grand caravan with heater problems

I have a 2001 Grand Caravan the heater no longer blows warm air when the van is started (even if it is left to set and warm up) but will once it has been driven for about 5-8 minutes. However if the van is stopped at a light or another reason within the first 20 minutes of the drive the heater will begin blowing cold air. The strange part is that once the van is totally warmed up say after a long drive of 30-45 minutes then the heater will work fine for the remaineder of the day when left parked for short intervals of an hour or two. Any ideas or suggestions????

If your thermostat was stuck open the heat would be much slower in building in the system. Another thing I would look at is to make sure the radiator is full. If there are air pockets the circulation may not be what it should be. What does the dash board engine temp gauge say while all this is going on, is it reading cold hot etc?

The temp gauge reads just below mid point between cold and hot. That tends to be it's usually position.

In theory: Coolant circulates constantly through the heater core. it is moved by a properly functioning water pump. The thermostat is to open only when the engine has reached it's optimal temp.. Once it opens it sends coolant to the radiator to keep the engine from overheating...I'm not sure of the temp on our Caravans but most vehicles are around 180 degrees. If your thermostat is stuck open, even if only partially open. The radiator is taking heat out of the coolant the minute the van starts to run, and a radiator does a really good job of exchanging heat. So instead of 170 degree coolant circulating though your heater core maybe it only gets to 125 or so ?? That can make a huge difference as far as the temp of the air coming out of the heater vents.

You may also want to check the electric fans on the radiator, they shouldn't come until the engine is hot...they are thermostaticly controled. and the
engine coolant temp sensor controls that.

There are also ventilation controls..dampers that channel the air movement around the heater core or the AC evaporator. When the controls are set for heat/AC or defrost these dampers move to channel the air the right way to get the result you want. If these controls aren't working properly you'll get outside air being channeled in when what you want is inside air being re-circulated around the heater core. This does happen sometimes

You could have some kind of a blockage in your heater core...not real likely. but you can have aproblem with them. You could have a problem with your water pump not circulating well..but you might have overheating problems in the summer if that were the case.

I think your best bet is on changing the thermostat. Someone else might have a better idea on how to check the thermostat. One way that comes to mind is...with a cold engine start the van and quickly and carefully remove the radiator cap there should be no flow of coolant...it should just be sitting there like water in a bottle. if it is flowing your thermostat is stuck open.

Spit

Thanks so much!!! It took awhile to figure it out but all of a sudden it started working so we are pretty sure it was the air pocket. We had to add coolant three different times to get it to work right and we added a new radiator cap for safe measure but all seems to be well now. In addition, through conversation at a recent gathering I found that a family friend had been having the same problem with his car for over a year. I relayed the information you had given. He had already tried changing his thermostat twice and was grateful for another option. He called yesterday to tell me that after filling the car up twice with coolant his defrost is running great! Thanks again for the information.