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Unknown cause of engine warning alarm

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eric_jacobson

New member
"My 2000 5.0 EFI MerCruiser wi

"My 2000 5.0 EFI MerCruiser with an Alpha I outdrive engine warning alarm sounds after boat is used for 1 to 2 hours. It only sounds when at low RPMs. All gauges read normal, and all fluid levels are good. Alarm stops when boat accelerates and then starts again when I slow down. I had the boat checked by mechanic. They originally thought it was the water pump but when checked the boat was operating within normal ranges. They could not recreate alarm condition, but thought it was a bad oil pressure sender. They did not have the part. I bought oil pressure sender and replaced it myself. Next time out engine alarm sounded again. Had boat checked by mechanic. Boat was operating at normal ranges. They could not recreate alarm, but thought it was low gear oil. They added and said that was it. Third time out same thing. Does anyone have any idea what could cause this kind of alarm at low RPMs but not at higher RPMs?"
 
Worn impeller reduces water fl

Worn impeller reduces water flow at low RPMs but may only increase block water temps just enough to set off the alarm yet the gauge appears normal. The proof is an increase in RPMs increases water flow and shuts off the alarm. When was it last changed?
 
I bought the boat used last ye

I bought the boat used last year. So I don't know when it was changed. My guess is that it has not been changed. Does the impellar need to be changed regularly?
 
"Impellers are rubber and take

"Impellers are rubber and take alot of abuse. Over time, short or long depending on use, the impeller takes a set and the blades get a curl set into them which reduces low speed water pressure. If the engine is ever run out of water for even 10 seconds w/o water to the impeller it will become ruined. Water is its lubricant.

Replacement should be based on use and time. High use; change it after 1 or 2 seasons. Lower use; change it after 2 or 3 seasons. Mine is low use and gets a new one after 2-1/2 seasons."
 
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