115 HP Mariner Overtemperature alarm at 5000RPMS

[raggy4u2]

Motor is 115 HP Mariner ELPTO-1995 on a Pro-gator boat. Recently purchased this rig from a friend. Boat, motor and trailer we stored in a garage for last 12 years. Setup is original from factory. As a precaution I changed water pump impeller and plugs before trying to run it. I then tried to run motor on muffs. It WOULD NOT pump water with muffs. Did tons of research and decided to take it to the lake and try it. Pumped water great at about 10 PSI at idle. After seeing it pump water I decided to run it on the lake. When running 4000-4200 rpms and water pressure is right at 20 psi and runs great. Then when you open it up to full throttle at around 5000-5200 rpms and with 25-28 psi on water pressure gauge for about 30 seconds and the high temp alarm comes on. I can run it back to neutral for a few seconds and horn turns off. Since then, I have changed thermostat, poppet valve, water temp sensor and flushed the motor. Same problem happening afterwards. I'm at a loss for what to do next. Any help is appreciated.

 

[cyclops222]

YOu have ...PARTIAL BLOCKAGES... In the 1 or more places of the ENTIRE .cooling system........... Good luck on finding 1 or SEVERAL smaller blockages. Decades ago we had many motors having same problem as yours.
Bad news was Zebra Mussels Growing the the coolant passages. Took years in some boats.
You have to get lucky If it is Zebras. Neighbor had them holding QPEN his BELOW the surface Bilge Flapper Valves. WE got to his boat Just as the water was coming over the deck. O B saved inboard engine disaster.

 

[raggy4u2]

Thank you for the reply. I'll look into it the next time I take everything back apart. Everything I read takes me back to poppet valve.

 

[Chris1956]

You need to consult a real expert like Fazt, as that WOT water pressure sounds high to me. It is much higher than my Merc V6 or my Merc IL6, which are different from your motor.

 

[raggy4u2]

You need to consult a real expert like Fazt, as that WOT water pressure sounds high to me. It is much higher than my Merc V6 or my Merc IL6, which are different from your motor.

Thanks Chris. I posted this on another forum as well. I think he answered on it. He told me to look at poppet valve again.

 

[cyclops222]

I webbed the Poppet Valve function. All agreed high rpm overheating SHOULD be the Poppet valve.

 

[raggy4u2]

I ordered ANOTHER OEM poppet valve assembly this morning. On another thread I was reading it could be grommet where exhaust manifold meets water tube causing a restriction