I have a 1994 Ford F-150(351) that is showing low coolant temp. I replaced the thermostat twice due to the truck not warming very fast and not giving much heat in the winter time. Now the truck shows low temp on the gauge. Also, you can see on the gauge when the thermostat kicks in due to the gauge moving during different operations of vehicle speed. The gauge reads NORMAL it is not an actual temp gauge. It used to read around the R to M mark and now shows near the N to O. I have checked the gauge and it is operating. Any help???

 

Your coolant might literally be low. If there is not enough in there to reach the coolant temp sensor then it will not read or read normal. Sometimes when you do a coolant flush service the cooling system you can get an air pocket.

Does it sound like there is water rushing through some pipe under your dash inside the cab?

Try running your heater for a good while to see if it will catch the air pocket. If this doesnt work, try squeezing the hose that leads to/comes from the thermostat.

You could also drain the system again (dont forget to remove the radiator cap)
and refill. There are things that I could tell you to do or not do that have the opposite effect for others and they will tell you as such, its kind of a crap shoot with air pockets. There are some that will tell you that there is a sure fire way to never get air pockets but I'm sure they have or will one day have to remove an air pocket using their method.

THese are all the cheapest methods I can think of to try and solve your problem. Next would be to replace the coolant temp sensor. Which if I'm not mistaken is also cheap if you just buy it and do it yourself. Should be between 5-15 bucks for the part.

Good luck keep us posted.

 

Your coolant might literally be low. If there is not enough in there to reach the coolant temp sensor then it will not read or read normal. Sometimes when you do a coolant flush service the cooling system you can get an air pocket.

Does it sound like there is water rushing through some pipe under your dash inside the cab?

Try running your heater for a good while to see if it will catch the air pocket. If this doesnt work, try squeezing the hose that leads to/comes from the thermostat.

You could also drain the system again (dont forget to remove the radiator cap)
and refill. There are things that I could tell you to do or not do that have the opposite effect for others and they will tell you as such, its kind of a crap shoot with air pockets. There are some that will tell you that there is a sure fire way to never get air pockets but I'm sure they have or will one day have to remove an air pocket using their method.

THese are all the cheapest methods I can think of to try and solve your problem. Next would be to replace the coolant temp sensor. Which if I'm not mistaken is also cheap if you just buy it and do it yourself. Should be between 5-15 bucks for the part.

Good luck keep us posted.

 

Make sure your temp indicator isn't giving bad readings. disconnect the lead from the sending unit and ground it. It only has one wire going to it. Have someone watch the indicator while its grounded with engine off, key on. If it sweeps to hot it's O.k.. If not the sending unit is TU. Be careful, it happens fast. Don't keep it grounded for to long or damage to indicator will occur.

 

Thanks for the response. I have checked the temp indicator and sending unit. Both show O.K. I also have checked the coolant level, and squeezed the radiator hose. I do not hear the sound of water under the dash. What is this a sign of? I also have not flushed the system. I did not think I needed to when I seen that the coolant is flowing, and the upper radiator hose is hot. Let me know.

 

if you hear the sound of water under the dash either your heater is or is about to crap out or you have an air pocket in your coolant lines

if everything checks out i dont know what to tell ya man. hopefully someone will come on with more knowledge on the subject.
good luck

 

start with a cold engine
take off the rad. cap and insert a thermometer
that goes to at least 220
start engine and let idle until the thermostat cycles
2 or 3 times and the system is at full operating temp
this gives a base line for the dash gauge
it will also tell if the themostat is operating properly
dash gauges are very fickle and any work done on
the system can change the base line of the gauge

 

Did you use a Ford t-stat? What temp on the t-stat? I've found I get differences in the gauge with off brand t-stats. I then replaced with a stock temp Ford t-stat and the gauge went steady again.

 

Could a locked up clutch fan cause it run too cool?

 

Thanks for the responses. I will check my engine temp with a thermometer. Will it read when warm what the thermostat is rated for? I purchased an aftermarket thermostat rated at 195 degrees. I tried to buy a hotter thermostat in order to make the truck heat better. I don't believe that my clutch fan is locked up, but how would I check to make sure??

 

If your fan clutch was locked up, you wouldnt be able to turn the fan without turning the engine. A good fan clutch will let you spin the fan without turning the engine, but the fan should only turn about 1/5 the way around (the next fan blade should end up where the one in front of it started).

 

was that a serious question? how could a locked up fan clutch i.e. fan is not spinning cause a "too cool" symptom"?! It would have the opposite effect. If the fan is not moving cooler air then the engine runs hot.

Replace your coolant temp sensor. It costs like 5-20 bucks. Cheap insurance even if it is good which it probably isnt.

UNLESS, you have low coolant which I already think you said you didn't.
If you do, you may have a tiny leak somewhere in the back that doesnt leave a puddle because it burns off once it hits a hot engine part like a header or whatever.

 

Very serious. Like locked up Tourqe Converter. Non free spinning.

 

if a fan clutch is locked up, then the fan turns ALL the time If the truck is running, if the truck is off, then the fan WONT move. the fan clutch on my 87 f150 4x4 is locked up, so it pulls at the speed of the motor

 

Also if the fan clutch is locked up you're truck will sound like an airplane when you rev the motor.