I have a 99 grand caravan w/3.8L. Heat hasn't worked for months. Replaced thermostat, topped off radiator. Heat did come on the night that the t-stat was replaced but not since (2 weeks). Checked coolant level yesterday and today and poured over a gallon in to radiator but it sucked it right up. Seems like a leak but I cant find one. What's the capacity of the coolant system? Is there a place where it could be leaking taht I wouldnt detect? There's none on the ground under the van. Any help is appreciated. Thanks

 

Did the heater work after you filled the radiator? If it did, then i would put a pressure tester on the radiator and let it sit for a while. Then see if you have any leaks. also ck the passenger floor carpet and see if you have leak too.

 

Do you have the rear heat/air system? If so, don't just check the passenger floor under the dash because there are coolant lines that run to the rear heater core.

Shouldn't they also check the rear cargo area plus under the body along the collant lines/hoses/clamps?

But this should leave coolant drips on the ground - unless you have a head gasket issue - that is why the pressure test of the system is a good diagnostic tool to find the leak no matter where it is at.