[elefantrider]

All it took was one good overheat and the heater core puked. Water inside the car and a lot outside.

Is there some kind of safety valve on heater cores?

The reason I ask is because after the engine cooled down, the leak stopped by itself.....

[poncho447]

There are no safety valves on heater cores, once it leaks it's replacement time. It's most likely leaking at one of the soldered joints under pressure.

[elefantrider]

Thanks. I guess no in-tank sealant is going to repair this. The heater core is higher up than the radiator/ engine so doesn't it leak all the time.

Am thinking maybe it depends on if the thermostat is open or closed?

[Pontirag]

when the cooling system is full the heater core is full but if it has a leak and being pretty high in the system alot of coolant will leak out.

like was said above. no way around it but to replace it.

I have seen a valve installed in the system in other cars like older corvettes. also in chryslers.

[elefantrider]

To remove the heater core, does the fender need to come off on an A/C car?

Who makes the best heater cores?