Plymouth Voyager Heater Core Leaks and Transmission Problems

Reader Question I took my 1999 Plymouth voyager to Autozone, for one of their free diagnostics. I took it because on occasion the front window fogs up in the heat of the day. Also the service engine light is coming on,and there is smoke under hood, there is a wet spot inside on driver side.

Guy at Autozone said my problem is a transmission shifter solenoid. My dad thinks it is Heater core. What do you think? What manual would you recommend to get to help in replacing both these items? My dad is a mechanic, but he is more familiar with older cars and big 18wheelrs. So he would need some guidance in placing these for me.

Hey Jody

Well it does kinda sound like you have a leaking heater core to me. I would check the coolant level inside the radiator, if its low you have a leak. You can get a cooling system pressure test to verify your heater core inside the dash is the problem, but most likely. The wet spot on the floor inside probably feels greasy, since it is coolant/anti freeze that leaked.

That will cause the leak inside the driver side, and the fog on the windshield but the leaking heater core will not cause the check engine light to come on…unless there is another coolant leak under the hood that is spraying coolant onto a sensor. Since the heater core is inside the dashboard, and you say you have smoke under the hood..I would suspect you have another coolant or oil leak under the hood.

I would get a pair of vice grip pliers or go back to Autozone and tell them you want to “bypass” your heater core and want to buy the plastic heater hose splice needed to hook the two heater hoses together…by passing your heater core. Your heater will not work, but since it is summer I don’t think you need it right now anyway.

Once you by pass the heater you should either get a cooling system pressure test OR keep a close eye out under your hood for another coolant leak, or oil leak that would cause your under hood smoke problem.

Once you get those two problems under control then determine if the check engine light is really a problem or not. I would not do anything with the Transmission solenoid at this time if you are not experiencing a problem with the transmission…and Autozone is not the place for that kind of repair anyway. A real transmission shop should read your computer codes and go from there …..if you are still having a problem.

Here is more info on the heater core

Heater core problems

Austin C. Davis

Reader follow up

By passed the heater core, solving some of the problem. But it still acts like it doesn’t want to go when on freeway. Could that be the Shift Solenoid, guy at Autozone told me about?

I called a transmission shop, they said this was and external part. Where could we find pictures of this part and it’s exact location? Is it also called a Transmission Control Solenoid?

Hey there Jody

I am not a transmission mechanic, so I would really like you to take the vehicle to the transmission shop and have them at least take a test drive with you and let them give you their opinion as to what it could be. I have never replaced that solenoid, nor do I have a picture of it…and I Googled it as well and did not see one either.

I just do not believe in Autozone enough to feel comfortable telling you to go ahead and replace that solenoid. I would rather see you spend a little bit on a proper diagnosis at a real transmission shop before you just start replacing parts. Your local regular mechanic will probably go on a test drive with you as well…to get his opinion if it is a transmission or engine problem.


Austin Davis

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