Chrysler Repair: Coolant leak: Caravan, dodge grand caravan, coolant level

Question
QUESTION: 1999 Dodge Grand Caravan 108k 3.3L Engine
with Rear A/C and Heater

I am loosing coolant in this van. Coolant is leaking inside from underneath the dash on driver's side. First I thought, its the heater core. However, I refilled the radiator/reservoir with coolant. Turned on the heat and checked, there was no coolant! Few days later, it happened again and now my observation is that:
1) It happens when the A/C is used,
2) It happens after the engine is shut down (I usually see the coolant leak after I go back to van for next trip),
3) Does not happen when heater is used,
4) It does not happen after coolant level is dropped to a certain level in the radiator (will not happen again until I refill radiator),
5) I have also started hearing a hissing sound from both (front and rear) evaporators after the coolant started leading (but there is no change in the A/C performance).

Any ideas are greatly appreciated. I am just not able to understand why A/C would cause coolant to leak from a heater core area? I am a home mechanic and will be able to check anything in the engine if you instruct so for further clarification.

Thanks for your help.
ANSWER: Hi Shafique,
I believe for coolant to be leaking inside under the dash that it has to be related to the heater core or the piping that goes to it or the accessory heater (though that branching off occurs on the right hand side of the van so that is probably not the location of the leak). I suspect it is a very small leak that is pressure/temperature dependent in the quantity that is released and also that when the coolant level is lower than the leak site that the leak will be minimal and instead leak vapor (the hissing sound, perhaps). The pressure in the cooling system will be higher if the AC is in use on a warm day, and also shortly after you turn off the van's hot engine due to loss of circulation through the radiator. So that would explain why the leak only occurs after you refill it and when you let it sit and then find the leak upon your return. When you use the heater the temp and pressure in the system are lower so the amount leaked will be less if not minimal.
I have the procedure for removing and replacing the heater core which I could Xerox and postal mail to you at a copying cost of 9 cents per page plus postage. You might want to try using Bar's Leak on the system to see if you can plug the leak that way. Let me know a postal address if you want those materials.
That is my best explanation.
Roland

---------- FOLLOW-UP ----------

QUESTION: Thanks for the detailed answer. It definitely answers my questions. Actually, it reminded me of a similar leak few years back, and the radiator was leaking only after the engine turned off; I found that a screw coupling was loose. Maybe there is a similar piping leak in the heater core. I have Haynes manual, and looking at the procedure (how many other things I need to disassemble to reach the heater core), it is not possible for me to start replacing the heater core at this time. So I am trying to figure out something. I will highly appreciate if you can give me your input on following:
1)   I believe there is no heater valve in this van, so I cannot cut off the coolant supply to the heater core (i.e. coolant always flows through the heater core no matter what is the temperature selection switch); is this right?
2)   If there is no heater valve, then my next option could be to bypass the heater core (connect the heater hoses in the engine compartment with a coupling). This will at least solve the problem temporarily until I get the time to replace the heater core. Do you agree that this is a possible solution without any negative effects?
3)   This is related to no.2: If I bypass the front heater core, will if also disable rear heater? Is there a way that I bypass the front heater core and still able to use rear heater?
4)   Can I keep using the van with the reduced coolant level in radiator? It is not too low; I can see the surface of coolant from the radiator mouth. There is no indication that the engine is overheating even with A/C on and it does not leak anymore coolant at this level; at the same time the reservoir bottle is empty. What is your opinion if I keep using it with this level of coolant? Do you see any potential damage/problems arising from using the van with low coolant level?

I do not want to use Bar’s stop leak as I have head stories about it plugging the complete coolant system; I am just afraid to use it.

Thanks for your help!!!
And thanks for offering the Xerox from the factory manual. When I will decide to tackle the complete job, I will definitely like to get those instructions from you in addition to Haynes manual.


Answer
Hi Shafique,
1. Correct there is no cut-off valve for the heater loop.
2. No problelm with by-passing as far as I know; I did it on a VW when there was heater core problem and it worked out fine.
3. I doubt that the rear core is in series with the front core, so there should be no issue with that either, though I don't have a diagram of the system.
4. I don't think there is an issue with reduced coolant level but I would carry spare coolant in a bottle in case you start overheating due to losses.
Thank you as well for the kind evaluation.
Roland