- 2000 Dakota w/ 3.9 -
Last fall (2005) I flushed the cooling system. Prior to that the heater worked great. On the coldest winter days you couldn't leave the heat on all the time cause it would blow you right out of the truck. So basically it was awesome.

So...at the same time I flushed the system I replaced the thermostat because it was leaking around the gooseneck. After doing that work I was only getting luke warm air from the heater system. I decided I could live with it last winter. I thought maybe I got a bad thermostat since I got the economy version. So a couple weeks ago I put in another thermostat. Higher quality version this time. But it seems I've got the same issue with luke warm air. I figure it could be one of the following problems:
1. Heater core clogged after flushing the system.
2. Fan clutch not working correctly, causing the fan to keep spinning full speed all the time and keeping the motor too cool.
3. Temperature sensor not working correctly, althought I don't know what this would really do since the computer doesn't control the fan speed on clutch fan. However, I do have an electric fan that is in front of the clutch fan, but I think that's a transmission cooler fan. Not sure though.
4. The heat control **** and door assembly is not allowing the heat door to open all the way which allows a mix of hot and cool air in resulting in only luke warm.
5. Air in the cooling system.
6. Bad thermostat staying open all the time.

I think those are all the things that could cause what I'm seeing. Now, trying to deduce what it might be....
1. Heater core...I've checked both the supply line and return line to the heater core when the truck is hot. Both of those lines are hot. Really to hot to hold on to for more than a few seconds. So I think the flow of coolant is good through the heater core. But maybe it's partially clogged?? Is it possible for a partially clogged heater core to cause this?
2. Fan clutch...I'm not really sure exactly how this is supposed to work. I know when the motor is cold I can spin the fan with little difficulty. When I turn the truck off and the motor is hot, I can turn the fan with no problem. So I don't know if this is correct operation. Does anyone have a 3.9 Dakota they can check for me? Does your fan do the same thing when the motor is hot and cold?
3. Temperature sensor..As mentioned above, I don't think the temperature sensor is bad. The inside temperature guage always registers about 190 degrees when the truck has warmed up.
4. Heat control ****...I think I'll have to tear part of the dash apart to check this. I've looked under there but it's not obvious to me exactly where the air mixture door is.
5. Air in the cooling system...how do I check for this and could this cause luke warm air instead of hot?
6. Thermostat...I don't think it's the thermostat. This is the second one in a little less than a year and both times I've gotten the same results. the water running through the top radiator hose is hot, so I'm pretty sure the thermostat is working as it should.

Does anyone have any helpful hints? I'm most concerned with the potential of a partially clogged heater core. Because it seems this problem started after I flushed the system last year.

Thanks...Bill

 

temp sensor is only good for the gauage and for the comp to engage and disengage the fan clutch.. the heater core maybe clogged... but if the lines are hot.. that shouldnt be an issue.... id think ts soemthing electrical.... cause whenever i turn my blower on in my truck , i got a 3.9 as well, it takes like a few seconds for it to actually turn on.. so there maybe a problem there... and with the cooling fan, mine is engaged when the truck is cold... so basically everymorning heading out.. i have my truck idling for 5 minutes... 1/4 the way there warm, i hit the gas going down the road... you hear and feel the fan engaged... but then shuts off... its weird.. at what temprature does your thermostat open?....

 

I have The same problem On a 2001 dakota 3.9 I just replaced the heater core and thrmostat the heat is luke warm at best I let the truck run when i first did this and the heat seemed good but ever since then it has not been right . I relly do not look forward to taking the heater core assembly back out fearing i did something wrong. Thanks and also I learend about the heater blower risistor problem very helpful and informative website. Glenn

 

i have the same problem as well. in an earlier thread, many people suggested reverse fluching the heater core. this seems logical as a temporary solution but i imagine it will get clogged again. any opinions? i already have a new heater core sitting in my garage, i am just not looking forward to having to install it. i havent done it yet and from what i hear from my friends, it is a major PITA on the dakotas.