I posted a message a few weeks ago asking for information about what would make my '94 F-150 5.0 overcool. It will warm up fine at idle, but as soon as I get up to speed (55mph ), it will drop to the cold mark and the heater goes cold. The response was check the fan clutch, maybe it was engaged at all times. I don't have one, at least not an electrical one. Is there a mechanical one? Does anyone have any other suggestions or information. It is definately not the thermostat (I put the fourth one in last week) and the guage is working properly. I just don't get the heat! Even though I bought the truck new, is it possible to have too large a radiator? I don't know what else to think. Any responses appreciated.

 

I'll take a stab at this...never heard of over cooling except on some of the larger diesel trucks. You've seen them going down the highway with a radiator cover that closes off some of the radiator especially during the winter...you could do the same. Yes there are mechanical fan clutches
they are attached right to the fan, about 7 or 8 inches in diameter, flat on the fan side and kind of a tapered shape with 1/8 inch thick aluminum fins on the water pump snout side. They are designed to slip at higher RPMs and at cold temperatures I believe. A question...you said you've had the truck since new...has the problem always been there? If so maybe Ford did slip in an oversize radiator. You have a couple other options
1. Change out your fan blade for a smaller less efficient size. 2. Replace your mechanical fan for a thermostatic controlled electric fan. 3. Cover part of your radiator. 4. Remove the fan shroud (it makes a less efficent radiator since the air can now go around instead of thru the radiator). Hope this helps. Deen

 

Yeah, I had an old Studebaker that didn't get hot enough to heat in the winter and put cardboard in front of the radiator. Usually that's more of an indication of poor circulation somewhere. Are you sure it's running too cool? Check the heater hoses and see if they are hot. It could be a flapper in your heater ducts that is not opening properly. My truck kicks out good heat with the temp gauge just starting to come off of cold. It doesn't take a lot to start kicking warm air out and by the time my temp runs normal, I could heat you out of the cab.

Good luck,

Slik

By the way, a cool running engine runs more efficiently.

 

First of all check your sending unit, it sends signal to your temperature gauge, it is very simple test. Disconnect the wire to sending unit
and ground it to chasis ground, turn the key to
on without turning motor on, your gauge should now
read maximun temperature, if it does then your
sending unit is probably bad. If the gauge does not go to max. temp. then check for a bad or broken wire. By the way sending unit is a sensor
that is found on motor block with a green to dark
green wire running to it.
Next: If your sending unit is not at fault and the
gauge is okay..,then refill your radiator..,but
this time you must have truck and heater on. This
will allow for the correct water level of motor,
heater core, and radiator. You should probably do
this before performing gauge test.
One more thing, warm up your truck, turn on heater, have some one run the truck up to a high rpm and watch for water hoses to the heater core collapsing, it could be that the hose is collapsing at a high rpm.
Good luck,
EBTE tech