mercury overheat

[kenner04]

I have a 04" Mercury 200hp / EFI motor that has less than 100 hours on it. recently the overheating alarm sounded as I was around 4000rpm. I checked for obstructions & also reversed vigorously and tried again. I ran the throttle up slowly & was able to maintain 3000rpm only. Anything else would sound the alarm. The water coming out of the pisser was too hot to touch. What should I look for??
Thx

 

[CharlieB]

Re: mercury overheat

First thing is to look inside that water pump. An empty plastic bag in the lake, blocking off water to the pump for even 30 seconds while under way, will melt the impeller and housing. The reversing trick sounds good, on paper, but its usually too late.

If the housing is warped, the pump MAY move enough water to cool the motor at low speeds, but once the boat begins to plane and rise, the pump rises above the waterline and begins to suck air, no longer moving enough water to cool the harder working motor, and the temps begin to climb.

A spare pump kit, alongside a spare prop, can save many weekend trips from an early (and sad) return home.