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1978 5.7/260 HP OVERHEATING

S

SUPERNUKES

New member
MY CONVINCER'S MERCRUISER OVERHEATS AT ANY RPM OVER 4000. SEEMS TO RUN FINE UNDER ALTHOUGH THE GUAGE SHOWS HOTTER THAN I THINK IT SHOULD BE. IMPELLER WAS SUPPOSEDLY CHANGED LAST YEAR THERMOSTAT ALSO. PRE-ALPHA OUTDRIVE. i'M ABOUT TO CHANGE WATER PUMP ANY THOUGHTS ABOUT WHAT MIGHT BE GOING ON WOULD BE APPRECIATED. THANX
 
MY CONVINCER'S MERCRUISER OVERHEATS AT ANY RPM OVER 4000. SEEMS TO RUN FINE UNDER ALTHOUGH THE GUAGE SHOWS HOTTER THAN I THINK IT SHOULD BE. IMPELLER WAS SUPPOSEDLY CHANGED LAST YEAR THERMOSTAT ALSO. PRE-ALPHA OUTDRIVE. i'M ABOUT TO CHANGE WATER PUMP ANY THOUGHTS ABOUT WHAT MIGHT BE GOING ON WOULD BE APPRECIATED. THANX
 
Replace water pump first. Make sure to replace wear plate under impeller. stuck closed thermostat could also cause condition.
 
How old are the manifolds and risers? They can cause this problem by restricting flow at higher rpm.
 
Please bear with me guys. What is the wear plate? Does it come with the water pump or is it a seperate part. Manifolds and risers are original 1978 (I think). How do they restrict water flow. Thanx for the help.
 
The wear plate comes with a new impeller kit. It is in the drive, below the impeller. Manifolds can cause a restriction when their cooling passages clog up with rust. That causes the water to not flow enough.
 
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