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  1. #1
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    Mercury 250xs power head replacements why?

    I see alot of 250xs for sale and more than a few that say X amount of hours on new power Head? Why do these motors need new power heads so much and after replaced are they more reliable? I would think you should be able to go 2000 hrs with these motors with gas and oil. Whats up with this any one care to elaborate?

  2. #2
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    250xs and 250pro xs is a very popular for bass boat owners. The problem with blown powerheads is that alot of them trolling around with motors which is not good for motor. Mercury loves to be run hard one mechanic told me. Another problem is the octane and useage. What i mean by this is guys will run boat and let same fuel sit for weeks losing octane rating which will cause detonation on next trip out. 9 out of 10 if a 250 is been sold its from a bass boat and minute warranty is up or mercury has a sale they buy a new one.
    Last edited by 2jz; 03-23-2017 at 08:57 AM.

  3. #3
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    Most Optimax powerhead failures are caused by "cold seize". If the motor is not sufficiently warmed up before takeoff, then the piston will expand before the cylinder and then seize in the cylinder. This can also happen if a piece of debris is in one of the thermostats which will not allow for proper warm up of the cylinders before takeoff. I would not run a Optimax without some type of smartcraft gauge. A smart craft gauge will allow the user to watch the water temperature rise to about 130 degrees and then drop when the thermostats open. When they open, the engine is warmed up and you are safe to take off. If it never gets to temp, then you have debris in one of the thermostats. Direct injector failures and compressor failures can also cause engine failure, but don't always cause an engine failure if you shut down the engine and idle back to the ramp.

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  5. #4
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    Agree, to not have a simple Smartcraft gauge is crazy. I'd also suspect that the bass guys run in even colder water than most based on year round running so you are correct on cold seize. Five minutes of proper warm up matters a lot.

  6. #5
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    Down side to the smart craft ga is that they take an average reading of 3 temp senders and show that. You could have a t-stat stuck open and still not know it. With all the tech involved with these gauges, we should be able to monitor any of the 3 temp senders on the motor independently. I suspect this may have something to do with the cold seize issue some have.

  7. #6
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    Quote Originally Posted by XstreamVking View Post
    Down side to the smart craft ga is that they take an average reading of 3 temp senders and show that. You could have a t-stat stuck open and still not know it. With all the tech involved with these gauges, we should be able to monitor any of the 3 temp senders on the motor independently. I suspect this may have something to do with the cold seize issue some have.
    Its would be nice to read all 3 temps independently on the smartcraft gauge but that is not practical for 99.9% of the people out there. It is pretty obvious when you have a stuck thermostat as the water temp will never get up to 130 and then drop (seen it many times). The newer gauges will also give you a warning. It will let you run...but will usually give a couple of beeps when you take off. Overall these motor are still better than the old EFI motors and their competition.

  8. #7
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    I have 3 optl's on 3 boats, and have a seperate temp sender in each head. One gauge and a either/or switch. Have seen a problem with one side being too hot or cold way before the smart craft ga gave any real indication. Never had an alarm go off or a warning show either. jm2cts And I agree they are great motors.

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  10. #8
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    Quote Originally Posted by XstreamVking View Post
    I have 3 optl's on 3 boats, and have a seperate temp sender in each head. One gauge and a either/or switch. Have seen a problem with one side being too hot or cold way before the smart craft ga gave any real indication. Never had an alarm go off or a warning show either. jm2cts And I agree they are great motors.

  11. #9
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    I run twin 225 optimax with temp sensor on port heads no smartcraft. Great motors easy on gas and can run 87 octane. I really dont look at them as 2stroke motor because they burn so much cleaner then efi and carb.

  12. #10
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    I do not own a low emission motor,but I was taught a long time ago to let the engine come up to temp or at least stabilize a little and get the oli circulating good be fore getting going.this applies to all 4 strokes.why does most guys get in the boat cast off and haul A$$.didn`t get up in time?i agree with the cold seize theory 100%

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  14. #11
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    They will get a new Motor if the motor let go , from the support truck . There minds on the fishing spot ? At least that how it use to be . So much change these day's.

  15. #12
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    I always idle until water temp reaches 130 in all my boats. I also let my cars, trucks , atvs, and any other motor warm up before I run them even up to normal operating speed.

    The keys to long motor life are
    warm them up before heavy throttle,
    do not let a motor get hot,
    run the right fuel with no restriction (no ethanol in any thing except late model cars and trucks), change and use the right oil,
    and on land ,change the air filter.

    If you do that, you will get the expected life of the motor
    If you don’t follow these simple rules, you will have much shorter motor life and most likely have a catastrophic failure.

  16. #13
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    Quote Originally Posted by whipper View Post
    I would think you should be able to go 2000 hrs with these motors with gas and oil
    They are supposedly designed for "high hundreds" of hours.
    Markus' Performance Boating Links:
    www.toastedmarshmallow.com/performance

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  18. #14
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    Me too

    Quote Originally Posted by J.R. View Post
    I do not own a low emission motor,but I was taught a long time ago to let the engine come up to temp or at least stabilize a little and get the oli circulating good be fore getting going.this applies to all 4 strokes.why does most guys get in the boat cast off and haul A$$.didn`t get up in time?i agree with the cold seize theory 100%
    Totally agree.I run my 250 efi hard on the Paramount for 13 years with no problems.Best motor I ever owned.j

  19. #15
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    Warm up is key..

    4-16-2014. 25 years old today... the fishin boat doesnt look to bad for a classic does she


    things that were are no longer as they are today...

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