CLDardeniii

Hi - I have a 2002 F-150 XLT, 4.6L V6, 2WD The heater has not been working. I have replaced the thermostat, replaced the heater core and flushed everything, ensured it is full of coolant, replaced the intake heater hose, and checked the blend door and actuator. All those are working properly. Both heater hoses are getting hot but it takes several minutes before they do. Still no heat. Occasionally the heat will kick in for a about 30 - 45 seconds but this does not occur that often.

The truck never overheats unless the coolant gets low (hence replacing the intake heater hose - it was leaking after replacing the heater core so I had to replace it). I am stumped as to what it could be.

The AC works great and all the temperature switches blow at the speeds I set them on. When turning from cold to heat, I hear the blend door moving and have verified it is working.

Could there be a water pump failure that would cause not enough flow to the heater core but still not cause the truck to overheat? Or is there some electrical connections I can test?

Thanks to anyone who has some insight as it is getting cold here in VA and I am getting tired of driving to work freezing my pants off

Martian

Well if you did all that, there's not much reason why it WOULDN'T be working... you said the hoses get hot but it takes a few minutes. A few minutes starting from when? From cold start?

Is airflow ever impeded or is it JUST temperature? Your next step might very well be the water pump. Shouldn't be too hard to replace, you've already done everything else. And since you did everything else... why didn't you just replace that as well?

If it were me, I'd take that blend door apart and look for any signs of impaired movement. Yeah, you can year it, but that doesn't mean it's actually moving all the way. Not sure why you'd get heat for a few seconds and then it stops, though.

CLDardeniii

Thanks for such a fast reply! The heater hoses take several minutes to warm up from cold starting. I waited until the temp got to normal operating temp then a couple minutes after that I could tell they were getting hot. As for the water pump, I didn't change it because I was never overheating and figured it was working just fine. Not many water pumps I have had experience with have gone bad without leaking from the weep hole or causing overheating. I pulled the entire dash apart to replace the heater core and have verified that the blend door is not impeded at all. I even manually opened and closed it while running the heat to verify. Also the airflow is never impeded.

Martian

That's normal. Your engine gets hot, then your thermostat opens after you get to operating temperature. The hoses don't warm up until the thermostat opens and coolant starts flowing. I'd definitely replace that water pump. If it's never been done before, it wouldn't be a bad idea anyway, so might as well.

Martian

Also, did you get eyes on the actual blend door itself, inside the duct? You may want to price one out and replace that module, too. Sometimes the motor breaks off from the actuator, so it looks like something's going on in there because the actuator is moving but the door isn't.

CLDardeniii

Ok so I just drove for over 40 minutes and then checked the heater hoses for temp again. Both are cold.

As for the blend door I have completely checked it and it is not broken and is closing tightly.

Martian

Yeah, make sure your thermostat you bought is for the right temperature and replace the water pump.

GhostriderI

Have you checked the vacuum shutoff valve in the heater line? It could also be acting up and not opening to let water flow. ie: cold hoses/no heat

CLDardeniii

I havent. Didnt even know that existed. I will have to do a search to find where it is then check it. Thanks!

Martian

Wait, so the heater hoses are cold. Are the regular radiator hoses hot?