5.7 mercruiser overheating

[nathanclarke]

my mercruiser 5.7 overheats when running full wot for a couple minutes i slow down to 3000 rpm the heat gauge falls back as long as i sail under 3500 rpms no problems. the moter is raw salt water cooled ,i changed the thermastat 160 still the same the engine is 1991 thanks

 

[Don S]

Re: 5.7 mercruiser overheating

When was the last time the impeller was replaced?
Being in salt water, have you ever inspected the exhaust manifolds and risers. They don't usually last more than 8 to 10 years before plugging up or leaking water into your engine.