Heater not working properly?

TREVJAX04

MEMBER
2004 FORD F-150
4.6L
V8
2WD
AUTOMATIC
173,000 MILES

I have the truck listed above ST, 4.6L V8. I have no hot air coming out of my vents at all. I have checked the Blender door and it's working fine. Flushed my coolant and put in new. Flushed my heater core lines and replaced my thermostat. But still have no heat. Now after I replaced the thermostat it took about 20 mins and I had a little bit if warm air come through the vents but after about 15 mins it went back to cold again, and I've not had any warm air come out since then. Any ideas of what it might be, and what I need to do to get heat in my truck? Thanks

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,289 POSTS

Hi,

Do me a favor. Start the engine and turn the heater on high. Allow the engine to reach operating temp and then turn it off. Feel both heater core hoses under the hood where they attach at the firewall.

Are both hot? Both should be. If one is hot and the other isn't, we either have air in the system or the core is still plugged.

When you flushed the heater core, did you flush it in both directions?

Note: If both heater core hoses are hot, the problem is in the inside of the vehicle. If one doesn't get hot, then as mentioned, either the coolant is low, or the core is still plugged.

When the engine is cool, reconfirm the coolant level in the radiator is full. Don't rely on the coolant reservoir level indicator. Although the manual indicates filling it via the reservoir, I have seen many situations where it didn't actually fill the system.

Take care,

Joe