Overheated now won't crank

[rheine]

88 merc 3.0
Kids brought the boat in for a break. Would not start back up. I pulled the cover off and the motor was very hot. Had oil so I am initially guessing a stuck thermostat. Impellor and water pump were new last year.

I pulled the plugs, wouln't crank. Put some Seafoam in each hole and sat overnight. I can hear it barely moving when I try to engage the starter and a little smoke came from #1. Is there a better method to try to free this up or is it toast already?

 

[79mach1]

Re: Overheated now won't crank

its probably cooked, probably stuck the rings to the pistons or something stupid like that your better off having a mechanic look at it

 

[Don S]

Re: Overheated now won't crank

IF it seized due to the overheat, and it still won't turn with the starter with the plugs out, try this first.
Remove the outdrive, with the spark plugs still out and the alternator belt real tight, see if the engine will turn easily by turning the nut on the alternator with a wrench.
It should turn fairly easy without spark plugs.
IF it won't, then time to pull the heads and look for scored cylinders