82 C10 runs cold

[y2k_harley]

I have a problem, my 82 C10 with a 250 straight 6 engine runs cold.  Earlier I made a trip of around 25 miles and the temp gauge never got off cold (bottom line on gauge) and the heater made very little heat.  I figured it had to be the thermostat, so replaced it with a new 195 degree.  It still runs at about the first line above the bottom.  Heater blows about the same temp as blowing on your hand.  I have covered the entire grill area this morning and still wont raise the temp gauge on a 5 mile trip.   The heater hoses are warm (not hot), the top radiator hose is a bit warmer and the bottom radiator hose is cool.  The coolant level in the radiator is within about an inch of the top neck.  Any ideas???

[paniolo]

Your water pump working?

[Irish_Alley]

did you test your old thermostat?

[bake74]

     The next step, ( since you changed the thermostat, and check the temp of the hoses ), would be to do a system flush and make sure there is no clogs, especially in the heater core.

[y2k_harley]

Your water pump working?

Not sure,  after driving that far I was able to take the cap off the radiator.  There wasn't any movement in the coolant.  After replacing the thermostat it squeeled for just a few moments and then was quiet again.  Could be the problem.

[y2k_harley]

did you test your old thermostat?

Nope, just chucked it.  Figured it was bad.

[Irish_Alley]

im stumped and just throwing ideal out there lol. i mean if the pump was bad it would be overheating if the thermostat was bad it would be overheating. if the core was bad or clogged it wouldnt heat up. if the water temp doesnt get hot it wouldnt work. if the thermostat was a fail safe or was stuck open then it wouldnt let the water heat up to 160+. since you verified both lines to the core are the same temp but warm then its flow is even. the only thing i can think of is your temp sensor is bad your water pump is bad and your thermostat is bad and all three going bad at or around the same time i dont see possible but who knows

[Lt.Del]

A t-stadt could be bad when it sticks open, not allowing the engine to warm up.  Are you sure you put the new t-stadt in right side up?  Spring side down into the intake.

when the old t-stadt came off, it should've been closed because, let's say it is only 60 degrees outside or so---so it should be closed.   I would look at that to see if it is stuck open, thus not allowing the engine to heat up correctly.

if that checks out ok, i would say your coolant system is not under pressure.  Maybe your radiator cap needs replacing or something.

[firefightin1]

sounds like a pressure issue to me, I would have the rad cap test or replace it.  If the same problem exists then i would say it could be a clog in the block its self.  not likely tho also might try a hotter t stat,  I would also check the clutch on the fan..... This is most likely your issue, if it is running a full pull at idle then its not allow the temp to rise.  JMO

[bd]

...if the pump was bad it would be overheating, if the thermostat was bad it would be overheating, if the core was bad or clogged it wouldnt heat up. if the water temp doesnt get hot it wouldnt work. if the thermostat was a fail safe or was stuck open then it wouldnt let the water heat up to 160+. since you verified both lines to the core are the same temp but warm then its flow is even...

Irish makes valid points.  Except for a t-stat hanging open and excessive air flow through the radiator, most of the suggestions thus far would lead to overheating.  It's been many years since I've seen a 250 L6 & can't quite recall if there is something unique about the 250's cooling system configuration, but the symptoms are familiar.  I don't recall if the heater circuit is engineered as a t-stat bypass on the 250, or if there are coolant restrictions engineered into the head gasket.  If an engineered restriction has been removed from the cooling system (which includes the heater circuit), sufficient coolant could be bypassing the t-stat to effectively mimic a t-stat hanging open.

Are the symptoms new for your truck or has it always been cold blooded?  Did changing the t-stat help at all?  How clean is your cooling system?  Have any other seemingly insignificant changes been made to the cooling system?  For instance, have any heater hose fittings been replaced, heater valve bypassed, hoses rerouted, head gasket replaced, etc?  Seems like we are missing something simple.

[Jason S]

Just some ideas here:

Pull the thermostat back out (or get another thermostat) and drop it in a pan of boiling water to verify that it is opening. Remove the thermostat and let it cool to ensure it closes correctly.  If it is working correctly, reinstall and remove the radiator cap. Then start the truck and let it idle until warm/hot to purge air out of the system. Fill radiator with antifreeze mixture as necessary then replace radiator cap.

The other possibility may be that the fan clutch is seized and pulling air when it shouldn't.

[y2k_harley]

Ok, finally got a chance to look at the truck.  First I checked the coolant level,  was about 4 or 5 inches down.  Noticed the lower outlet to the radiator was wet.  Checked the hose clamps (all of them) and were somewhat loose.  Topped off the radiator and started it up.  After a few seconds there was coolant seeping down the hose.  Closer look and I see a pinhole near the water pump outlet.  OK that would explain the lack of pressure.  I figure that if I have to drain the radiator I might as well change the upper hose and heater hoses.  I thought the water pump made some noise when I changed thermostat so I might as well change it out.  Had to special order the water pump and both radiator hoses, go figure.  Got everything back together and fired it up,  Crap the pulley was rubbing on the waterpump housing.  The belts also looked like the pulley needed spaced out.  Not sure what is going on there, but they ordered another pump.  I just spaced the pulley out for now with washers (3 each bolt) and every thing seems lined up.  Fire it up again and let it sit there running for a few minutes, the gauge was up to the first mark.  Took it out for a quick ride (about 4 miles) and the temp gauge stayed at the first mark (1/4 up the scale).  The heater seems like it is pretty warm.  Heater hoses and upper radiator hose are much warmer than before.  I guess time will tell.  If nothing else, I did some much needed maintenance on the old girl.   

I also change ALL the rotting vaccumm lines on the engine.  It would always sputter and miss  pretty hard when you first started it until it would warm  up.  That all went away with the new lines.  It was a pain in the butt, but was definately worth it.

[firefightin1]

I would say you need to replace the fan clutch..... it should be running at 200 degrees min. ^{this can cause your issuse,  also sounds like they order u a short pump instead of the long one there is about a 1/2 inch difffernets}

[1979C20]

Timing and/or air-fuel mixture can make a truck run cold. My brothers 76, the temp gauge never moved past the coldest temp (130) until I afdusted his car and timing. The carb was lean, to the point that the mixture screws were all the way in and I dont know how it was running with no fuel.  And the timing was really far retarded.

[Irish_Alley]

79 i thought those screws where for air mixture? But the timing can play a part in temp but idk about keeping the engine too cool. If im not mistaken and I can be but the leaner them air/fuel mixture the hotter it gets. the fan clutch works when its gets hot, if this what the case flex fans wouldnt let a engine get to operating temp.