I have an 03 Grand Caravan, 3.8 motor, 186K miles. I tried doing a search on temp problems but found nothing like the problem I have.

I live in the country, a trip to town starts out on 45mph roads for several miles, then 55mph for another six miles. Lately the water temp (as monitored by a Scangage connected to the OBD port) has been taking a long time to reach full temp. I takes about 9 miles at 45-55 mph to reach 195 degrees. Then it will fluctuate between 180 to 215. I thought the thermostat might be at fault, so I changed it (195 degree OEM part) as well as the water pump since it was making noise. The result was no change to the slow warm up. The coolant level stays full, no loss of coolant.

At the same time, neither the front or rear heater has been working. They never get very warm, not enough to heat the interior. I haven't done a system flush yet, will do that this week.

I'm not sure if the two problems are related or not. My main concern is the slow water temp rise and the fluctuation. Any ideas?

 

Strange? Are you in a norther area that has been getting real cold weather now. Had to ask. I ask because 8 or 9 miles in cold weather and fluctuating between 180 & 215 sounds OK. What are your outside temps now?
Did you see your old water pump? How'd it look?

 

Sounds like a blockage or an air pocket causing no heat and the fluctuating temperatures. Start with the flush. Maybe take the heater hoses off and flush the heater cores separately as well.

 

Thanks for the replies. 2therock, I'm in middle Tennessee, the weather has been in the 40's to the 60's. The water pump was making a squealing noise like a shot bearing would, when I took it off I found out 2 of the 3 pulley mounting ears were broken off. Otherwise the pump looked ok.
grswat, I'll try the separate flush of the heater cores.

 

Read up on calibration of the controls in another post near this one.

Here

 

Well, the 2 heater hose going into the fire wall, grab it with ur hand with engine running at operating temp. Both of them are suppose to be hot. If one hot and one cold, you have a clog heater core. If both are hot, problem will be on the electronic side. such as Blend door control failure.
If both of them are cold, then you have a flow problem. Probably because you didn't bleed the cooling system properly, or cooling system is not holding pressure(bad Radiator cap).
It is normal for the coolant temp to fluctuate between 180-210F. But your heat should be HOT when coolant temp is above 150.

 

Hey guys, thanks again for the inputs. I finally got to back-flush the system today, and do the control calibration procedure. The coolant still takes an abnormal amount of time to come up to temp, and the heater still doesn't work. I did find during the calibration that the heat is hot for a few seconds right after the procedure finishes then goes back to cold. So, it's looking like I need a new HVAC control.
I also discovered the radiator cooling fans turn on at 150 degrees. I need to look into that a little further. That seems a tad low, possibly not allowing the coolant to warm up normally...?
I have one other question, though. While I was installing the Prestone backflush fitting into the heater input hose, I noticed the heater outlet hose has what looks like some sort of inline plastic part, about 2 inches long...is this some kind of valve? A one-way valve perhaps? I did some online research on it, but no results on the net. Anyone have any ideas?

 

150 for the fan is wrong for sure so the temperature sensor may be toast. When the sensor fails the default is "fan on".