i have a 94 ford f150 5.0 4x4 5 speed,yesterday when i left for work my heat was working fine, normally my temp gauge takes awhile to move up to normal goes a little past then drops to a steady position. when i got out of work this morning it was 6 below the first freezing morning this year started my truck up went back inside.

about 15 mins later went out to my truck temp guage was already up which was strange never goes up that quick then my heater was just blowing out cold air, i have about a 15 min ride and during that time there was no sign of heat. my temp gauge went all the way up then dropped to normal then was fluxuating the whole ride home.

the thermostat is about 6 months old, should i replace that? heater core?

about 3 months ago i had a coolant leak and fixed that, previous to this morning i had heat please help it is getting cold out and i dont have a garage to be taking things apart to find the problem thanks

 

I'd check the coolant to see if its low. If it is, your heater core could be bad. I've had them go bad without seeing puddles in or out of the truck, then one day it started blowing fog out of the vents like a fog machine.

 

Agree with above, low on cooloant will affect both irratic engine temp and poor heater output.

 

Good advice up there....the only other thing I've got is how old is your radiator cap? If you think it needs replaced it's a 13 lb cap.

 

can you lose coolant from a bad radiator cap?

 

It could, but proper function is critical to proper coolant system function.

 

I've never heard that one. But if the cap was leaking, you'd definitely notice coolant everywhere.

 

edit: with a bad cap your antifreeze will evaporate. when you have a good cap it pressurizes your coolant system and raises your boiling point so it dont evaporate.

 

oooh gotcha. that makes sense, I've never thought to replace a radiator cap.