1976 Mercruiser 233 Overheating - next steps

[Lancer76]

My 1976 Chris Craft Lancer with a Mercruiser 233 (Ford 351 W) and alpha R upper and lower sterndrive is over heating at high RPM while in the water but not while on muffs. Will idle along ok in water and muffs.
I've swapped the raw water impeller, new 143* t-stat, new marine water circulation pump, cleaned risers, cleaned t-stat housing, flushed & backflushed all hoses and passages with garden hose.

It seems to me that the raw water pump isn't supplying enough water to the t-stat housing/water circ pump. Today, I installed a short piece of clear hose on raw water intake hose. Ran the engine with outdrive in a tub of water. At idle the clear hose did not fill completely with water. Maybe 2/3rds full. It appears that air may be getting into the raw water pump.

My plan is to drop the lower unit again and maybe replace the raw water pump housing. Also will check the water pocket. Anything else I should check while drive is off?

 

[Bt Doctur]

Replace the complete pump housing top and bottom.and you cannot run in a tub, water level is not high enough to reach the impeller and you will damage it.

 

[Lancer76]

The tub does cover the intakes. Garden hose continually supplying water incase its splashed out
Why wouldn't that work? The tub is half of a plastic 55 gallon drum.

I like the idea of replacing the housing. Thanks

 

[Lancer76]

I see what you mean about the tub. Even if the intakes are covered the water level in the outdrive is not to the pump itself. Good point. Thanks.

 

[Scott Danforth]

The tub does cover the intakes. Garden hose continually supplying water incase its splashed out
Why wouldn't that work? The tub is half of a plastic 55 gallon drum.

I like the idea of replacing the housing. Thanks

because the pump wont prime. you need to get the waterline about 10" above the intake grates, or basically where the boat sits normally in the water.

so unless your tub is large enough to put the whole boat in, use the muffs