I'm a fairly new owner of a 98 Baja outlaw with twins 454 Merc's. Over the weekend my passenger side motor started to run hot. Pegged @ 240. It was beached without pulling the drives up. I had a mobile repair $ervice guy replace my impeller which he said the original one was in great shape. He suggested maybe the thermostat was stuck causing it to over heat. I completely removed the thermostat and still continues to over heat

I pulled it off the water and hooked up the hose to the out drives and figured I could try to blow through out what ever sand it suck up. I disconnected a line on the thermostat intake and noticed not much water was going throughout the manifold. I turned up the water all the way and it got more water exiting but not in comparison to the out put from the other thermostat outlet on the other motor. Under the swim step the left exhaust outlet was running almost dry.

Back on the lake it ran cool for few minutes then overheated. I pulled off one of the lines from the thermostat manifold and it was just barley spitting out water now. The impeller is new and thermostat is out.

I really hate to take it to a shop and pay someone to figure this out. I'm assuming there is a clog somewhere. Maybe the sea strainer is if even has one. Is there a regular water pump in the engine like a car that is seized? How do you back water pressure the system? Any suggestions would greatly be appreciated.