Questions and Answers

Mercury Sable Cooling Fan Doesn't Run Q. My name is Brian and I have a 1989 Mercury Sable that I bought new and still driving today. The problem is that the car now overheats and can't seem to figure it out. Flushed the radiator done, changed thermostat done, changed leaking heater hose done, put brand new hoses top and bottom done. But I noticed the temperature gauge isn't working properly and that the fan isn't kicking in at all.

I took a wire and jumped the fan switch and motor is still okay. I also spent a fortune and changed that big sensor on top of the radiator. Still overheats or should I say gets hot so I shut it off. I checked to see if It has a blown head gasket and no water in the oil as far as I can see.

One thing I forgot to mention was I did put stop leak in before I realized the heater hose was leaking. Is it possible that the sensor that measures heat is coated with that junk and I may need to replace this? Any suggestions would be great. I have three other cars but she has never let me down yet. 103,000 miles and hopefully many more!!!!

Brian

A. You didn't mention engine size, so I will assume it is a 3.0 liter V-6. The 3.8 liter V-6 may or may not be similar.

There are two Coolant Temperature Sensors. One is the Coolant Temperature Sender (CTS) for the temperature gauge in the instrument cluster and the other is for the Powertrain Control Module (PCM). The one for the gauge has a single red/white wire. The Engine Coolant Temperature (ECT) Sensor has a light green-yellow and a black/white wire.

The ECT sends the engine temperature to the PCM and the PCM turns the cooling fan on through the Integrated Relay Control Module (IRCM). The IRCM interfaces with the Electronic Engine Control (EEC-IV) system to provide control of the cooling fan, A/C clutch and fuel pump. The module also contains the EEC power relay to provide power to the EEC-IV system.

At this point I would just replace the ECT. It is fairly inexpensive and easy to replace. I'm pretty sure this will fix the problem. If not, then I would suspect the IRCM is bad.

I think that "big sensor" on top of the radiator you replaced is the IRCM.