This next statement is from someone else and not from me but it makes sense to me........................Here it is....................Even with minimal flow the two heater hoses will get hot and you can’t really gauge the heat in the core by feeling the two hoses on a hot engine. What you have to do is put the heat/fan on full blast and feel the two hoses from a cold start. The hoses should warm up at the same rate and get uncomfortably hot in a few minutes.

 

The only problem I see here is "a few minutes".... The hoses won't get "uncomfortably hot" until the water inside them is hot enough to do so.... "A few minutes" Is subjective to the current environment. If you're in Wyoming it's 10 degrees out, it's going to take a lot longer for that water to heat up to that level than if you're in south Texas where it was 78 degrees today. So to add to that statement to clarify The hoses should warm up at the same rate as the engine warms up and get uncomfortably hot a few minutes after the engine reaches operating temperature.

Also, there is no heater control valve in the 02 150.... The water is always flowing through the core whether the heat is on or not and whether the fan is on or not. The heat is separated from the AC by the blend door.

The fix? Unless it's that blend door not opening and As long as the heater core isn't leaking...
Disconnect hose hoses at the block (or cut and install a backflush kit on the outlet line, and only disconnect the inlet from the block), backflush (push water in the outlet hose) it till it runs clear with very low-pressure water,
Then use real low pressure (5-8 psi) from a compressor to blow it dry. Fill the heater core with straight CLR, let it sit for an hour.... Rinse and repeat. 3 times should do it.
Then hook the hoses back up to the engine and enjoy warm air...

Make sure you are disconnected from the block... I dont know that CLR and Antifreeze make good bedfellows. If you go the backflush kit route on the outlet side, make sure to pick up an extra female hose bib to barb adapter... Holding the water in that backflush tee is a PITA....
It's a hell of a lot faster, easier, and cheaper than paying a shop 10 hours of labor to replace the core (that is the book time for a heater core in this truck).... if it's leaking or if it's that blend door I previously mentioned.... then you've got no choice but to pull the dash, disable the airbags and drop the steering column.... at which point you might as well replace the heater core while you're there also

 

If that's what you were led to believe, good luck and wear your long johns.You don't even know if your engine is running at its proper operating temperature.

 

Block and radiator flushed 6 times before the new heater core was installed , so here's what we have done to it so far.....New Water Pump, New Thermostat, New Heater Core, New Blend Door, Heat was good after heater core was replaced, drove the truck a few times and had fairly good heat, today drove about 10 miles and the heat was good to start with then it went to only luke warm again, drove another 25 miles and went inside for a doctors appointment for about 45 mins. came back out and had good heat again but it gradually cooled down some on the way home...Getting very upset with this truck and the heater problem, any advise is appreciated, don't know what to do next with all this work being done and still having a heater problem. after driving it and the truck warms up but heat gradually got worse, then go inside with truck off for 45 mins then heater works better again. why does it build up heat when sitting with the engine off after it once gets up to operating temperature. Thanks in Advance.

 

New thermostat, new heater core, new water pump... What led to changing all of those? If you're just firing the parts cannon at the heater, your next part is the heads, maybe the block. I'm not being facetious. What you have is a flow blockage somewhere in the coolant tubes... best guess would be it where someone improperly ran a block sealer through it to stop a leak and didn't flush it well enough after. That **** breaks loose and plugs a heater core in seconds. That's why I said to disconnect the core for the block and flush just the core.
Then tie the heater hoses together and flush just the block (disconnected from the Radiator with the thermostat pulled.)
Then flush the radiator.
Make sure you are BACKFLUSHING all the way through... pushing water in through the radiator is useless.
Connect everything back up, dump in some radiator flush, drive 100miles over a three day period, and do it again.

If you get no improvement there, you are at a plugged block. Thats really not worth messing with just to get the heater working.

 

Had the Thermostat and coolant flush done last year, helped heat some. this year had luke warm heat, had heater core flushed two different times, it helped some but luke warm heat again. read about water pump could cause this so might as well try that first, so new water pump, thermostat and heater core flush all done by a mechanic....good heat for awhile then back to luke warm heat again. so might as well have the heater core replaced, found someone to do that, he replaced the heater core and blend door (and I had him replace the inlet heater core hose that has the restrictor) and he said he flushed the cooling system 6 times with the heater core disconnected, we weren't there to watch him. this is my Son's truck and he does not have a garage, too cold here. I guess we need to find a Mechanic to do the flushing of the block with the thermostat out like you said.

 

Reply in Post #16, Thanks