My cooling system has a small leak in heater core. (1987 Lincoln Town Car.) Bars Stop leak has reduced it but not completely. If i keep the radiator fluid level about an inch from full, (when cold) it greatly reduces the heater core steam. Which means the cooling overflow tank stays empty. Engine does not run hotter because when it gets hot the fluid fills the radiator.
There is no antifreeze smell or steam when air conditioning is running.
I assume that since the radiator has a small air space in it, that it reduces the pressure, therefore the leak stops.
If the car has a 16 lb radiator cap, would using a 13 lb cap instead have the same effect? Reduced pressure means less or no leak in heater core.