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I Have A 1999 Ox66 250 Hp Yamaha Outboard. Last Week I Was Running Across The Bay When The Overheat Alarm Came On At 4800 Rpm. I Let It Cool Until The Alarm Went Off And Restarted. After 2 Minutes The Alarm Came On Again. I Let The Motor Cool Until The Alarm Again Went Off. I Limped Back To The Marina At 1000 Rpm. No Alarms. They Changed The Water Pump And 2 Thermostats. It Runs Fine Now At Anything Over 1000 Rpm But Will Overheat At Idle. Exactly The Reverse Of The Original Problem. The Yamaha Dealer Suggested The Poppet Valves. Any Ideas?
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The PRV valve is used to dump excess cooling water at higher RPMs.At low RPMs the valve should be closed to let water circulate to the top of the engine. If the valve is stuck in the open position(due to dirt or sand) the top cylinders won't be cooled enough and usually the alarm will sound. Simple job to check it--just time consuming because of tight quarters. -
where is the poppet located? are there more than one?it isn't called poppet in the service manual. is it possibly the pressure relief valve at the bottom center of the engine?Comment
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That's the one.........Comment
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