Overheat 135hp 99' Optimax-other reasons???

[barryll]

Previous link - http://forums.iboats.com/showthread.php?t=222354

I believe everything that can be checked or replaced in the cooling system has been done. I still overheat between 1800 - 4000 rpm. Can anyone think of another reason I am still overheating. Other details - 1997 Starcraft Fishmaster - Merc alum. prop 21p-14in dia.-2.0-5000rpm-39mph(gps)@WOT with (weight) full fuel (30gal), 9.9 merc pro troll, 1 aft battery, 2 troll batteries in front, 3 adults appox 620lbs. The cavitation plate and keel are in alignment. Overheat happens whether I'm slushing (what I call going just fast enough not to pound the boat in large waves - not on plane) or on plane, in that rpm range.

Could the motor be getting to lean of a mixture in that rpm range? Can this be checked? I use Merc Optimax syn blend. When powering up to plane, it has the smell of burning (or not the normal smell of a 2 stroke).
Could there be to much load on the prop/motor at that range?

Once past 4000 rpm, CHT decreases down to +/- 140 and I can run all day.

Any and all comments will be appreciated!!! This is driving me crazy(ier)

 

[Prop Buster]

Re: Overheat 135hp 99' Optimax-other reasons???

I had NUMEROUS so called experts look at my boat and comment on what they thought was my perpetual overheating problem.
I also did everything, (so I thought), to rectify the situation.
Last month I was going to replace the manifold and risers becaue of the possibel "Daming" SYNDROM which was thought to be happening.

I took off the exhaust boots connect to the cast iron pipe going back into the transom...What I found was the starboard side "shutter"...it was broken and cocked inside the tube and it didn't move freely...

This was the reason I was constantly overheating. Why my starboard side was 50 degrees hotter than my port side.

I took everything apart in that cooling system... and paid someone mucho $$$$ to do it before me....

Check those shutters..........It helped me out and I wish I knew it before ...3 yrs. ago.

Good Luck

 

[barryll]

Re: Overheat 135hp 99' Optimax-other reasons???

Shutters??? Can't find anything in the service manual about shutters. Are you referring to the exhaust ports on an I/O?

 

[j_martin]

Re: Overheat 135hp 99' Optimax-other reasons???

DURN, my BS detector just went off.

 

[Ed R]

Re: Overheat 135hp 99' Optimax-other reasons???

EDR here, that year motor had over heating problems at that only rpm,there is a water bypass kit from mercury to fix it They rechannel the water to keep it cooler at1300, 1600 rpm! contact me, Ed R.