ok so ive been fighting with my truck for over a year now. its a 98 extended cab 4x4 with a 3.9L engine. i just get very little or almost no heat when its cold outside.

i have flushed the cooling system twice. backflushed the heater core and it flows perfect. put in a new water pump. changed the thermostat. changed the coolant temp sensor. putting cardboard in front of the entire radiator helped a small amount but not much at all either.

the truck gets up to temp perfectly fine, just no real heat output into the cab. last night i even took the clutch fan off and that helped a little to. but i cant leave it idling to long after it gets up to temp now or it starts to get to hot.

my buddy said that he heard of someone installing a lower thermostat to work with the upper and it was a night and day difference. but i cant seem to find anything out about doing this. i would really like to though. anyone have any input on this? or any other things that could get me some more heat!

 

A cooler thermostat will put out less heat than you have now.

Putting cardboard in front of the radiator or removing the cooling fan is reducing the amount of air passing through the radiator. A correctly functioning thermostat regulates temperature controlling the amount of water flowing through the radiator.

I know you've backflushed the heater core. Feel the hoses going to the core. The inlet hose should be very hot. The outlet just a bit cooler. Neither should be warm or cold.

The blend door is cable actuated on a '98. With any luck the cable is just out of adjustment. Try this:


(1) Not applicable.
(2) Rotate the temperature control **** on the heater-A/C control so that the **** pointer is in the 12 o’clock position.
(3) Pull the temperature control **** straight out from the heater-A/C control base until the perimeter of the **** (not the **** pointer) protrudes about 6 millimeters (0.25 inch) from the face of the control base.
(4) Rotate the temperature control **** to the 1 o’clock position. Push in on the **** slightly and continue rotating the **** to its full clockwise stop. The **** pointer should be aimed at a position about 8 millimeters (0.315 inch) beyond the end of the graduated red strobe temperature control graphic on the face of the heater-A/C control base. If the **** is not pointed to the correct position, go back to Step 2 and repeat the adjustment procedure.
(5) Rotate the temperature control **** counterclockwise until the **** pointer is in the 12 o’clock position again.
(6) Push the temperature control **** straight in towards the heater-A/C control base until the perimeter of the **** (not the **** pointer) is flush with the face of the heater-A/C control base.
(7) Rotate the **** to its full clockwise stop again. The **** pointer should be aimed at the end of the graduated red strobe temperature control graphic on the face of the heater-A/C control base. If OK, go to Step 8. If not OK, go back to Step 2.
(8) Rotate the **** to its full counterclockwise stop and release the ****. If the **** springs back from the counterclockwise stop, the self-adjuster clip that secures the temperature control cable to the blend-air door lever is improperly installed.

 

i am more than aware how a cooling system works bud. both heater hoses are extremely hot, with one being slightly hotter than the other. but if its cooling off to fast (after the gauge) it would still read normal on the gauge. reducing the airflow through the radiator via the cardboard and the fan removal has both helped the temp of the air coming through my vents increase without budging at all on the actual gauge on the dash. i will for sure be trying the adjustment through for the cable.

speaking of, is it supposed to spring back a hair from the clockwise spinning? all the way over to hot? because it does do that.

 

ok, so do you have a video? pictures? because it specifically says not the pointer. but when i looked at it last night some i didnt see anything to pull out but the pointer. just not sure how im supposed to be adjusting it exactly.

 

It should not "spring back." No, I don't have a video.

After the gauge water goes to the radiator and heater.

Don't rely on the dash gauges for accurate measurements.

 

Wow...I didn't go through all that when my 98 started losing heat effectiveness. I did the cable thing and mine seems fine. Mine eventually gets hot as the truck runs more and more. I need very little heat as I have moved to a warmer climate however, it's still good to have for chilly mornings. I'm think this was a gradual thing as many years ago it was fine. Must be the nature of this truck, my wife complains all the time it doesn't get hot enough so with that I tell her "Drive your fancy car and leave my truck be". Anyway, interesting that this is a common problem.

 

If the heater hoses are very hot to the touch, then the heater core is getting the hot coolant. The problem must be inside the dash somewhere. A vent or door not opening. I doubt anything done in the engine bay will make much difference.

 

yeah, im thinking the same thing myself to. and i had my buddy help me look at that little procedure for adjusting the cable with the **** and neither one of us can figure out even remotely what we are supposed to be doing. i pulled the gauge bezel off and pulled the heater controls out and even the front off the heater controls and see nothing else you can turn. my buddy called his friend at the dodge dealership though. he said to pull the glove box out and i should be able to reach the recirculation door. he said unhook the cable and move it manually. if it has an effect then its just the cable that needs adjusted for the blend door. if not then the blend door itself inside of the box is probably broken.

 

The blend door is vacuum operated so im sure its not opening the whole way.

 

No. The blend door is cable operated.

The mode doors are vacuum operated.