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  1. #1
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    1998 225 Merc Motor HELP!!

    We took our boat out a few weeks ago for the first time this year after replacing the lower unit and noticed the motor wasn't running right after about 10 minutes of idling we decided to just drop the trolling motor and fish.. trolling motor wasn't running right (it's brand new) and about 5 minutes later the battery blew up!! We called it a day and went to plane the boat off to get back to the dock and the motor had lost alot of its power. We loaded the boat back up and took it to a mechanic...
    1st mechanic said compression was 125 on all cylinders but that gas was leaking from both sides of the motor at an idle. He said it seemed to him like the bolts had backed out causing the issue. He didn't have time to work on it so we took it to another mechanic....
    2nd mechanic said compression was different on all cylinders ranging between 105-120. He also said we needed to rebuild/bore the engine and that 2 spark plugs weren't firing and quoted us about 5k for the work..

    I said all of this to ask if anyone else has had the issue and if so what did you do to fix it? We've been told so many different things and a boat motor is one thing we don't know alot about. When we had a new power head put on (about 6 yrs ago) should the bolts have had lock-tite on them to keep them from backing out?? We need any advice we can get!

  2. #2
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    Sounds like you have more than one problem and they could be difficult to sort out over the internet. I think you need a good marine mechanic that you can trust. I know that personally I would be skeptical about taking your boat in knowing that it has already been in to two different mechanics.

    First of all, more information is needed. How many batteries are on your boat and how are they wired? Typically a trolling motor is on a separate bank of batteries from the starting motor and may be 12, 24, or 36v.

    Gas leaking from where? What bolts backed ou? This has nothing to do with the batteries...

    Compression numbers should be independently verified. You can get a compression tester very inexpesively and do this yourself (with proper guidance of course).

    Spark plugs not firing could be related to the electrical incident, but I’m still not clear exactly what happened there.

    With a battery exploding there could be all kinds of electrical problems that need to be repaired.

    First the cause needs to be identified and repaired. Second, any “collateral damage” needs to be addressed. I would prioritize this over any possible mechanical issues...

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  4. #3
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    How many volts is your new trolling motor? Can you post a picture of your batteries and how you have/had them wired?

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    Nitro_Rat I will answer your questions as soon as my husband calls back and tells me exactly where the gas is leaking from and what bolts backed out...

    Bullet123 - the trolling motor is a 24V and is on a seperat e battery from the cranking battery. We have 3 batteries on our boat. I can take pictures as soon as we pick it up today.

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  8. #5
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    Is this the promax you were trying to sell a few months ago?

  9. #6
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    Yes, bullet123... We ended up getting a great deal on the exact lower unit we had on it, $350 so we decided to keep it since the last time it was used there was nothing wrong with the motor itself and now we have this issue!! My husband is honestly ready to part out what can be and buy a brand new motor but I'm not ready to drop 15-20k into a motor, controls and rigging it up!

  10. #7
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    225 promax is as good as it gets in my book. Smart move to keep it IMO.

    Pics of batteries and wiring will be a good place to start.

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  12. #8
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    Nitro_Rat, the bolts that backed out are the bolts that connect the 2 block halves together and that is also where the gas is leaking from...

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    Can you post a pic of the bolts on the block and front half you are speaking of? The trolling motor should have an inline breaker on the hot wire coming from the battery (40-50 amp) to prevent damage to trolling motor.

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    Quote Originally Posted by bullet123 View Post
    Can you post a pic of the bolts on the block and front half you are speaking of? The trolling motor should have an inline breaker on the hot wire coming from the battery (40-50 amp) to prevent damage to trolling motor.
    Also was the replacement powerhead from Merc? Merc dealer did the work? Or was it an independent shop rebuild?

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    A bad voltage regulator or a bad short could cause the battery to explode. Was it the cranking battery that exploded? What kind of battery was it?

  16. #12
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    We are going to pick the boat up in about 3 hours and I'll get pictures of all of it.

    The battery that exploded was the trolling motor battery and it sounded like a shot gun went off, it blew the box lid up that the batteries are in and blew the entire top off the battery! I'll post pictures of the battery once we get it back.

    The powerhead came from Merc but it was a marine mechanic who installed it and did the work. We have the receipt from where the mechanic purchased it but ill have to ask my husband where it is.

  17. #13
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    Since it was the trolling motor battery that exploded, I would think it maybe had a dead cell. It also could have had a low water level. A bad charger can sometimes contribute to a situation like this. The trolling batteries should be on a separate circuit from the starting batteries. This would lead me to believe that your trolling motor problems are unrelated to your engine problems.

    There is a possibility that the problems could be related if both the starting battery and the trolling batteries are connected to the same faulty multiple bank battery charger...

  18. #14
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    My husband just said he believes it was a low water level that caused the battery to explode.

    He also just said that the bolts they are thinking backed off are inside the 2 halves.. 1 guy told him he would have to break down the entire motor to get to them and another guy told him there's a cover he can remove and should give him enough access to check if the bolts are loose..
    Do you know what would cause those bolts to loosen and let the gas leak from there? Are those bolts supposed to have lock tite on them when they are torqued to specs?

  19. #15
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    The bolts you are referring to can't be seen unless you take the intake off. I don't know how the mechanic came to that conclusion. Yes, red Loctite on every bolt except reeds, use blue.

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