eking81

I have had some overing heating trouble so i did the basics
new t-stat, water pump, clutch fan, hoses and a flush while i was at it i also replaced the sending unit to make sure the gauge was reading properly.

at first everything seemed fine and except the over heating but now as i pay more attention to the aux fan it seems to come on when i get around 210 and runs about 45-60 seconds then shuts off and comes back on in short runs but doesn't help hold the temp. as i looked into the problem further i found that the aux fan will come on if i turn the heater on and will continue to run if the heat is on but shuts off with the heater.

would this mean the aux fan or relay is bad? what sensor tells the aux fan to come on?

Johnthepanpire

That's what it's supposed to do.
It comes on at a certain temp and with a/c.

If it's cutting in and out spontaneously, then yes it's something electrical.

eking81

i understand it comes on at a certain temp. but if its over heating it should be running untill it gets below that temp and its not unless the blower fan is on it only runs a few seconds

what temp should it come on at ?
what tells it when its reached that temp?

djb383

Most likely it's turning on/off when the a/c compressor kicks in/out. Cycling could mean low refrigerant.

Johnthepanpire

It should come on at 220°
What actually closes the circuit and turns the fan on is the coolant temp switch.
It screws into the radiator on the drivers side facing the rear, next to the air box, about the size of a half dollar. It has a 2 or 3 wire harness coming off it.
If you have a trans cooler it's right on top or bottom of where that goes into the rad.

That could be shorting out as well.

Johnthepanpire

You could always wire a toggle switch in the cabin to the fan.
A lot of people on here have had to do that, me being one of them. It only takes like 30 mins and maybe $10 worth of parts.

I had replaced my coolant temp switch and the relay and it still wouldn't come on by itself.

You might want to hot wire the fan and make sure the motor is ok too.

djb383

On a '95 the CTS is in the t-stat cover.

Johnthepanpire

Oops, I forgot.
Can't see the year on the mobile app.
but the concept is the same how it works, yours its just easier to get to

Johnthepanpire

Wait, is that the switch or the sensor on the housing?

Edit: I'm looking in the book now and that's the sensor on the housing, not the switch. Those have two different functions, the sensor is only for the gauge, the switch its what opens and closes the fan circuit.

Disoriented Hillbilly

215ish.
Coolant temp sensor in your tstat housing.

May change that sensor and check coolant level like djb said.

eking81

the coolant temp switch is in the t-stat housing the sensor for the gauge is in the back driver side of the head

ill try changing the CTS but if the switch was bad wouldnt it cause the check engine light to come on and toss a code

rrich

The temp sensor for the gauge or light is on the head at the rear.

The sensor in the t-stat housing signals the PCM to raise the idle. The PCM closes the fan relay - the fan then runs. It should come on at about 220 degrees.

If you want it to come on at a lower temp, put a 1000 Ohm resistor across (in parallel with) the 2 wires on the t-stat sensor. Then it will come on 10-15 degrees cooler - before it's so close to overheating.

Radio Shack - 10 cents for a 1000 OHM resistor.

Or you can have the dealer reprogram it - for $150.

DFlintstone

I don't think it's that smart! (something just being "off")

Thees guys know this stuff way better than me, just wanted to add. Cycling on and off is something they can do. If it's not over heating, I wouldn't sweat it. If it's actually getting hot, and the fan isn't on, by all means change the temp switch. For the herky jerky business with the AC on, having the AC serviced will likely take care of that. (like Djb points out). I haven't figured that one out yet, but they are indeed "married" somehow.

(neat tip on the resistor Rrich, it's not so hot where I am)

eking81

ok this seems to be unclear

when the a/c or heats is on the aux fan runs all the time which is normal however is the a/c or heat is off and the blower motor isnt running the aux fan only runs in short cycles

from my under standing the aux fan should come on before over heating happens (220 degrees was pointed out) and should continue to run untill the temp drops below that temp.
am i misunderstanding this ? my temp gets well over 220 and the fan only runs in short burst and if i run the truck for an hour it will get into the red

DFlintstone

Not knowing better, I think the puter' should ignore the other signals from the AC or defrost, and run the fan when it's too hot. Changing the sensor makes sense. I might jiggle the wires while it's in the red with the fan not going....OH spit..the relay,,,I might check connections there or swap the relay...first.