Evinrude 9.9/15 overheating

[driver0606]

I have a 1989 Evinrude 9.9 with 15hp carburetter on a 9 ft. speedboat used in salt water. In the last 4 years it has always been flushed out with fresh water at the end of the season. It started running too hot last year. The impellor looked OK but was changed and the thermostat removed, without improvement. I then took the lower unit off again and connected a garden hose to the tube that runs up to the powerhead, with the thermostat cover off. For a while there was no result then suddenly water began to flood out. Once reassembled the engine ran normally at all speeds.




This year the small stream of indicator water runs just warm at low speeds, but gets very hot/boiling if the engine is run at max power. I prefer not to strip the engine. Any ideas, please?

 

[oldboat1]

Take the cylinder head off, and check for salt deposits in the water passages. You may need to scrape them out with a thin blade.

 

[driver0606]

Thanks. However, when I removed the lower unit and the thermostat housing (on the top), everything was perfectly clean, as was the water when it eventually it started flowing out. The mystery was, what could initially blocked the water flow up from the water pump pipe when I attached my hose? The water, when eventually it came, looked clean. Maybe I should repeat the flush, or perhaps reverse it by attaching the hose at the thermostat housing?

 

[tomhath]

You can also do that if you want, but removing the cylinder head is an easy task and there's a very good chance the water passages are blocked.

"The mystery was, what could initially blocked the water flow up from the water pump pipe when I attached my hose?"

Salt.

 

[flyingscott]

Try salt away in a garbage can.

 

[driver0606]

Thanks guys. I tried salt away, but its no better. I'll take the cylinder head off.

 

[kbait]

Put a new thermo in. I had one overheating after impeller change, checked thermo and it was stuck open. Replaced it, and cooled normally. Doesn’t make sense.. but system must need some back pressure for cooling water to flow through correctly. (freshwater motor early ‘80’s 15hp)