96 s10 heat not working

My girlfriend has a 96 s10 4.3. The heat is COLD. The engine is heating up to normal operating temp, so it's not a thermostat or anything like that. Problem is, the heat is ice cold. I really don't think the heater core is bad, because I think when they fail, they burst, not plug up. My guess is, the temperature selector on the dash is messed up. Maybe a broken or pinched air line? Anyone have any ideas? Winter is coming fast and my girlfriend is cold. Thanks.

Well, don't count anything out until you know for sure. Assumptions are the mother of all automotive repair fuckups. ;)

Two things can be wrong, the door for the air to go through the heater core is stuck or broken or the heater core is plugged.

Take your rad cap off when cold and tell me if it looks all gunked up.

Did you mix green with the orange coolant by chance?

No, I didn't mix antifreeze. I never heard of heater cores plugging until I looked into it on the internet. Sounds like the orange antifreeze is far more likely. If I find that the heater core IS plugged, maybe I should flush the radiator and block as well. Tonight I will get it up to operating temp and feel how hot the 2 heater core lines are. If they are both hot, I will move on to flappers. Thanks.

I had this problem after getting new intake gaskets on.What the problem was on mine was the heater core was air locked.I took off the heater hoses and stuck a garden hose on one and turned the hose on.Ran it till just water came out.Hooked it back up and no more air lock.

time to reverse flush your cooling system and add new dexcool coolant with a new rad cap.

O.k., Warmed up the truck. Felt the radiator hose, hot. Felt the heater core, ice cold. Time to start ripping out the core. I already bought the new one.

try flushing it first.

Only change a heater core if it is leaking.

Reverse acid flush it before you doing anything.

Just curious, did you check your coolant level. Out of all your troubleshooting you never mentioned that you did. Maybe you did but I'd hate to see you go to all this work just because you coolant level was low.

Just curious, did you check your coolant level. Out of all your troubleshooting you never mentioned that you did. Maybe you did but I'd hate to see you go to all this work just because you coolant level was low.

You got a point there, check the overflow bottle and remove the rad cap and check the coolant level when the engine is cold.

If the bottle is up to level and the rad is not right up to the top, replace your rad cap.

did you check the heater valve? there should be a valve connected inline with the heater core lines. some are vacuum actuated, newer ones are solenoid activated. make sure this valve is opening. check to see if the vacuum diaphram in the valve is good or the solenoid is activating (which ever one you have). good luck!

O.k. Blew out with 10 psi of compressed air. Heat is hot now. Thanks to everyone. I think it's still like 90% clogged, whenever I step on the gas I can hear a whooshy-bubbly sound from the core. It'll prolly clog again. I will do a total flush on the whole system and it should help. Thanks again.

Stop doing a half ass job, reverse flush the system, install a new rad cap and finish the job properly.

Stop doing a half ass job, reverse flush the system, install a new rad cap and finish the job properly.
"I will do a total flush on the whole system "

D'oh, my bad.