Cooling Fan Test

Checking the Engine Cooling Fan Operation
by Jeff Korn and Pete Dunham

OK, here is the low down on the fan system on the 87-88 TC. Both fans are controlled by the EEC via the IRCM (Integrated Relay Control Module), which is the black box with about 24 wires coming out of it located on the front of the passenger's side strut tower. To test the aux fan (the smaller drivers side fan) pull the connector off the A/C pressure switch, which is in the high side A/C line near the VAM. Turn the key on, and jumper the 2 pins in the connector you just removed. If the aux fan runs, its relay in the IRCM is OK.

There is an easy way to check the operation of the main (pass side) fan. Run the KOEO EEC diagnostic test. During the test, the main fan should run. If it does, the IRCM, and all the main fan wiring is functioning correctly all the way from the main fan to the EEC. If the main fan comes on during the KOEO test, but fails to come on when the motor gets hot (stock temp gauge up about 1/2 way), the most likely cause is a bad ECT. If you still suspect the IRCM is faulty because the fans failed the above test, then do this before replacing the IRCM: be sure the heavy yellow wires going to pins 3 and 4 of the IRCM are hot at all times. These wires provide power to the fans directly from the battery thru fuse links "L" and "M". Test this with a test light, not a voltmeter.

Running a code test may show a bad ECT, but only if its temp readings are WAY out of wack. In other words, the ECT may be reading temp as lower than it really is, but still not set a code.

There is one relay for each fan in the Integrated Relay Control Module (IRCM) which is the big black box on the front of the passenger side strut tower. Also in there are the power relay for the engine control computer, the fuel pump relay and one other. At least one of our members has replaced relays rather than buy a new/rebuilt IRCM. From his verbal description it takes some electrical finesse. but I can't tell you more. I'll send him an e-mail and see if he will post something on it.

Here is some info for testing the relay for the driver's side fan.

Here is how to check the relay for the drivers side fan (smaller one) in the IRCM: Find the PINK wire at terminal 17 of the ICRM. Probe it with a pin, like when checking the TPS voltage. Run a jumper from the probe pin to ground with the key on. When the pink wire is grounded, the lower, drivers side fan should run. If the fan runs, the IRCM is OK. I have tapped into this pink wire, and use a relay to ground this wire whenever the HVAC function lever calls for A/C, so I have both fans running when the A/C is on. Motor stays nice and cool this way, and my 130A alt easily handles the load.

To test the other relay, do the above to the tan wire w/ orange stripe, it goes into the 2nd from the bottom position on the I/C side of the connector. Not 100% on that but I did this recently and I think that's the one.

Hello! I am having. Some issues with my radiator fans and have done a little trouble shooting but don’t know what to do now.

Right now, the car will go to the very top of the normal range and when above the half way point on the temp gauge the fans don’t turn on.

When I turn the key on, the main fan turns on for a split second then turns off again. I also did your pink wire test “Find the PINK wire at terminal 17 of the ICRM. Probe it with a pin, like when checking the TPS voltage. Run a jumper from the probe pin to ground with the key on. When the pink wire is grounded, the lower, drivers side fan should run. If the fan runs, the IRCM is OK.”

The fan did turn on, so I know both fans can turn on, so why don’t they turn on when the engine is hot?

Firstly, thanks for this article and the others. I'm new to the TC and trying to soak up the information.

I'm not having any cooling issues but I'm curious when the lower-drivers-side fan is designed to come on by itself under normal conditions. I am assuming the fans come on at different temperatures and in my experience the second fan has not been necessary. According to my infrared thermometer my main fan kicks at 220 or at any temp when the A/C is on. Since it has not gotten above 72 in Ohio since I bought the TC the temp comes down very quickly and I'm assuming that is why I don't see the second fan kick.

So, I think I'm really asking if the main fan should come on at 220 and when does the second fan come on - if ever?

Firstly, thanks for this article and the others. I'm new to the TC and trying to soak up the information.

I'm not having any cooling issues but I'm curious when the lower-drivers-side fan is designed to come on by itself under normal conditions. I am assuming the fans come on at different temperatures and in my experience the second fan has not been necessary. According to my infrared thermometer my main fan kicks at 220 or at any temp when the A/C is on. Since it has not gotten above 72 in Ohio since I bought the TC the temp comes down very quickly and I'm assuming that is why I don't see the second fan kick.

So, I think I'm really asking if the main fan should come on at 220 and when does the second fan come on - if ever?

The primary fan will turn on around 200-210F and off around 190F or if the A/C is on. The secondary fan turns on around 220F or if the A/C head pressure is 310 PSI. 

The  infrared thermometer has an error margin based on different factors, besides the fact the ECT is in direct contact with the coolant temperature and has its own rate.

I have an aftermarket aluminum radiator that cools the engine very well. I have never had the aux fan turn on in 23 years of owning my TC, and that includes driving at 75+ MPH in 100 degree ambient temps with the AC cranked up. I know the aux fan works as I have manual switches on the dash so I can turn on either fan if I want to.

Great info - Thanks.

I bought the car to drive it in the summer - tours and events - so I want to understand as much as I can about the cooling system and get ideas to stay ahead of potential overheating. Thanks again!

One thing to check on the cooling system: There is a small hose attached to a bung on the lower intake between cyls 2 and 3. The bung points somewhat downward. The ECT (coolant temp sensor if you aren't up on Fordspeak) is screwed into the intake directly above the bung between injectors 2 and 3. The hose on the bung flows coolant over the ECT. Not uncommon for this bung to get plugged with goo, especially if the cooling system hasn't been maintained well. If plugged, the ECT gets little to no coolant flow over it which will give the PCM incorrect coolant temp information.

Pulling the hose off the bung and rodding out the bung with a stiff wire, etc. will restore proper coolant flow over the ECT. The hose attached to the bung is likely original and should be replaced. OEM hose is a molded hose with a 90 degree bend at each end, but I just replaced my hose with bulk hose. Dont remember the hose ID off the top of my head.