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Volvo penta 74 gsi problemsHELP

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86turbo

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i have a 1998 fourwinns 240 wi

i have a 1998 fourwinns 240 with the 7.4L volvo in it. We had problems with the engine before and completly replaced it with a rebuilt 7.4L about 2 yrs ago....the boat runs in a lightly salted lake thus causing some corrosion problems....

here is where i'm at.....the engine overheats at idle but will cool down slightly if run up to about 2500 RPM...then overheat more after that...once returned to idle the engine heats up even more...I've replaced the impeller on the water pump...replaced the thermostat twice....completly soaked and flushed the cooling system with a concentrated solution to clean up the corrosion....checked all hoses with water pressure to make sure water flows freely....no water in oil...circulating water pump seems to be pumping fine....yet the engine still overheats......

we are good mechanics but are stumped on this one...PLS give us some help if you can.

ps. the engine runs super rich and we've replaced the computer and had it re-programmed...
tried everything...

as you can tell we are in deep sh** and need some advice
 
"How old are the manifolds and

"How old are the manifolds and risers? Also, you may want to have a good look at the water circulating pump. If someone installed an automotive pump on your rebuild, the impeller may be cast iron and totally gone by now.

Also, how is the condition of the thermostat housing?"
 
the manifolds are from the fir

the manifolds are from the first engine and the risers are 2 yrs old...the manifolds were clean and in good condition when attatched to this engine and the water flows through with out any problem....the pump is a marine pump and the thermostat housing had slight corrosion but is now clean...but we still have the problem....
 
"i believe it is....i'll d

"i believe it is....i'll double check on that one but i'm pretty sure it is bi-directional....

also, do you have any ideas about the fuel problem we're having....cant really find any way to adjust the air/fuel ratio mixture....even with computer equipment....????"
 
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