Coolant loss

Can anyone help? I got a late start this season, but I replaced the heat exchanger, manifolds, risers, elbows, spacers, stainless blockoff plates and gaskets on my port 270 fwc Crusader. After a 20 minute 5 mph ride from our marina to our mooring and back last Saturday, I lost a gallon of coolant. It’s not leaking out into my bildge, and it’s definately not a blown head gasket. Engine is running perfect, and at a 5mph ride the engine stays at 170 degrees. Also oil level is right where it should be, and oil is pristine! Has anyone had a similar issue. I’m thinking maybe a bad intake manifold gasket, but have found no posts in regards to a coolant leak due to a faulty intake manifold gasket. Can anyone help?! Thanks!! Ken

First question is did you purge the cooling system after the reassembly?

If yes, then start with a real good visual inspection.....especially where there is a hose clamp....if you don't find anything there, get a radiator pressure tester....

All hoses and clamps are new. There are no noticeable leaks anywhere on the outside of the engine. And absolutely no coolant in the bildge. This is why I’m totally stumped. The only thing I could possibly think it might be now, is a bad intake manifold gasket.

Oh, and yes. I’ve run the engine and topped off the heat exchanger numerous times.

I would have the heat exchanger pressure tested even though you replaced it.