Hello. I have been having some issues with heat in my truck. I have changed within the last 6 months thermostat water pump flushed the cooling system 3 times. I just recently replaced the heater core and the blend door actuator. Bled the system 3 times to be sure i got all the air bubbles out. Still ice cold air. My truck has been running for a good hour and a half temp gauge reads normal but both of the heater core hoses are still cold. Not hot at all. Does this mean my thermostat is bad?? Any help is greatly appreciated. Thank you

 

I'm not sure if a 99 has it. on my 03 there is a vacuum operated valve that stops the hot water. it's located near the turbo exhaust housing/ downpipe. I also think this valve controls the heat/ air temp; you should have a similar valve

 

I don't think earlier models had the vacuum controlled valve which is why the ball valve mod is popular.
If the hoses are cold it sounds like it's air locked, pull off a hose at the engine side and try burping it.

 

I have never heard of this. More info would be great. In the summers months the vents always have hot air trickling out of them. I always thought it was a vent door not closing all the way until the ac was switched on. Blocking the hot coolant from the heater core would be great.

mine is an e99 and no valve next to dp on fire wall. Just 2 lines that attach directly to the inlet/outlet on the firewall.

 

Serch 7.3 max cool ac mod and you should be able to find more info then you would ever need. lol it's easy mod and works well. 99 does not have it from favtory.

To original poster make sure nobody installed a ball valve on heater core lines. People do that as well sometimes to accomplish same thing.

 

@Kcroft7163 Have you checked the heater hoses themselves to see if they are clogged?

 

Oh okay, that's interesting as trucks from the 70's even have a similar valve.

I'll see if i can get a pic. I've had to replace it once because I was working on my truck and didn't realize it got pushed too close to the DP and melted a hole in it...causing defrost only. Mine came with it from the factory, but supposedly the dieselsite max cool mod is still beneficial to all 7.3's IIRC

and honestly, i do not know if it only effects ac or if it would prevent heat, but either way it doesn't sound like the 99's have them

 

I've dealt with this numerous times.



These pickups' cooling systems get airlocked very easily and will not push coolant through the heater core sometimes when the system has been drained. Get a little bit of pressure in the system either by allowing it to warm up slightly from dead cold or with a pressure tester, pinch one heater hose off and remove the other heater hose (just a little to cause a leak) at either side of the heater core....yes, those can suck. It doesn't matter which. The pressure differential will cause coolant to push through the core and once the air is forced out, coolant will flow through it again.

 

A plugged heater line will do exactly what the original poster said, no coolant will flow through the secondary circuit from the passenger side head to the heater core and back to the water pump if the heater core or its lines are blocked, but the engine will run normally and the engine coolant temp (sensor is on the water pump) will read exactly as expected. A dud thermostat would result in the engine temp reading low for a very long time if it sticks open and an overheating engine if it sticks closed.

There is no valve of any sort in the heater hose circuit on at least an early '99, just a line from the passenger side head to the heater core inlet and a line from the heater core outlet back to the water pump.

A word of warning is that those push-lock connectors Ford used on the heater hoses are a real pain in the rear to get off of the heater core tubes. The hoses are 5/8" and there is a specific tool to remove the push-connectors. The trick is in getting that tool in the notch between the flared ends of the push-connectors protruding from the end of the connector and the end of the connector. It is quite fiddly to get the tool lined up due to very little space to maneuver, also the little "fingers" on the plastic push connectors like to flex and move when the tool is placed over them.