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Rick_Leuce
08-06-2014, 01:08 PM
HI all,

The radiator fan on my 1991 SC does not turn on when the car is up to temperature. I tested the fan motor by connecting it directly to the battery, and it comes on. I replaced the temperature sensor that connects to the IRCM Cooling Fan Relay. I tested it by letting the car idle in the driveway until the engine heated up past the "M" in "NORM" on the temperature gauge, the fan still would not come on. I turned the A/C to full blast (which I hear is supposed to make the fan come on, even if the engine isn't up to temperature) but the radiator fan still would not come on.

I checked all of the fuses and replaced the IRCM relay with both a used one that was from a 1990 Thunderbird SC as well as a brand new one off of the internet, the fan still won't come on when the engine gets hot. The fan WILL come on if I unplug the cooling sensor, it will run at full blast as long as the car is started. However, the car will not start when warm if the sensor is unplugged (such as right after fueling up at a gas station). So starting the car as is, requires plugging the sensor (to start the car) and before leaving, unplugging it back in so that the cooling fan will work. The car can however start with the sensor unplugged if it hasn't been running for a few hours.

Assuming that the IRCM and Fan motor are fine, I was wondering what else I should check/replace to get the fan to come on as it's supposed to.

KMT
08-06-2014, 01:18 PM
I tested the fan motor by connecting it directly to the battery, and it comes on.

Did you test both the low and high speed circuits?

Did you check for any error codes?

jjklongisland
08-06-2014, 02:09 PM
Wow, does this sound familiar... I feel your pain. Turns out I had similar issue. Replaced with 2 IRCM's, ECU. sending units etc... Turns out it was my low speed fan was dead. The hi speed would come on but only around 229. Too hot for my liking. Invest in a real temp gauge since the stock one sucks...

KMT was real helpful also...

S_Mazza
08-06-2014, 02:32 PM
Have you tested the coolant temperature sensor to make sure it is reading correctly?

Rick_Leuce
08-09-2014, 04:08 PM
Have you tested the coolant temperature sensor to make sure it is reading correctly?

It appears to be reading correctly...

I measured it with an ohm meter...it was 13.5k a couple mins after start and counted down consistently to 10k, then I plugged the connector back in.

I measured it again when the temperature gauge reached the 1/2 way point (between the "o" and "r" in "norm") by unplugging the temperature sensor connector. It measured 2.71k. The fan turned on at this point and the meter started counting back up and stabilized at 2.91k.

This seems consistent with a 190 degree thermostat based on this chart:
http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0996b43f/80/20/2a/c5/medium/0996b43f80202ac5.gif

Les Borda
08-09-2014, 09:44 PM
I believe when you pull the connector off the coolant temperature sensor the high speed fan kicks on, in an old post of mine myself and club member came up with a variable resistor in parallel with ECT and we could adjust when we wanted the high speed to come on. It worked on my XR7 but we abandoned it when some more knowledgeable club guys said fooling the EEC on actual engine temp may result in it adjusting to air-fuel too lean...opps...well it was a good idea LOL

KMT mentioned a few posts back have you checked the low speed winding of your fan motor. You checked the motor with a direct battery connection but be sure both windings are ok they are distinct and separate.