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  1. #1
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    Temp Alarm - 150 HP Optimax - 2000

    Morning. Engine Ser. No. is 0T148359. This problem has been happening for a couple of seasons. Two shops have failed to find source, my turn I guess. Oh, new impellers/water pump kits made no difference, but I'm due for one now anyway.

    After running at or near WOT for several minutes, slowing to idle will usually trigger a constant alarm and activate guardian mode. Shutting down and restarting a few times gets me through the 'no wake zone' or whatever, until I can get back to higher rpm. Always have water streaming from telltale, pressure at WOT is about 15psi, pressure at idle barely registers on guage, but I guess that's normal - a couple of psi at idle.

    The thermostats do open around 130-140 deg based on stove top test - I'll replace anyway. I'm wondering about the temp sensor and the popett. If I understand correctly, a stuck popett will result in little or no water going to block via the thermostat path. Stats are at the No. 1 and 2 cylinders. The single temp sensor is at the No. 1 cylinder. So a faulty poppet could prevent cooling water from flowing correctly at low rpm? A warm engine and reduced cooling water produces alarm at low rpm, yes?

    Regarding the popett. I read here that you have to disconnect almost all of the wiring on the right side - I see that - but what about the trim switch on the bottom cowling, which will not slide back through the bottom cowling. Do you have to cut and splice those wires after?

    Thanks.

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    #2
    I'll take a stab at this. You should read this post about dropping to idle after a hard run.

    Normal water pressure at idle should be 1 - 3 psi, WOT pressure should be 15+.

    You mention your thermostats are opening at the correct temps. What were your water temps on the water at idle? At speed?

    If you're due water pump service, I'd start there before tearing into other things. Change the pump housing and impeller, then report back with your pressure readings and temperatures.
    _______

    Phil
    '09 Hewescraft ProV
    '09 150 Optimax

  4. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #3
    Trim switch wiring has connectors that can be unplugged. DO NOT cut wires.

    If it's been more than a year on the water pump- replace.

    Most likely, your problem is caused by one of the following:

    -Torn or damaged gasket below impeller plate
    -Sticking poppet valve
    -Powerhead or Adapter Plate Gasket Leak.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
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  5. Member
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    #4
    Thank you. Did some basic troubleshooting while at idle, connected to water hose/ears. With hose valve partly open, water escaping from ears stops when engine starts. Not saying impeller doesn't need replacing, just that it is pumping water. I open hose valve some more to ensure decent water supply. In about 20 seconds, water streams from the tell tail. It doesn't get very warm. I stut down the engine after a minute or two, but let the hose run. Water continues to stream from the tell tail for nearly a minute. The longer it flows the hotter the water gets. When it stops, it stops suddenly. No alarms.

    Does that sound like a stuck poppet, or just stats opening and closing? BTW, I didn't cut any wires yet:) Appreciate your help and patience folks.

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    #5
    Running the engine on the muffs can't provide enough water to safely rev the engine to the point where water pressure opens the poppet valve. Inspection is the only way I know of to check it.
    So many honey-dos . . . . . so little motivation

  7. Member
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    #6
    Just found the strainer screen to be partially blocked, 40 percent maybe. Since that supplies water to the port fuel rail and compressor, maybe that's it. The temp sensor on the compressor could be the one alarming. Think I'll stop there and test on the water. Will let you know.

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    #7
    Your chasing your tail unless you start with a fresh pump kit. Your problems is a pressure one - the fact that water is flowing means zip. Your tell tale tells you nothing diagnostically other than the strainer (which you have cleaned) could be blocked.

    The steps -

    New pump kit - not just impeller but gaskets and metal base plate. (I had your symptoms and it was due to wear in the plate) Clean the ends of the copper water pipe while your about it - they can get crusty.

    Remove clean test thermostats - yes you've done it but even if you have replaced them check again.

    Poppet valve assembly - note here the gasket can balloon out and impede water flow in the main channel. Check poppet slides in and out freely and check for debris. May as well replace spring and diaphragm will your there - cheap parts. Poppet can only be tested on water.

    Do each thing at a time and note any changes - do you have a temp and water pressure gauge?

    You'll get there but it has to be logical elimination.

    Q.

  9. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #8
    Quote Originally Posted by olemon View Post
    Just found the strainer screen to be partially blocked, 40 percent maybe. Since that supplies water to the port fuel rail and compressor, maybe that's it. The temp sensor on the compressor could be the one alarming. Think I'll stop there and test on the water. Will let you know.
    Running on hose with water supply only partially on is not a good idea. You can literally be starving the water pump of proper cooling media, and INDUCING a failed pump.

    Don't rev the engine unless it's IN THE WATER, IN GEAR, and GOING SOMEWHERE.

    Cleaning the strainer should be part of your regular annual maintnenace. Glad to hear you got it cleaned out.

    Now time to back up to the FIRST STEP in ANY COOLING SYSTEM PROBLEM: Always, ALWAYS start at the SOURCE: The Water Pump.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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  10. Member
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    #9
    Problem solved. Apparently that strainer was clogged just enough to reduce cooling water flow and activate alarm. Finally had a chance to test on the water today and could not trigger a high temp alarm. I did notice that water pressure at idle barely reigstered, same as before, but at just a few rpms above idle, water pressure increased to about 5psi - more than before:)

    I still need to change water pump since it's been a year, but as Don said, I need to check the strainer regularly as well!

  11. Member
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    #10
    Where is the strainer screen located? I have an 03' opti 150 that I just changed the impeller on and I still have a problem with an overheat alarm and no throttle response?

  12. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #11
    Strainer is located in the PORT side of the upper exhaust plate (adapter plate). Looks like a "nipple" from the outside... once removed with a socket, you'll see the strainer (part of the "nipple").

    You can actually follow the water supply line back from the air compressor (likely routed through the fuel rail, and then back to the strainer... the water supply POINT on the engine for the air compressor). Compressor water OUTLET hose routes to the telltale fitting.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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  13. Member
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    #12
    Quote Originally Posted by Mpierce1128 View Post
    Where is the strainer screen located? I have an 03' opti 150 that I just changed the impeller on and I still have a problem with an overheat alarm and no throttle response?
    Pictures here - COMPRESSOR
    _______

    Phil
    '09 Hewescraft ProV
    '09 150 Optimax