Optimax Overheating


I have a Baycraft 18` with a 135  Optimax. Motor is a 98 with 500 hrs. The Prop is a 4 blade, 21 pitch. I installed a jackplate and almost immediately started having heat issues. I have replaced the impellor, 2 new thermostats, (143 deg) I have even installed scoops, (low water p/u). Finally, I lowered the motor on the jackplate as far as I could.

By finally lowering the motor I can actually get up on plane. Anything over 4000 rpm the overheat light comes on, but the alarm does not sound. This concerns me. The motor as well as I can see is not salted. The thermostats were a little corroded. But, were also original.

Is there anything else that I can do to alleviate this issue??? I am dumbfounded, and cannot afford to take it to a shop and just start tearing it down. 

Could you please give me some insight??


Sounds as though you are running too high on a boat that never was designed for a Jackplate. The prop shaft should be 4-5 below the keel. Any higher on that style of boat is wasting thrust. 




Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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