New member here with no heat in the cab. Have been fighting this problem off and on for a couple years...it will come on for a while then disappear for months. I've had the heater core professionally backflushed, power flushed and blasted to no avail. I'm guessing someone put stop leak in the radiator at some point but when I flushed it again yesterday it ran fast and clear. I noticed my heater hoses haven't been getting very hot either which may mean something. I'd appreciate any help.

 

I think you're blendor motor in the cab needs replacing, search this or blend door, sometimes people spell it or say it different and to be honest, I forget the correct way. Another thing might be you're thermostat may be stuck open causing the heater hoses to be not as hot as they should. Can't say 100% but these may be considerations.

 

Thanks! The other thing I did notice when I checked the heater hoses is that the radiator hose was hot...quite a bit hotter than the heater hoses. Maybe this could this be a thermostat problem?? I was told getting to the blender valve or heater core was a pain is this model...is this true?

 

Yep, heater cores in the 97-laters are a PITA.

Also, despite blackflushing, a heater core can still stay clogged to a certain point to where hot coolant only circulates inside that core, but doesn't make it across the blower to warm that incoming air.

It is a 10-year old core.

Same thing with my 94 Ranger. I can backflush all I want, but that is only so much water going in to flush it that it won't really have any effect on all that scale in there.

 

Your truck is at the age when the blend door fails. You need to do some checking. 1, The motor that works the blend door is on top of the trans hump on the underside of the duct work. run the truck and turn the heat control from hot to cold. you should be able to see the motor turn (its about a 3/4 turn total). If not, you need a motor, this is tough to replace as the section of duct under it is in the way. Cut it in half just to the left of the motor. remove the screws holding it in place. Check again for operation. Next see if you can work the blend door from underneath. These doors "heat harden" until they snap and fall apart.
Checking the heater core. For this you need to get to the pipes where they come through the fire wall. To peel them off after 10 years best to cut the rubber down one side and peel away. Hook up the garden hose and run water through in both directions, this will tell you its clear.
If you need to replace the blend door or core, its not a bad job if your handy but you need a day clear. and when you do replace the blend door as it does break after 10 years or sooner. Dealer should have a repair kit.

 

Thanks for the help! I'm going to try and find the blend doors and go from there...with winter approaching, I need to get some heat back into my rig.

 

You are wasting your time on the blend door. There is no hot coolant getting to the heater core if both the heater hoses are not getting hot. Are you getting coolant flow to the heater core? With the engine at operating temperature feel the heater hose on the driver side of the core. That is the inlet side. Is it hot? Then feel the other one on the passenger side of the core. Is it hot? Disconnect the outlet hose to see if you have coolant flow. No flow would indicate a restriction in the system somewhere of a faulty water pump.

JMC

 

Though I agree with everyone on this thread, I would strongly recommend pulling the thermostat and checking it as you say the core hoses don't get very hot, but your rad. hose does. Check both top and bottom radiator hoses to make sure you have flow there. I'm not one to throw parts at a problem, but the thermostat is a relatively easy and inexpensive fix, and that sounds like what your problem is, so that's a good place to start. Not a bad idea to check your blend doors like Blue and nigel says. If I remember correctly, the doors are controled by vacuum, but I could be wrong so somebody correct me if I am. If it is vacuum, you'll have to check for vacuum leaks or even the heat/ a/c switches or the vacuum pods which open and close the doors. If all of those things check out, THEN I would say it is a heater core blockage. How does the rest of the cooling system on the truck work? Please let us know how it's going. Hope this helps.

 

There is always coolant flow to the heater core regardless of the thermostat position. So hot heater core hoses and no heat is a blend door problem. Cold/warm heater core hoses is a restriction somewhere in the system, failed water pump or stuck open thermostat. You may have had the core flushed but if there is a restriction somewhere else in the system you will not get any coolant flow to the heater core. If the water pump was failing your truck would overheat because of the insufficient coolant flow. If the thermostat was stuck open the truck would run colder but eventually the engine would heat up in stop and go traffic. So when the upper rad hose gets hot the heater core hoses should also be hot.

JMC

 

Thanks for all of your ideas and help. I'm planning on replacing the thermostat this weekend like mitch150 suggested and see if that makes any difference. I'll probably look into the blend valve after that...besides not having any heat everything else in the system seems to be functioning fine...A/C works, fan blows etc. Question: Could the core be plugged if I get good flow back and forth when I flush? There didn't seem to be any restriction of flow either way when I flushed last week. I'm about ready to get a 12volt heater for the cab and see what that will do for me!!

 

do you ever hear a vacuum sound in the cab maybe from the temp controls.

 

I've never heard a vacuum sound...I don't hear anything when I turn the temperature dial from hot to cold either.

 

The temperature control does not use vacuum. It is an electrical control for the electrically operated blend door. Only the doors that direct airflow inlet or outlet use vacuum.

The 12V heater is a waste of time. They couldn't heat a hummingbird's nest.

Replace the thermostat. If that doesn't fix it, you will still need to get proper coolant flow through the heater core as already advised before looking anywhere else.

Steve