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Thread: 75 hp Optimax

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    Default 75 hp Optimax


    2008 Mercury Optimax. Cranked it today and water guage was showing 14psi at idle. Normally it sits between 5-7. And goes to 12 at 4900rpm. Any suggestions on where I look first. I think the impeller is not 2 years old and is ran really often.

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    run a thin wire up the pee hole, sometimes mud dabbers get in there. Saying this because you say normal is 5-7 and now running 14 sounds like it's stopped up somewhere. That's the first place to start
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    Thin wire it is thanks

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    If discharge hole is obstructed it may be giving you a false reading at the gauge.



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    long crappy story on water line(broke the nipple off in the fuel rail water jacket). New line and rerouted to take a bend out that I thought might be causing restrictions. Still reading high. Would like input on next step please.

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    You could possibly have a piece of your impellor broke off and obstructing a water jacket or some other obstruction that could cause a high reading.
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    I have started the engine four times after pulling it out the river during the cold season. In attempt to blow water out since it's been a cooler winter. Only so many froze water lines I could stand.

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    Think first thing I would do is disconnect gauge line at motor, crank and see if it’s actually pushing that kind of water out. At 5-6 shouldn’t be that much, at 15 it would be peeing a pretty significant amount out. That way maybe you could eliminate a gauge problem. It’s hard for me to believe that pump would put out 15 psi at idle unless something after that pressure port is completely plugged.
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    Volume of water looks good. Is there a way that gauge can lose calibration.

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    I would say if it was sitting out where it could possibly froze it could affect internals of gauge. Those standard gauges are pretty inexpensive built so yes it could go bad.
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