i've been searching for about a hour on this, cant find a good solid answer really. 94 ranger auto 3.0L. Since its gotten cold out i have no heat. It gets warmer as i drive but not nearly as hott as it should, i mainly just leave it on defrost so i dont have to feel the air blow on me cause its to cold. The tempeture gauge will goto normal and at random times go up to hott, then shoot way back down to normal. And it will do this numerous times while driving. Now i opended that valve near the blower box, the line running to the heater core with the T-fitting, and i cranked the motor over and fluid came out. I dont know which way the fluid runs threw but is this the out or in line? Also the heater control valve i've seen people talk about, is there a way to test this? i know exactly where its located just dont know much about it. And lastly could my t-stat be closed shut, and once it gets so hott it opens and thats when the temp. drops? thanks for the help guys

 

the radiator is also full of fluid to

 

sounds like 2 things

you either have a plugged heater core
( just reverse flush it ,, or it is plain rusted out on the core )

or you have a cylinder head leak ,, check your engine oil

 

just checked my oil and it looks just fine. I have no leaks anywhere either

 

find where the coolant pipe exits from the rear of the cylinder head to the firewall
( that is your heater core inlet pipe )

remove both hoses ( remember where they went )
and use a pressure sprayer ( very carefully ) use 1 second bursts of high presssure water
until all of the gunk has finished being flushed out.

do not be surprised if you heater core ruptures .
( i recommend that you just replace the heater core anyway )
it is probably past it`s prime,, and the fin material has probably all rusted away leaving mostly the coolant tubes left

 

alright, i pulled off the hose that comes out of the heatercore, the outgoing side of the core. Absolutely no fluid came out. Should fluid have came outta that ? also could i use air instead of a pressure washer?

 

think we rulled out its the thromostat. i had a buddy come over and i watched the gauge as it rose up to hott, the radiator wasnot hott at all. Once the gauge started going down he felt the change in the upper hose when the thermostat popped, so im going to buy a thermostat in a few. Both of the heater hoses were hot also.

 

if no coolant came out ,, then the core is plugged up
NO! you must use water under pressure to dis-lodge any debris built up inside there

but i would recommend to just replace that heater core ,, it is way past its prime

they usually do not last more than 8 years in the snow belt ( especially areas that use road salt )

 

I agree to flush out the heater core, but I don't usually do it with a pressure washer. I just use a garden hose and flush it back and forth to help dislodge any debris. I would absolutely try this before removing or replacing your heater core. They can be quite a pain to remove.

Also the way you describe the heat to continue raising and lowering sounds like the thermostat keep opening and closing, which might not help the motor warm up properly.

 

i forgot to mention, right when i undid that hose to the heater core, nothing came out. but when i squeeze the going in side it came out the other side. I just got done replacing the thermostat and i have great heat now. Both lines to the heater core are hott also.

 

i suspect you installed a FAIL-SAFE thermostat in that engine

if not ,, you are darn lucky that thermostat was not seized in the closed position