Marinised Kubotas pressure problems.

[hotponyshoes]

If it was the heat exchanger the raw sea water should start coming out after it's pumped the coolant out, ie. It wouldn't just pump coolant out, it would then keep pumping sea water out afterwards.

With the engine now out I suppose you could check for salt in the coolant.
Don't know how though. Wouldn't want to taste it as antifreeze is a poison.
Boil it away (outside) and see if it forms any salt crystals?

It can't be that hard to pressure test the heat exchanger if you can get access to both fittings

 

[pedrobedro]

Is the engine coolant pressurising but not overheating ? That doesn't sound like a head gasket type problem which really only leaves the heat-exchanger. Does it still do it if you run without the header tank cap ?

 

[the snooper]

Don't see how it's the heat exchanger unless the exhaust is partially blocked and the exchanger has a crack , a simple pressure test will confirm that, it' not running long enough to overheat, I'd be looking at a cracked head or cylinder