Optimax 150 steady alarm at 2300 rpm

[JameyR]

Hi guys. New to the board and hoping for a vacation saving solution.

1B490525, APR 2007, 150 CXL, counter rotation with twin on ‘80 Mako CC.

Engine has started alarming with steady whistle at 2300 rpm. Will run indefinitely at 2100-2200, and alarms at 2300 even if increase in rpm is due to other engine throttle or change in trim. Reduction below 2300 stops alarm and engine runs fine.

Steady water stream at idle and higher rpm.

Just changed water pump gaskets and impeller. Also cleaned sea strainer (slightly clogged). No change.

No functioning gauges other than rpm.

I’m 2-3 weeks from appointment to get the motor scanned and by then vacation will be done.

Any suggestion? Hoping somebody can be a hero!

Thanks,

Jamey

[leonreno]

First things I would check would be thermostats and poppet valve. Could be a bad gasket in the water pump or the gasket below the base.

[SilverFox579]

First things I would check would be thermostats and poppet valve. Could be a bad gasket in the water pump or the gasket below the base.

^^^^

Did you have the alarm condition before you serviced the water pump on that engine?

On the 2.5L Optimax a full water pump service includes, at minimum, the impeller, plate, and 3 gaskets. One gasket above and one below the plate plus the one below the pump base. First thing I'd do is double check water pump work. Keep in mind, a steady tone from warning horn is a critical alarm. I would not run the engine until issue is corrected.

[JameyR]

Thanks for the responses.

I did have the alarm before the water pump change, and hoped that the water pump might fix the problem.

For the pump work I used the full set of gaskets included with the kit and replaced them in the same order as the old ones.

Don’t know if it’s relevant, but the first alarm occurrence was when maneuvering in reverse in heavy current around a crowded dock and hit high (not sure how high) rpm to avoid another boat.

Thanks,

Jamey

[JameyR]

I did not replace the gasket below the pump base. Will order and replace.

[EuropeanAM]

Could also be the shift position switch (if unplugging switch allows you to accelerate, REPLACE switch). If PCM sees a "Neutral" position, it will limit engine RPM's.

[JameyR]

Thanks for the suggestion on the shift position switch.

Is this PN 889514A01 called “switch” on throttle lever and shift shaft diagram?

Any tips on how to access and test/replace other than unplug and see if will accelerate?

Thanks for the help!

[SilverFox579]

I did not replace the gasket below the pump base. Will order and replace.

If you got the full Mercury gasket kit, the pump base gasket and o-ring were included.

[JameyR]

A bad neutral switch was the culprit. It was stuck in “plunger depressed” condition. New switch ordered for $40, replaced in short order and engine is now back to normal.

A long wait for a mechanic visit is avoided and we’re able to use the boat while still the middle of fishing and vacation season!

A huge thanks to EuropeanAM and the BBC board!

[leonreno]

Nice!

[fly by night]

Don strikes again, to the rescue!

[JameyR]

I was able to take my 14yo son,
my brother (on his bday), and my 10 yo nephew on a snapper trip yesterday to catch their limit on a beautiful day. If you wondered how this site matters... we’re proof of it! Thanks Don!