Mercury Optimax?

[randallt]

I have a 135 Opti on the back of my Lund Fisherman. When I am cruising around 5 - 10 mph (not on plane of course) the engine runs hot, occassionally setting off the alarm, so 165 and up. As soon as I pop up on plane it goes down to 100 or so. I am guessing this is a cavitation issue as it happens more in rough water than calm. My question is do these motors have impellers and water pumps and could either be changed to eliminate this? Could this be a sign that one is going bad? Should I not worry and just live with it?

[ChuckN]

Strange.

I would guess it's time for a new water pump. How old is the motor? Regardless, there are many ways an impeller can wear out or get damaged.

Typically, if the impeller is bad engines will get hot at idle because the impeller is not forcing enough water upwards to the powerhead to properly cool the engine. When at higher RPMs, there can be sufficient water pressure.

I would say every 2-3 years the impeller should be replaced. It's not a very difficult job. A water pump kit from Mercury is around $50.

[mnfishman]

How is the stream of water coming out of the back of the motor? Is is strong or just dripping out? How long has it been since you last had the water pump replaced? Water pump replacement usually needs to be done about every 3 years or so depending upon how often you run the motor.

I would get it checked out right away before you melt down the motor.

[randallt]

Water comes out strong. Impeller has never been changed, motor is 4 years old and has 105 hours on it. Sounds like I will take it in and have it replaced.

[tuffyboone]

Don't be surprised if the mechanic recommends a new thermostat. A member of my old club had issues with an Optimax and it all boiled down to the thermostat design. They tend to get clogged with debris pretty easily and his mechanic showed him how to remove and clean his to reduce future problems. He always had plenty of water through the system too. Just something else to ask them about.

[zepman]

I had the same problem as you described and it was the thermostat. Quick and easy fix although it did take a trip to the shop to get it done. Thinking about it more--mine was actually running too cool and wasn't properly warming up. Either way check thermo first.

[hitthebricks]

A thermostat went out on my 200 Opti this spring and cost me about $275 to replace. I would like to know how to remove and clean it myself so maybe I wont have bring it in if it happens again. HTB