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OMC 5.7l overheating

mell860930

mell860930

Member
So i have this new to me boat and it has a 1987 5.7l and i replaced the impeller,thermostat new plugs and had a mechanic look at timing and replaced flapper valves. When motor runs on hose it runs fine. PUt it in water and she starts heating up and will get to 190-200. Any ideas whaty might be causing this. Really dont want to take to mechanic and get hosed on a huge repair bill????
 
does it climb idling at the dock? or only when on plane?
did the mechanic retrieve the old, melted flappers?
 
It will over heat idling and out on water in all throttle ranges. He said he retrieved the flapper valves they werent completly shot or off just some what.
 
there's some talk with Cobra impellers about the impeller housing turning and restricting flow. Starting point would be taking the hose from the drive to the tstat hsg off and seeing how much water comes out towards the engine- old impeller pieces can sometimes end up in the power steering cooler.
 
hystat said:
there's some talk with Cobra impellers about the impeller housing turning and restricting flow. Starting point would be taking the hose from the drive to the tstat hsg off and seeing how much water comes out towards the engine- old impeller pieces can sometimes end up in the power steering cooler.
Click to expand...

So should I try and remove the cooler and try to blow it out with air or water?
 
First take the hose from the impeller off at the thermo housing.See if it's blocked? Then start it and see how much water is pumping?? That OK? Then the risers and manifold are probably clogged. If they are original they are probably due for a new set? Some people will tell you you can "soak" or "acid dip" them.It's a waste of $$$ Get new.
 
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