mercury 2 stroke - overheating problem

[Pete L]

I have a 2000 90hp 3 cylinder 2 stroke mercury.
Took the boat out today from Trafalgar Wharf. Started no problem, idled fine, good tell-tale, plenty of oil, ran out into Pompey harbour at low revs & 10 knots for about 15 minutes. Opened her up to about 1/3 revs and immediately the overheat alarm came on. Cut back to idle and alarm went off almost immediately. Repeated the exercise twice more with same results (still had a good tell-tale). On the third occasion decided to try opening the throttle further to check if it was a faulty alarm. Tell-tale stuttered then stopped and smoke started coming from engine. Shut engine off for a few minutes then restarted no problem and idled back in. No apparent blockage to water intake. Any of you more experienced engineering types have any ideas where to start? (Water pump failing perhaps?)

All help gratefully received
Cheers
Pete

[Nos4r2]

Start by looking at the impeller. You may find it's breaking up and blocking the cooling system.

[Turbodiesel]

Yeap, you bet start with the water pump.

[Pete L]

thanks guys - sounds like what I expected - least its a simple task to replace