re: Yamaha 90 HP overheating while peeing

I suggested this earlier as well.

Mine is a two stroke and would pee, but the temperature alarm would sound when it overheated. Upon further inspection, debris from the old impeller was partially blocking the intake port and not allowing enough water to get to the impeller.

quote:

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The original impeller was broken off in several places.

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You need to pull the thermostat out and leave the lower unit off. Without running engine, try to back flush the thermostat port to release the missing blades of the impeller you couldn't find.

ETA: thermostat covers are usually 4 bolt covers connected to a 3/4-1 inch rubber hose.

ETA 2: thermostat cover bolts are very brittle depending on age of engine, small, metric threads, and a bitch if you break! Be careless

Not familiar with that motor but some lower units have a plate that separates the exhaust tube form the coolant side. It’s about 3”x 3” and fits in grooves vertically to rear and just below the water pump baseplate. If it’s not sealed off with silicon at idle it can allow exhaust gas into the water inlet side of the lower unit and gas off the water pump enough to cause overheating. It’s definitely a thing with Mercurys and I think older Yamahas. Worth checking into because it can definitely make you pull your hair out if that’s it

Try a Rydlyme flush kit?

I blew air through mine first with an air compressor. Then found the right size plastic hose from Lowe’s to fit in the hole for a water flush. I wouldn’t worry about getting any of that wet. Water shouldn’t affect any of that and it all drains out the bottom.