I have flushed the system multiple times and replaced the thermostat. It takes for ever to warm up when it's cold outside, I can start it and let it idle for 10 minuets and defrost will hardly melt the ice off of the windshield and the temp needle hasn't moved, I have never seen it get above 160 or so since I have owned the truck. I thought the temp sensor might be bad but when I read the temp with the temp gun it is close to what the gauge shows. What else could cause this? My Jeep 4.0 heats up to 200 in 5 minutes in the same weather, even my 7.3 diesel heats up quicker than this.

 

my 3.9 somewhat has the same problem, it gets between the middle temp and cold level, even with the fan and clutch removed (did the water pump and never put the fan back on, its 20 F here so im not worried and will put a new one on in the spring or something). So maybe your fan is always spinning? also i think the radiator is overkill for the small 3.9. I might block half the radiator and see.

 

Think I would start by replacing the thermostat........

 

For cold climates, the FSM suggests a "winter front". It used to be a mopar kit.

Yes, the V8 radiator is a touch oversize for the V6, and the factory tune is a wit bit on the rich side, so the extra fuel cools it off a bit. It's very much a cold-natured beast. I can watch the thermostat open and close on mine idling through the OBD2 interface.

 

Even if the radiator is oversized the thermostat shouldn't open until it gets warm enough. I have a new thermostat in mine.

 

What brand/temp thermostat did you install? They are not all created equal......

 

Stant thermostat I think.

 

Usually a good brand.... Still, I would be tempted to pull it, and test it.

Not a 'safety stat' by any chance is it??

 

Coolant system is full and burped, yes?

 

Well here's ANOTHER 3.9 owner who has this SAME problem ('94 Dakota)... Like so many others I put a new thermostat in - just the other day - and it has helped maybe 5 degrees worth.... In other words, not enough to help me stay warm. Now I live down South, but ya know what? - it gets COLD down here too. And I don't DARE take this truck out if we're expecting sleet or ice. There is nowhere near enough heat to keep my wipers from freezing to the windshield. This thing will NOT heat up running down the road or sitting there idling.(I thought at one time that maybe I was getting too much cold air coming in and overwhelming the thermostat). I have FINALLY decided to do the old "cardboard trick"... you know-> cover half the radiator with a piece of cardboard. Aint it ridiculous to have to do something like that?! And while I'm on here, would someone PLEASE tell me how to start a new thread? ("THANKS" - sorry for being so stupid)