4 Cyl Temp Sensors
Question: I was wondering if you might know anything about the temp guage. I don't get a reading from the guage itself. Also, the fan does not kick on. I started to turn on the AC to make the fan come on at all times, but I don't know if that's a good idea. It's a 5 speed with no AC compressor on when I bought it. I'm also told that there are 2 temp switchs on it - 1 for the fan and 1 for the computer, although my Haynes manuel does not back that up. Do you think the temp switch in the head may be faulty or should I look elsewhere?
Answer: There are 3 temp sensors on the head of your 85 L4 (as well as 84's & 86's). All are on the drivers side and form a sorta "halo" along the same line. The one that is hard to see is on the front of the head, points toward the rear window, and turns on the radiator fan when engine temps reach 223-224 degrees.
The one that points straight up is for the temp gauge. Turn the ignition switch to on, jump the sender connection (by a "U" shaped piece of wire or a paperclip, and watch the gauge. If it swings to extreme Hot, then the gauge is usually OK, and the sender is bad.
The sensor mounted in the themostat housing is for the ECM.
Think of it this way, front sender (called fan switch) is for the front fan, middle sender is for the gauge in the middle of the car, and rear sensor is for the ECM which is the furtherest toward the rear of the car.
87-88 L4's have only two senders/sensors - gauge and ECM (in the same locations). On these, the ECM turns on the fan.
Many autoparts catalogs/computers have the wrong sensors/senders/switches listed for our cars, so always compare what you are given with what is in the car. Do not use any kind of "plumbers tape" to seal these parts. New ones come with a non-insulating coating, or a sensor proof RTV can be used on one that has been removed and is being reinstalled..
Using the a/c controller to turn on the fan, with no compressor or compressor belt, will not harm anything. But, it should not be used if you have a siezed compressor with the belt still on.
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