overheating mercruiser

[skyhook]

the boat is a 1992 welcraft wth 5.7 260hp mercruiser with alpha 1 outdrive.
the problem is the boat overheats when you slow down from cruising speed the alarm starts going off and tempature spikes to 180 degrees. replaced impeller,an thermostat bfore season .the boat only over heats when you go from cruising speed to idle. any information would be greatly appreciated

thanks
rich

 

[Bt Doctur]

Re: overheating mercruiser

engine circ. pump?had a v6 doing the same thing. was equipped with the large water pump "7 inch,i think" for some reason.seems the water wasnt getting out of the block fast enough at off idle.installed the original smaller pully and the trouble disappeared.

 

[Bondo]

Re: overheating mercruiser

Do you go boating in Saltwater,..??....

Have the Manifolds,+ Risers ever been serviced,..??.....