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LSC9901 · 03-07-2012, 05:31 PM

Just discovered that the fan runs constantly. Has anyone else had this problem and if so what was your cure ? Or at least some thoughts on where to look. As a side note the temp gauge shows that the temp is cold all the time. We just came back from a 285 mile journey and temp never moved.

Chevy 454

Tha_Rooster · 03-07-2012, 06:39 PM

I believe the fan turns all the time and engages more when the engine gets warmer then slows down. If it stays fully engaged you may need a new clutch.

BonesBarth · 03-07-2012, 06:55 PM

Yep, the fan turns all the time. I'm assuming you have a mechanical fan with a thermostat clutch, not electric. When I start up mine when it's cold, I can hear the fan get loud for a few seconds. Sounds kind of like a jet. As the engine heats up, the fan clutch limits the slip of the fan to draw more air through the radiator.

When the engine is OFF, give the fan a push. It will spin on the fan clutch.

Oh yeah, there is also the mech. fan that change their blade pitch at higher RPMs. I don't know what they call this type of fan but someone here will. They don't use the clutch but if you have this (I doubt you do), it isn't factory.

timex · 03-07-2012, 07:31 PM

When the engine is off and cool try to turn the fan blade by hand ,you should feel some resistance but it should rotate unless the fan clutch is bad .They make two styles of fan clutches. One is temp controlled and has a coil wound spring on the front of the clutch and the other runs all the time. You want a temp controlled one if you have to replace it. They will be loud when you first start it then quiet down till the engine is warm enough to need more cooling.

LSC9901 · 03-08-2012, 08:18 AM

As usual I have explained the problem incorrectly. It’s the electric fan in front of the radiator not the belt driven fan on the water pump shaft.

BonesBarth · 03-08-2012, 10:00 AM

There is a temp sensor in the cooling system. It's just a switch that closes when the coolant gets hot enough. That switch could be stuck closed keeping the fan on.

Follow the wires from the fan. They will probably lead to a relay which will be connected to the temp switch.

edgray · 03-08-2012, 11:58 AM

Quote:

Originally Posted by LSC9901

As usual I have explained the problem incorrectly. It’s the electric fan in front of the radiator not the belt driven fan on the water pump shaft.

Not sure if true on your Chevy P32, but the later model year Workhorse chassis were wired to turn on the electric fan(s) whenever the chassis A/C was "on" in either cooling or defrost mode.

LSC9901 · 03-08-2012, 12:03 PM

Quote:

Originally Posted by edgray

Not sure if true on your Chevy P32, but the later model year Workhorse chassis were wired to turn on the electric fan(s) whenever the chassis A/C was "on" in either cooling or defrost mode.

We did double check that and it runs with the AC on or off.

born2camp · 03-08-2012, 02:56 PM

Maybe previous owner wired in a switch to turn them on/off at will and it is in the on position? Trace the wiring to be sure, at least that way you will find the sensor also.

farmallbob · 03-09-2012, 07:34 AM

there are two sensors for temperature. One is located on the head on the drivers side. This one provides the signal to the temp guage. The other one is at the front of the engine at the thermostat housing. This one controls the electric fan.

LSC9901 · 03-09-2012, 10:34 AM

Does anyone have a documented source where wiring diagrams for the P30 chassis can be had via the internet?

Thanks so far for all the directions towards the sensors. We believe that is where the issue lies but we do want to make sure the wiring hasn't been messed with. We have already found one wiring change but it shouldn't have any effect on this problem.