1990 245 LTD - OMC 460 - Overheats if not trimmed down. going on 3 seaons
 

So, my OMC 460 has been running perfect for 20+ years. Now it's over heating. The raw water pump (which is inside the lower unit) King Cobra, exploded. I picked up all found pieces from the top of the oil cooler behind the block. Replaced the raw water pump. Should be dandy, right?
WELL... not so fast. Still over heats. I then remove the exhaust system - found nothing, but I soaked the elbows in rust remover. Definitely removed rust. No change.
Tested, using the 600 page OMC manual, the raw water pump. Engine running, boat in water flat, shoots water easy 4-5" in air.

Used metal rescue rust removed IN the block. Warmed engine up, drained. Filled with 4 gallons of this, and let sit over night.
Still over heats, but takes longer. Also, what I discovered just a bit ago - trimming DOWN makes it run nice and cool...
Sometimes boat would over heat. Couldn't figure it out for the longest time. I also removed the recirculation pump - nothing wrong w/it. Also no such thing as this pump any more, so I had to reinstall it. - No change.

So, now what I know is; keeping the trim down, keeps the engine cool, but kills the performance, and the prop is definitely not aligned with the level of the boat.
SO, now my question... WHAT IS IT?! I believe it's a flow restriction between the raw water pump and engine. And by restriction, I mean, is there a rubber hose that connects the two that I'm not seeing on a diagram here?
and when that hose becomes stretched after 26 years of use (and always stored with lower unit way up) it's leaking?! Am I losing water pressure, and it's leaking while running at 3800 RM

any help would be great! Because it still "works" and because OMC460 parts are so freaking rare, I'm planning to take the lower unit off this fall after I winterize it... I don't want to spend 3 weeks waiting for parts in August, if I can be on a boat.

So, there it is, wife and I love this boat. Can't wait to buy bigger, but we will both be devastated to let this one go.

A part # would be great, or anything. I've tried 3 thermostats. Verified all worked. Tested gauge. All good. Definitely overheating - only under load and only if trimmed up to a 'running' level. (not over trimmed).

https://www.marineengine.com/parts/o...odel=754APEPWS

is the best diagrams I've found so far...

My next one will be 5.7L or 6.2L engines, much more common...

Look for a hose between the helmet and the outer transom assembly. See if it is weak or kinked with drive trimmed down.

Found said hose last night. couldn't see much, but it appeared to be in good shape. I'll tear it apart this fall once she's winterized.