Granite 944

Ok, I go out to the garage to get "SWEET P" out for a run, open the door of the garage and hear something running real softly under the hood of the car. Yep....its the drivers side cooling fan barely running! Yep, the battery is so dead I don't even hear it click off the starter solenoid. Well, I know from the info seen here, and at Clarks Garage that I can almost certainly figure that I need to replace the thermofan switch. I also need to retention the timing belts within about 500 miles. I'm also considering changing the stock three bladed fans to the six bladed ones. Are the six bladed fans REALLY that much quieter? My current fan operation has always been noisy, but also the drivers fan always goes directly to fast speed when thermofan switch calls for it. Only runs in slow speed when the ignition switch is off, but normally not for very long. The drivers side fan is suppose to go to fast speed when a high temp. condition is called for by the thermofan switch, whilst I'm driving down the road...........right? No slow speed in between there anywhere. Lately, the fans have been running alot while driving. (never goes over the 3/4 mark). AC always off.
I'm thinking of purchasing the thin walled wrenches (9244) from Bruce at arnnworx.com to do the belts with (I put new belts on about 2k ago without these wrenches when the engine was out of the car). I intend on installing a used thermofan switch (tested according to Clark's Garage), installing the six bladed fans, and of course, retension of the belts.
One other thought......has anyone ever experience this cooling fan running on and on like this, only to discover it was caused by a very weak battery? Any thoughts, suggestions or comments gladly appreciated!

EZRider

Hmm I don't know about a weak battery causing the fan to run-on. If the thermo sensor is bad it could ground out permanently which could cause the fan to runon. Weak battery usually the end result of problem elsewhere or just the battery being tired and worn.

SoCal Driver

Early fans do not do the two speed business that the later fans do. This is a function of a three prong temp switch and a $150 relay. The pre 85.5 set up will turn one fan on or both fans on depending on the AC setting.

The six bladed fans are nice. Besides being quiet they have sealed bearings and a different (better) brush/armature design. Try getting the shroud and a good part of the wiring harness too. Seen them used for about $50 on eBay.

gtroth

My thermofan switch recently failed that way, draining the battery. I got quite good at pulling the fan fuses everytime I stopped for long until I could get to fixing it (I hear pulling the fan relay is also popular). There's a chance that the relay failed, so what I did was put my new switch in the circuit, just hanging it there by the connector to be sure the fan went off before going to too much trouble.

EZRider

The six bladed fan is from the later model 968 series? Or is it after market item?

SidViscous

"Early fans do not do the two speed business that the later fans do"

Why does everyone keep saying this. Mine does, and I don't think it's modified in anyway.

Granite 944

Thanks for the replies!

This is what I thought, and glad to have you confirm it!

I only asked about the battery because I did charge it back up, and when I re-connected it, the fan did not come back on. Also, I had a honda car do this once, and it was due to a bad battery/lowvoltage signal. (sure the sensors are quite different though).

Granite 944

Sid, does your fan run the drivers side fan at low speed at some point while your driving the car? Or is it just after key is off?

SidViscous

Always when the key is off. Sometimes when running. Depending on temprature.

Granite 944

I've never noticed the drivers side fan running at slow speed while the engine is running, but I'll sure look for it after I've replaced the fan switch. Thanks

Charlotte944

For the early cars the ONLY time a fan runs at slow speed is when the radiator temperature switch is closed (radiator is hot) and the ignition is off.

The driver side fan is wired through the temp switch and a resistor. When the switch is closed current flows from ground, through the fan, through the resistor and then back to the battery.

When the ignition is on, and the temp switch is closed, the fan relay jumpers around the resistor and connects both fans to full battery voltage so both fans run at full speed.

When the A/C is on, the A/C relay controls the fan relay, and both fans run at high speed.

For later cars the fan speed is controlled by the fan relay. The fans will run at slow speed whenever the low temp contacts in the radiator temp switch are closed regardless of whether the ignition is on or off. The fans will run at high speed if either the high temp contacts in the radiator temp switch are closed, or if the A/C refrigerant high temp switch (which is actually a pressure switch on the high pressure side) is closed.

Typically the fans will run when ever the radiator is "hot" and the car is moving slower than about 35 to 40 MPH with the A/C off. Above those speeds there should be sufficient air flow to keep the coolant temperature below the switch set point.

The six blade fans are quiet because they have more blades than the early fans, just like a Hughes 500 or a BO-105 rotor head makes less noise than a Hughey or a Bell-222.

If you go with late model fans, make sure you have enough clearance between the passenger side fan and the lower radiator hose.

I put a late model fan in my previous '84, and two days later the fan cut through the radiator hose. To "fix" the problem I put the late fan on the driver side. Also, the late model fans have the electrical connections in a different orientation than the early fans, so you may need to use some nylon wire ties to keep the harness out of harm's way.

Granite 944

Thanks for all the good info Cliff. I found a TSB that covers making the conversion from 3 to 6 bladed fans. It does mention about using a newer style lower radiator hose, or shortening the water pump side of an old hose by 5 to 10mm to provide the needed clearance. I see it also mentions about the electrical connectors and the positioning of elect. plugs also. Now I just got to watch what degree of thermofan switch I put in. I've got a 192 degree thermostat in the car now. I'm not sure of the temp. range of the thermofan switch thats in the car now. I know the FSM shows a 92/87 C (198/188 F) switch. (same as in Clarks Garage). I have a 82/77 C switch from a parts car (I'm thinking 180/171 F degrees is gonna run my fans all the time.) I just ordered a 209/199 F (I think. Gotta check it again tommorow) switch from my local parts house.(I think the car is gonna run to hot with this one). So I think I'd better find the stock (92/87 C ) switch, or replace my thermostat with a 160 degree one, and use the 180/171 F switch. I'm sure the fans do operate (if working properly) just the way you stated above. I've just had some strange stuff going on with the fans for a while. Thanks for the re-assurance!