over heating above 3000 rpm

[rharry]

1973 mercrusier 302 888

Replaced stern pump, replaced thermostat, removed and cleaned manifolds and risers, also have checked all incoming lines for clogs, and engine still overheats above 3000. At 2500 rpm motor seems to run hotter than normal, but fluctuates up and down. Is it possible for the circulation pump to be bad even though there are no external signs of malfunction. Any help or suggestions would be appreciated.

R. Harry

 

[bomar76]

Re: over heating above 3000 rpm

Retarded timing will also easily cause overheat.

 

[jerryjerry05]

Re: over heating above 3000 rpm

How old are the risers/manifolds? Even if you hot dip them they are still probably clogged.If the impeller came out in 1 piece then it's probably the riser/man.Jerry

 

[PINESOL]

Re: over heating above 3000 rpm

its very possible your circulation pump could be bad without signs of leaking ... i would verify the actuall temp of the engine with a hand held laser or ultra red thermometer they are actualy pretty cheap .

 

[rharry]

Re: over heating above 3000 rpm

Thanks for your ideas so quickly.
I purchased the boat 4 years ago, really no idea if or when the manifold and risers were replaced. There was a lot of rust if them. I'll check the circulation pump this week though I'm not sure what to look for if it's malfunctioning. I don't mind changing the manifolds and risers if I can be reasonably sure they 're the cause of the problem. In the process I found a water leak near the bell housing. I can't tell if it's the lower exhaust elbow or the bellows.I do know that it's water on its way overboard. I assume this would not cause it to overheat at higher rpms.

rharry

 

[chiefalen]

Re: over heating above 3000 rpm

35 year old boat. Manifolds could be clogged, risers could be clogged, engine mounted water pump if never changed don't have any vanes left. You have a heat exchanger? Check if the lines are clogged common problem. Exhaust flappers broke off and clogged the exhaust?