merc 1150 over heats when driving fast

[phatmanmike]

1976 merc 1150 I6. <br />installed new water pump kit, not just impellar, in april along with carb & fuel pump rebuilds. and tuneup. when at idle or slow cruise, all is fine, pumps nice stream of water and motor is not TOO hot to touch.<br /><br />but when going fast it shoots steam and motor gets reall hot to touch, but as soon as i slow down, motor pees again.<br /><br />cav plate is about 3/8 inch above the keel of boat. boat is 16 foot center console. motor was on a 1960 glasspar last week, and was doing same thing there......<br /><br />am i going too fast to pick up enough water? any ideas?

 

[medburd]

Re: merc 1150 over heats when driving fast

Curious?? does it do it in Neutral when you rev it up?

 

[phatmanmike]

Re: merc 1150 over heats when driving fast

dealer suggested exhaust gas may be getting in water jacket some where/how. when at idle, its not enough top notice, but at high speeds, it overpowers the water pressure... im looking into this

 

[Barnacle_Bill]

Re: merc 1150 over heats when driving fast

If that was happening on my 83 150, I would check the poppet valve, but I don't know if your's has one or not. Worth looking into.

 

[Clams Canino]

Re: merc 1150 over heats when driving fast

I'd guess an exhaust plate issue - ASSUMING that the pump is indeed getting water up on plane. Is this a new problem or a new install?

 

[phatmanmike]

Re: merc 1150 over heats when driving fast

this is a new motor to me. had been sitting for 20 years when i got it. the cav plate seems to be in the ideal location, and there is no blockage of anykind for the water pickup. i am gonna try the exhaust pleat idea.<br /><br />does anybody have a parts blow up of this motor showing the water passages? please email if you do, i will pay pal you a dollar for it, really

 

[Hooty]

Re: merc 1150 over heats when driving fast

A water pressure gauge would be handy.<br /><br />c/6<br />Hooty