Fan stays on

[curtisgrace606]

My fan comes on as soon as I turn on the key and never goes off. Do I have a bad sensor in my thermostat housing? Also would this affect my gas mileage from running to cold? I'm only getting 29 mpg but the car seems to run fine.

[festygramps]

Running too cool will cut down your gas mileage. I've always liked old cars but when I start having problems with fan circuits I change them over to manual operation. It's easy and cheap.

[bravekozak]

year + carb or EFI + manual or auto + A/C equiped?

[curtisgrace606]

It's a 93 l. 5 speed with no a/c.

[curtisgrace606]

I was going to buy the sensor but is was $52.00. I was going to see if anybody had any suggestions first.

[festygramps]

Are you mostly a city or highway driver? I drive mostly highway so a manual switch is no big deal. If you drive mostly in the city, I'd probably change the sensor if you're sure that's the problem.

[bravekozak]

The cooling fan temperature switch energizes the solenoid in the cooling fan relay by closing above 207° F.

The yellow red wire also goes to the ECA. I would have to look up what the computer does. I hope it doesn't provide an alternate path to ground.

[crazyrog17]

The cooling fan temperature switch energizes the solenoid in the cooling fan relay by closing above 207° F.

The switch is normally grounded, but breaks the circuit to ground when above temperature. If you unplug the switch, the fan would trigger and you can touch it to the head to see it stops when grounded.

[curtisgrace606]

Im a hillbilly, it's all bad roads and hills. I took the sensor out and it broke into. I glued it back together and stuck it in. The fan was working so I thought I fixed it but I guess not. I'm not sure how it was before it broke because I had just got the car when it happened.

[curtisgrace606]

So you think that it's not got a ground to start with. I never considered that . It makes a lot of sense. I'll go and try that.

[curtisgrace606]

Ok I grounded it to the head and sure enough it quit. Man you guys sure know your stuff. So does this mean a bad sensor, relay or something else.

[festygramps]

I'm a hillbilly too. And I like it. A bad ground would be easy to fix. Hope that takes care of it.

[getnpsi]

If the switch was moved into the top radiator hose and a gauge was placed where switch was will fan come on later or earlier I assume later?

[curtisgrace606]

Is the initial ground in the sensor itself or is it elsewhere?where u from festy gramps? I'm from eastern Kentucky.

[bravekozak]

You are correct. The sensor switch is grounded when cold. The diagram shows both the switch and relay normally closed.
That means the solenoid in the relay is energized and held open until the temp is reached. When the solenoid de-energizes, the relay closes to its normal position and the cooling fan is grounded.
If the meter fuse blew, and could not energize the solenoid in the cooling fan relay, the fan would come on in RUN.
Do your instrument cluster lights and buzzer work?

According to the shop manual, the first thing to check is the meter fuse.
1. system integrity check (shake harness and look for shorts)
2. check for shorts (disconnect cooling fan motor, relay, ECA)
3. check fan motor (check for internal short in fan motor)