Today I removed my leaking heater core, and discovered that both halves of the housing, as well as the heater core itself are installed with some form of gasket. It looks as if it was squirted in the groves then the housing closed, forming a gasket. This was in pretty bad shape and also soaked with coolant. My question is, can I re-create this with black RTV, and apply it, wait for it to skin over, then compress it so it forms to the cavity but not bond? Any advice would be appreciated. Thanks.

By the way, thanks to everyone for all the writeups on how to do this swap. I have a 97, so it was slightly different, but still manageable.

 

swapped my heater core last weekend so I know exactly what you are talking about. The RTV helps direct airflow through the core. you can use rtv or foam window sealant from the local home improvement store. I used just a dab of rtv and everything turned out fine.

 

It likely was caulking that was used. You can pick up some butyl tape to recreate the factory seal. RTV works as well, but may be more difficult to clean up unless you spread it nice and even and let it setup.