I have a 1991 Dodge Caravan, 3.8 liter.

I have had this for about a year now. I recently flushed out the whole cooling system and added new coolant for the winter. I dont seem to get any kind of circulation for the heater core. I have replaced the thermostat. I have switched the hoses going to the heater core thinking they were hooked up backwards, but no luck.

What it is doing is, as long as I dont turn the heater fan on there is hot air coming from the vents and all, but as soon as I turn on the heater fan, it starts blowing cool air and if I turn the fan on high it will blow cold air. It is like the fan cools down the water going through the core.

I take the radiator cap off and it does not seem like there is much circulation going through the radiator. Once in a while I can feel the hoses at the heater core and they are both hot and then at times one is hot and the other cool.

Is their anyone out there that has had this problem and knows a fix, as it is now getting winter and my wife wants heat. I did not have this van last winter so I do not know if it worked before I got it or not.

Thanks for any help. Bob

 

Pull the 2 hoses off the heater core under the hood and take a garden hose and flush the heater core in both directions. There should also be a heater valve in one of those lines? It may be bad. When the heater core is circulating correctly and the engine is fully warmed, BOTH heater hoses should be real hot to the touch...if one is cold then there is no circulation.

 

I have already flushed out the core and took the valve out of the system. But for some reason there seems to be very little circulation. If anyone knows what could cause this, please help.

 

Sounds like may be time for a new water pump.

 

Do you really think it could be a water pump? That was my first thought, but was told by, what I thought was a reliable mechanic and he said that the water pump had no relation to the heater core circulation. I have tried all I could think of except the ater pump, so I guess I will try and replace it, doesnt look like to hard of one to replace. Thanks Bob

 

Bob, its not the water pump, are you having serious overheating problems? if not then the pump is fine.
Sorry to say but i think the core is clogged, i suggest you have it replaced.
Good luck

 

Sam or Anyone, Thanks for insight on water pump. I have no heating problems around town, but pulling a steep grade like 6 or 7 percent, than the vehicle will overheat some, but not totally. That is why it is probably not the water pump.

But I have flushed out the heater core from both directions and tried hooking the hoses up on different sides of the core, but to no solution.

I have been a certified mechanic in my past life, but not since the late 80's, and I have never seen this problem before, so I am really stumped as to what to do.

 

I figured from your description that when you flushed the heater core, you have real good flow coming out the other tube? If not, blow the heater core out with compressed air. Make 2 short hoses that you can attach to the heater core connections, fill the core full of distilled vinegar and clamp off both hoses. Let it sit overnight and try flushing it again.

 

I would have to say the heater core is clogged.

 

But like I said, I have flushed out the heater core from both directions and good good flow both ways, so guess I am at a dead end, because today I did change the water pump and no difference. I did fludh out the system again and put new coolant in and now at high rpms I seem to get a little warm air coming through, but at idle it blows cold again.

Thanks everyone for all the help, if I ever figure it out I will put a post as to what the problem was.

Bob