have a 1998ram 1500, getting terrible heat out of it, I replaced thermostat thinking that was issue. the water at the heater core itself if hot from both outlets, I tried bleeding air from system, doesnt seem to be the issue. I have noticed that if your rev truck to 2500 rpm the heat starts to flow but as soon as you release to idle returns to cold. LOST HERE any help greatly appreciated!!!!!!
Thanks tvindivo

 

wish i could help but my 98 1500 is also having heat issues. Only with mine, it blows hot air for about 5 seconds or less then blows ice cold no matter what mode i select.

 

vent control cable or vacuum lines have broekn/ rotted or the cables became disconnected somehow.


last resort is heater core plugged to no end

 

it sounds like at low rpm your water pump is not pushing eough hot water through the heater core.
have you backflushed your heater core yet ? if not, try that.
also, make sure cooling system is completely full and overflow tank at max. any air in the system will rise to the highest point, which tends to be at the heater core. it might take several fills to purge all the air. any sloshing or gurgling sound is also an indicator of air bubble.

 

if my heater core was plugged i wouldnt feel the heat at bothports thought correct??? I remove the dash covers yesterday to test the vacuum lines and verify the cable is good. I did notice that when you move the control from cold to hot, you get hot air for like 20 sec and then it goes cold again, could this be possible that the flap is damaged or not sealing correctly. I am going to get me another thermostat today and try that.The other thing is the water temp at rad is cold, I can run my for an hour and remove the rad cap the water is not very warm at all, but yet the heater hoses going to the core are, is it possible for the rad to cool the water that fast, Idid test the water in the rad with an infared tester only to find the temp at 82 degress, awfull fricken chilly. which makes me want to believe it is the pump not circulating the water correctly.All I know is thing is starting to give me a head ache.LOL
Once again all help is greatly appreciated. Thanks tvindivo

 

i just noticed your post about the water sloshing or gurgling, i did notice that when you remove the rad cap there seems to be no flow fo the water, however when yourev it up the level drops and sloshing/gurgling is present, is this just the water pump pushing water thru the system or is it possibly an air lock, the bubbling is not present all the time just from time to time it appears as you rev the engine.
Totally lost
tvindivo

 

heater core broke replaced it, raditor cracked replaced it, replaced the thermostat, flushed raditor, still have ****ty fu....en heat!!!!!!

 

Your heater core has pinholes in it. I bet it looks like this:


That's mine before I changed it. That thing would barely heat the truck and I was always losing coolant. Now, I barely have the heat on and it roasts me.

 

I havent noticed coolantlose at all though. Plugged possibly, Does the water ciculate thru the heater core and back to the rad?? maybe this is why the water temp at the rad is always cold as it is not circulating thru the core???? is that how a heating system works???

 

where do you live and how cold is it ?
what does your trucks temperature gauge read after about 5 minutes of running ?

something is not right. after 5-10 minutes of running, if your thermostat and water pump is working right, here's what you should have: temperature gauge on dash should read about 195*F. both of the heater hoses should be too hot to hold. top radiator hose should be too hot to grab hold off, approx 195*F. radiator should have pressure build up, and opening it should spew near-boiling coolant everywhere - so don't do that. the top drivers side of the radiator should be too hold to hold. the lower passenger side of the radiator, and the lower hose should be much cooler - possibly cool enough to grab hold off, depending on how cold the weather is.

the heater hoses work like this. hot coolant flows from the top of the manifold into the heater hose on passenger side, passes through the heater core and returns through the hose on the drivers side to the water pump pipe. both hoses should be very hot, both at idle and at rpm, and they should stay hot, no matter how long you rev the motor for.

now if you tell me the outside temperature is -20 or -40F, then all bets are off. you might have to take some extreme measures to get the engine up to operating temp (195 F)