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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10621
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1995 115 Yamaha outboard. Impeller was changed last

Customer Question

I have a 1995 115 Yamaha outboard. Impeller was changed last year. When I run the engine about 2 minutes, the engine High temp alarm sounds. It is a steady alarm, not intermitant.
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. My name is***** you replace the thermostats also when you did the water pump?
Customer: replied 1 year ago.
Don't know, had a boat mechanic do it, guess I'll have to ask him.
Expert:  Tan replied 1 year ago.
Ok there are 3 components in the cooling system that control temp. The water pump supplies the water then the thermostats control engine temp at low rpms and the pressure relief valve control water flow at higher rpms. Both regulate the flow of water from the water pump. If the engine is over heat at low rpms the thermostats are the cause after the water pump. Since the pump is been replaced recently that leaves thermostats and pressure relief valve. If the engine is over heating at high rpms the pressure relief valve is the cause. So I would replace the thermostats and pressure relief valve depending on when the engine is over heating. I always do the pump, thermostats and pressure relief valve all at the same time to eliminate problem for the customer. Post back with questions and concerns. Thank you.........Tan
Customer: replied 1 year ago.
Sounds like pressure relief valve as it happens after running at high RPM, not at idle. Maybe I can check low RPM with Water hose clamp attachment and idle for a while?
Customer: replied 1 year ago.
Where is the pressure relief valve located?
Expert:  Tan replied 1 year ago.
The pressure relief valve # ***** 44, 45, & 46 is in the back of the motor where the hose attaches to the exhaust cover plate.http://www.boats.net/parts/search/Yamaha/Outboard/1995/115TLRT/CYLINDER%20CRANKCASE/parts.html
Expert:  Tan replied 1 year ago.
The pressure relief valve open due to water pressure. If the valve doesn't open due to corrosion the engine will over heat.
Customer: replied 1 year ago.
So garden hose attachment probably would not test anything as it probably has too much pressure.
Expert:  Tan replied 1 year ago.
The thermostat will work on a hose but not the pressure relief valve. Thermostats open due to temp and the pressure relief valve open due to pressure. The hose will not produce enough pressure for the relief valve. I would just remove the pressure relief valve cover and all the components and check for corrosion. If it is really corroded it will restrict the water flow and cause over heating.
Customer: replied 1 year ago.
Looks like something I could change myself. I am fairly mechanically inclined.
Expert:  Tan replied 1 year ago.
Absolutely it is just 2 screws. Inspecting the components and replacing any bad looking or coroded parts. If this all looks good then we have a more serious issue.
Customer: replied 1 year ago.
Used to use the engine in salt water, not any more as I live in north Idaho. Could be some salt corrosion, I'll check it out tonight after work. Thanks
Expert:  Tan replied 1 year ago.
Ok great. Your welcome.....Thank you.....Tan Post back if you need further assistance.The questions stays open even after you have positively rated. So post back if you need further assistance. Thank you...Tan
Customer: replied 1 year ago.
Will do, have a good day.
Expert:  Tan replied 1 year ago.
You do the same..........Thank you....Tan

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