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Jason, Boat and Mechanical Expert
Category: Boat
Satisfied Customers: 210
Experience:  10 yrs. running and working at my boat dealership.
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i have a 2004 Mercury optimax -135 hp. The motor at idle speed

Customer Question

i have a 2004 Mercury optimax -135 hp. The motor at idle speed will occasionally trigger the heat alarm. I have watched the digital temp rise rapidly then fall rapidly. I can abort thr rise with engine acceleration. What does this suggest? Thermosat, impellar?
Submitted: 7 years ago.
Category: Boat
Expert:  Jason replied 7 years ago.
These engines are very tempermental when it comes to the cooling system. I have a pair, and deal with it frequently. The first thing to do is change the impeller. I would recommend doing this annually on this motor. Two other items that require maintenance on the cooling system are the thermostats and the poppet valves. If you have never changed the poppet valves I would have them changed, especially if used in saltwater. I cannot recall when the new thermostats were put into service as I am home right now, but there have been two different ones for these motors. The newest version runs at a higher temp to allow better fuel combustion. This unfortunately amplifies any issue with the cooling system. If using in saltwater, I recommend flushing the motor with Salt-X. I have been using this product, and have been running a little cooler as of late because it helps to assure the water passages are clear of any corrosion. If this answers your question, please hit the accept button. This will not prevent you from asking follow up questions. Positive feedback and bonuses are always appreciated. Thanks for using Just Answer! Jason
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Customer: replied 7 years ago.
Thanks i will sart with those issues.
Expert:  Jason replied 7 years ago.
Sounds good. Make sure you start with the impeller.

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