I cant get my heater to keep blowing warm. I had to change the heater core a couple months ago after it started leaking and now it wont blow warm air. I think it keeps getting air locked but the coolant seems to flow in and out fine. Coolants topped off. Every time I unhook a hose and hook it back up it will blow warm but then say I shut it off overnight the next day it wont get warm. How can I make sure there is not air in the system? Its getting frustrating, now being under 30 degrees outside im starting to care about heat.

I have tried to two different heater cores, changed the thermostat, made sure the vent is in the right direction.

 

what t-stat did you put in??ford or international only. parts store stats don't work in our engines.
secondly, do you have the heater hoses hooked up correctly? if you have the inlet hooked to the upper side of the core, it will not fill properly, leaving air pockets. the inlet goes to the outside fitting, and the outlet is the inner fitting(outlet hose goes to the water pump.)

 

I went thru 3 advance heater cores that would leak before buying one from NAPA that didn't leak. I tried 2 Store brand thermostats and after being told "FORD OR INTERNATIONAL ONLY" went with Ford. No more problems. Also replaced the heater gage as the original Ford gage was worthless for trying to figure out the temperature. The guys on this forum know what their talking about

 

Guess ill be putting in a new thermostat.... What exactly is the problem with part store ones? The truck warms up and runs at a good temp. I tried switching the heater hoses a few times with no difference with my issue, good to know that you can hook them up wrong.

 

Is there another routing that shows a 'tee' in a heater line? One of the trucks blew a heater hose, and just getting ready to replace it the other day when I discovered this tee in the line. It looked like it heads towards the radiator, but didn't follow up as it was dark and I didn't have a decent light. Is that a bypass hose around the thermostat to start giving heat faster?

 

Yes, mine has a tee in the line, tee goes to fitting in bottom of radiator, other ends go to the block and the heater core... I believe this "teed" line is on trucks with an auto trans...

 

Yep, this is one of the trucks with the E40D in it. I should look to see if the dually with the C6 has it.... also have a truck here right now with a ZF5 in I should peek at.....

It's nice having 4-5-6 trucks here to compare to each other sometimes!! LOL

 

On the pic figure 21 above I put a Prestone T fitting with a removable cap in the outlet to water pump hose, I use it to bleed air from the heater hose. I just lift the hose engine running and gently open the cap......air out.... close cap securely

 

Put in a thermostat from the dealer last night and still no heat, when I took it apart I found that that small hole in the thermostat housing was siliconed shut. Is that for bleeding air out of the system? I thought for sure after cleaning that up and putting in the motorcraft thermostat that my problem would be solved but no luck..... Any ideas?????????

 

Just thought I would add something to this thread I found out today while swapping heater hoses on one of the trucks. It turns out, on this truck at least, that the 'Tee' going to the bottom of the rad has 1/2" hose, not 5/8" like the rest of it. Of course I figure that out AFTER I have it all apart etc, so now I have to drop it midstream until I get some 1/2" hose. At least I got the rest of it swapped out when we are having a mild spell here.