Ok, this is my third post on this subject. My 99 3.9 is driving me crazy because I cannot get any heat out of it!! I have flushed the heater core twice and did a reverse flush as well. I have replaced the thermostat and still no help. The other night I was driving it about 40 miles and the temp kept going up and up and up. By the time I reached my destination, it was overheating!! It is 5 below outside!!! Something is wrong. That is when I changed the thermostat. The fan blowing on the radiator runs constantly!!! Like I said, it is 5 below outside and when you turn it on right away in the morning it is running!! Could I have a bad radiator??? The lower radiator hose is not very hot when it was overheating.....? Please help!! I am selling my car and will soon be relying on this truck full time again. I dont know if it matters, but I do need a new evaporator. I know that and the heater core are in the same place, could the evaporator going bad affect the heater core??? Now you know EVERYTHING!!! THANKS!!!!!

 

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could very well be that the cores in the Radiator are plugged.

I bought a rebuilder Dakota and had to buy a new Radiator for it.....

Shop around, I think I paid like $150 (include a lifetime warranty)....
Of course I did alot of shopping on ebay for prices and took that to
a local shop so if I had problems that I could get it fixed locally.

I also put on a new water pump for around $30....cheap insurance


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Sounds like something is blocking water flow. You either have a blocked or plugged radiator or the system is air locked somewhere. My guess is time to replace the radiator.

 

Check to see if there is a coolant leak. Recently I had a friend who had this problem as well, she said she had just gotten her thermostat replaced and it worked for a little bit, but then her heat stopped working. Turns out, the guy who put the thermostat in didn't refill the coolant back up. See if there are any leaks, so if its low, and if it is, you should bleed the system out and fill it back up with fresh coolant, it worked on her vehicle..

 

DUH on my part.. one more important afterthought. you said -5 degrees. the last time is got real cold here in GA. everyones cooling system FROZE UP which causes no coolant flow and overheating. test your anti-freeze level to ensure that its good for -20 or -30 degrees. don't assume that its good just because its green. mine was green the last time it was froze up and i was stuck on the side of the road. you may need to put a piece of cardboard in front of the rad.


based on your descriptions..
1. temp gauge show over-heating yet the rad and lower rad hose is cool..
2. no heat from heater.
---assuming your temp gauge is correct---
it sounds like you have a coolant circulation problem, which is resulting in overheating, and also poor or zero flow through the heater core.
it could be a simple air pocket, but its more likely either a bad thermostat blocking flow (or possibly in upside down) or a bad water pump (or slipping belt) that is not circulating the coolant through the system, or perhaps a blockage in the upper/lower hose or radiator.
i'm betting on water pump.
but, for proof, you could try a couple of thing..
1. remove thermostat completely. this will NOT give you any heat, and will also probably trip a CEL 1281? (engine warming up too slow), but it should resolve the engine overheating and at least make it drivable. it will also give you a chance to inspect the thermostat to make sure its not in backwards. the sensor should be down, inside the manifold. (sorry, sometimes that happens).
2. check upper and lower rad hoses to make sure they are not blocked by something (unlikely) and make sure they are not collapsing under low pressure.
3. check radiator flow by squirting garden hose in the upper hose port and seeing it drain freely and heavily through to the lower hose port.

i'm guessing your water pump is shot.
i'm sorry its -5* degrees there, as that makes working on the truck about impossible, especially with water and drainage involved.

afterthought.. i don't know anything about dakotas... you said the fan was running. are you talking about an electric fan ? they are generally turned on by temperature sensor (which could be bad) or Air Cond on, or possibly ??defroster on??(not sure). this might or might not have something to do with your overheating problem.

 

thanks for the quick replies!! I was thinking maybe the blocked radiator as well. dhvaughan, I am really wondering about the fan. It is the fan that blows on the radiator. I do not have the ac on or defrost on. This fan is connected to the water pump. Isn't there a 'clutch' on this fan that could be bad?? Like I said, I JUST replaced the thermostat last night! Yes, it is in there properly...I know, I thought of that myself. I dont have a coolant leak, I have checked and when you park in snow, something like that is easy to spot. Do you guys think I should replace the radiator and the water pump while I am at it???? I think I have exhausted all other possibilities, right?

 

kcoop, i just editted my post to consider possible freeze up. please see above.

 

the clutch fan is really only a "soft start" device that is design to slip when necessary, as opposed to killing cats and cutting your hand completely off. since its attached to the water pump, which is attached to the drive belt, it will always be trying to turn. failure of the clutch fan is usually a complete freewheel, which means that its not really turning, which leads to overheating in hot weather. a normal clutch fan will turn easily with just slight resistance. when spun hard by hand it will turn a little and then stop. a bad clutch fan will continue spinning.

your clutch fan sounds normal and i don't think its related to your problem.

i'm thinking you either have a blockage, a freeze up, or a bad water pump.

 

alright, just got back from a short trip around town and it is overheating again! I sounds like something 'clunking' in the overflow tank... could it be ice?? There is definately no flow through the system. So, like you mentioned....probably a water pump(?) Is there a sure fire test from here? Thanks Again!!

 

moe in wichita ks
all of the above are things to check. but if the system is air locked, just drill a 1/8 hole in the stat so the air leaves the engine. this IS a factory enginers aproved. i read story about some overheating stright 8s in the fourtys. the enginers found that the new co. that chrysler got to make the stats was use to making close tol. valves. and the stats was air tight. so the enginers just drilled a small hole to let the air out. not hard to do.