115 Optimax Pro XS operating temp question

[jokerjp]

I recently installed a merc monitor and on my first trip to the lake I became concerned with the coolant temperature reading. I let the engine warm up to 120 degrees before slowly taking off, shortly after I got on plane the temperature dropped rapidly down to approximately 75 degrees. Seemed like a severe temperature drop to me and I wanted to know the expected normal operating temp range. When I slow back to idle the temp will raise up to about a max of 140 degrees and drop quickly again anytime I get on plane.....not sure if i should be concerned or not.

Thanks in advance!

1. Engine size 115ProXs
2. Engine serial number - 1B850628

[EuropeanAM]

THANK YOU for providing your serial number.

What you're experiencing is perfectly normal.

The thermostat controls engine temperature at IDLE SPEED. Once you begin to accelerate (by approximately 2000 RPM's), the POPPET VALVE is open, allowing a FULL FLOW of water through the engine block (essentially, the thermostat is just along for the ride at higher RPM's).

Hence, on-plane temps will vary immensely, based on multiple factors (including load, RPM, and lake water temperature).

When you return to idle, the poppet valve closes, and thermostat is again in control of engine temperature.

[jokerjp]

Thanks Don! I was very concerned unnecessarily and I sincerely appreciate the time you take to answer questions for us here on BBC.

[randymarshall]

So if I am getting 75 at wide open and 140 - 160 at idle, I need a new impeller? How do i disconnect the tube to the pitot when pulling the lower unit?

[randymarshall]

2006 150 optimax

[EuropeanAM]

2006 150 optimax

Randy:

Welcome to BBC!

Best to open your own thread, for questions related to YOUR engine (be sure to give all specifics, including engine serial number).

This helps to prevent confusion with the OP (original poster's) engine... and avoids post hi-jacking.