overheating

I’ve had issues recently with my Universal M25 overheating after 5-10 minutes of run time. I’ve replaced the thermostat, coolant pump, impeller and a few of the hoses and verified the heat exchanger isn’t clogged. I bled the air out and made sure the coolant was flowing thru the thermostat...

Checked impeller and its not damaged. Diesel engine overheating and raw water is not exiting back of boat. No antifreeze or coolant. What now?

I have a 1984 Oday 28 with a 10 HP Universal Diesel inboard motor (now know as Westerbeek). I've been having over heating issues and getting help from 2 marine engine shops. Replaced thermostat, heater hoses, impeller, radiator cap and removed and cleaned out the exhaust manifold. Shop says...