheating problems. Everthing thermo/pump/coolant etc, seems to be working OK & the fans run when the thermo sw senses high temp, its just that they are on/off all the time in city traffic.
someone told me that one of the fans (left viewed from in the car) should run ALL the time & the other just cuts in when the temp is high or when the A/C is turned on.
Is this true??????????? If so could it be the relay (#1) not working? How do I check to see if the relay is good?

Thanks In advance
Peter

KuHL 951

Do you have the 3-blade or 6-blade fans? Your first fan should not come on until it hits a preset temp if it's an early 944; the 2nd fan comes on at the 3/4 mark or when the AC is turned on The 6-blade turbo fan conversion is the best investment I ever made in my 83. The temp gauge calibration on the early cars is sort of scary; it makes it look like the car is running very hot. The later cars run just as hot but Porsche recalibrated the gauge to make it look like it was running more normal. If your temp cycles between the 3rd and 2nd mark all the time the 6-blade fan conversion will eliminate the early 3-blade leafblower fan coming on everytime it hits the 3rd mark. The 6-blade fans and shroud can be picked up for less than $50 US and is worth every penny of it.

Porsche-O-Phile

I just swapped a set of 6-blade fans into my early '85. They're absolutely a direct bolt-in replacement - no modification of any kind required. They move more air and run quieter. I think the only drawback is they require slightly higher current, but I haven't blown any fuses yet. I think someone posted something about the exact current draws and the available circuit capacity a while back and the consensus was that it wasn't a problem. Field results seem to support this - there are very few cases of blown fuses. In fact, I can only recall hearing about one.

I'd consider a vended 931 header too if you can find one (I'm doing this tomorrow most likely). That'll add some cooling air.

Charlotte944

For an early car the fan operation is fairly simple:

1. Ignition on and radiator hot, BOTH fans should run at high speed.
2. A/C and ignition on, BOTH fans run at high speed.
3. Ignition off, radiator hot, Driver Side fan runs at SLOW speed.

When you are sitting in stop and go traffic and the A/C is not running, the fans should cycle on and off.

To get some peace of mind, start keeping mental notes of how the system is running.

For example, when you are "at speed" the dash temp gage should stay some where near the middle mark or below. In city traffic, the gage may climb to the 3rd mark and the fans should kick on.

NOTE: Keep in mind that as you add electrical loads (A/C, head lights, fog lights, and so forth) the dash temp gage may indicate slightly higher than before.

PCMAX

What would be the preset temp you mention. I'm sure I read this before somewhere.
All the other replies seem to indicate that the fans (both) will only run when the gauge hits the 3/4 mark or if the A/C is on.
If this is true then getting 6 blade fans will only serve to bring the temp down quicker once the gauge hits the 3/4 mark.

KuHL 951

I'm not certain of the pre-set temp for the 1st fan. Clarks-Garage,
http://clarks-garage.com/shop-manual/cool-01.htm, has a good write-up on all the parameters. The 6-blade fans are just so much more quiet and efficient that whatever the low temp kick-in point is for the first fan it will keep it away from the 3rd mark unless it's really hot and you are stuck in traffic. I live in a climate where it's Africa Hot and since the swap I have only had the 2nd fan come on twice without the AC. When fan 2 kicks in the temp drops very fast and the constant cycling of the old 3-blade design is eliminated. Be careful installing a low-temp thermoswitch at the same time as a 6-blade conversion, the fans will run much too often as the thermoswitch does battle with the thermostat trying to maintain a balance in cooler conditions.

PCMAX

2Tight
Thanks for the link.
Is the thermofan switch the one screwed into the left hand rearr side of the radiator as viewed from inside the car??

83na944

The temperature set point depends on the thermofan switch. I think stock is 92 C, but you can get switches that close at lower temperatures. I put a lower temp switch in at one time, the fan ran almost constantly, so I'd stick with stock if I were you.

The left fan cycles, the right fan runs anytime the ac relay is energized.

I understand that when the thermofan switch senses a higher temperature, it kicks the left fan on high. I have no idea how this could occur because there are two wires going to that switch. One is hot , the other goes to the fan. So I don't understand how the switch can get the fan to high speed or turn on the right hand fan, for that matter. I guess this only happens when the ac is on.

Charlotte944

The early and late fans operate differently.

For early fans:

1. Ignition OFF, radiator HOT: Driver side fan runs at SLOW speed. Speed is controlled by a resistor in series with the fan.
2. Ignition ON, A/C OFF, radiator HOT: Both fans run in HIGH speed. Fan relay jumpers resistor and connects second fan.
3. Ignition ON, A?C ON: A/C relay turns BOTH fans on HIGH.

NOTE: The radiator switch is a Single Pole, Single Throw swithc, so its either open or closed.

For late cars, fan speed is controlled by the Fan Relay which gets inputs from the radiator switch and the A/C system High Pressure switch.

Both fans run at SLOW speed when the ignition is OFF and the radiator is HOT.
Both fans run at Slow speed when radiator switch closes the low temp contacts.
Both fans run at HIHG speed when the radiator switch closes the high temp contacts, or when the A/C system HIGH pressure switch is closed.

PCMAX

I ran through the tests in the Clarkes Garage manual and it looks like i have a bad "slow speed resistor"
The manual says "Locate the slow speed fan resistors on the firewall behind the tachometer" as I have a RH drive car does anyone know if thiis resistor will be on the firewall on the LEFT of my car or will it still be behind the tacho on the RHS?
I would also appreciate a picture of this resistor so that I at least know what I'm looking for.

Thanks for the help so far!!!!!!!!!!!