2.5 L overheating above 4000

[airandsea]

Customer's boat came in with a scored #5 cyl which looked like a ring failure, but could not really tell if any prior overheats had occurred. Impeller was good and replaced anyway. Block was sleeved and a std piston (Pro cast) installed. The engine started and idled perfectly. During breakin the horn goes off above 4000 rpm. Oil was added to the fuel, all 6 plugs look good tempwise. Both heads were equally hot.
Don't know where else to look?

[Dave S]

The poppet valve could be full of salt, then it can't open. I mean inbetween the outter covers of poppet. Also check the gasket under the ss plate under the impeller some times that gasket can blow out. That will bypass water and not make pressure. I hope this helps you.

[Talon2.5]

dave made some good points there, so many people just replace the upper when its toast but leave the lower, bad move, i have seen too many warped housings upper and lower to just do an impeller, i change the entire housing upper and lower once a year after inspecting it for warpage, then later in the summer if it seems to be getting warmer i do the impeller again (after knowing the housing is still good)

the copper feed tube can get pin holes in it also ;)

[airandsea]

Thanks alot, they'll be the first 2 places I look.