water temperature concerns

[jay's snake]

Optimax 150 serial# 1B434225

For some reason, the water temperature in my Optimax seems to drop rapidly as soon as I go faster than idle speed.
Here are some numbers I captured today.

engine speed	water pressure (lbs)	engine temperature
idle	3.9	145
1000	7.1	134
1800	8.4	99

I think the thermostats open at 143 so the idle temperature is about right (correct me if I'm wrong).
What concerns me is the way the temperature drops as the RPM increases.
I have read that the engine needs to be above 120 to be safe to run at speed.
I replaced the water pump about 53 hrs ago. Does this sound like a thermostat or a poppet valve problem?
The engine is running fine and I don't have any alarms or codes stored.
Air temperature was about 68 today and the water temperature was about 60 degrees.
The readings were retrieved via the Vesselview mobile app.

[EuropeanAM]

Very simple. Working AS DESIGNED.

Thermostats control water flow AT IDLE. As soon as WP reaches approximately 6 psi, the poppet valve begins to open and permits a straight-through flow of water to keep the engine cool. The faster you run the cooler it gets (especially in cold water temps).

Return to idle and temps should stabilize within 10 degrees of thermostatic temp.

[jay's snake]

That's sure good to hear!
After I made the posting, I found all the other threads and read through them all and started to realize that mine is working normally.
It still seems to me that the temperature could be more controlled above idle like a car is. I would think that the engine would be happier with more consistent temperature control.
Anyway, thanks for confirming that mine is normal. I've got plenty of other things around here to fix!

[leonreno]

The temp is not the motor temp but the water temp, the motor components are warmer than the water temp. But also realize cars don’t stay at higher rpms like an outboard. Your outboard, when on plane will stay above 3500 rpms and upto 6000 rpms, and that’s its normal operating range where a car rarely sees more than 3000 rpms except for short durations of acceleration. Plus cars don’t use raw water to cool off, they have a closed system where as it would be difficult to regulate water temps at higher rpms on an outboard like a car because it would be difficult to fit a radiator.

[SilverFox579]

^^+1^^

Big difference between an open vs closed cooling system.

The 120deg reference is minimum engine temp prior to accelerating after initial start. Fail to heed that and you risk a cold seize event on cyl #6.

[JOE54]

^^^^^^+2

[jay's snake]

Thanks everyone. I appreciate your help!!