It's a bit of a mystery...
82B with 1500 hours, well maintained.
expansion tank fills to the brim after I run it. I've removed about 3 liters and it keeps filling. I naturally assumed it was a problem with the heat exchanger
but a coolant
pressure test to 14psi shows no drop in pressure.
Perhaps when the HE is at temp a slight leak allows raw seawater to leak into the coolant
system. The head gasket
seems OK as there are no bubbles in the tank.
I replaced the 2 pressure caps. My next step is to test the coolant for proper ratio, 50-50. If low, I'll then pull the HE and have it checked or replace it.
I can't think of any other possibility?