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  1. #1
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    Default Can overheating crack block???

    OK, I just took my boat to be winterized but was told by the mechanic the block has an external crack - maybe one on each side, I was so depressed i forgot, I'm going to see it today. Anyways, I am now trying to figure out what caused this. He assumed it was from improper winterizing last season. however, to make a long story short, I purchased this engine used last year so it was installed this past Spring. The relatively inexperienced guy i had install it says it was not cracked at the time (he didn't sell it to me and is a friend so he wasn't screwing me).

    Mercruiser 350 Mag engine. Fresh water only. The engine was performing fine all season. I did watch it run early in the season and the water pump was leaking a bit - replaced by the mechanic then no leaks that I or he ever saw. I am fairly sure no water in oil, but I'll find out more on this today. I don't recall watching it run uncovered after the following problem happened. I do not think my temp gauge works properly.

    I'm wondering if it cracked this boating season when my outdrive oil leaked out causing my upper gears to fry. I was out on the lake when this happened, but I didn't know what the issue was, only that the prop wouldn't turn. So I tried a few times to get it going, meaning I ran the engine for a while (no idea how long - maybe too long). I assume this condition causes the impeller to not function so I was likely running without cooling water. Could this cause a cracked block???

    Aside from improper winterizing, what else can cause the block to crack?

  2. #2
    Commander 45Auto's Avatar
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    Default Re: Can overheating crack block???

    I've heard about car engine blocks that cracked from being overheated then having water added to them while they were still hot. Was always told NEVER to add water to an overheated engine, let it cool down first. Adding the cold water cools the metal down unequally (it cools the thin outer wall - the water jacket - quickly, but boils off before the internals can cool off so the water jacket cracks). Could it possibly be something similar on yours, the engine got hot with no water in it, then the impeller gave it a shot of cold water before it crapped out?
    Any opinions expressed above are worth exactly what you paid for them!

  3. #3
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    Default Re: Can overheating crack block???

    OK, went to mechanic's shop and saw the cracks. They are about 1 1/2", very thin, just above the drain plugs on both sides. The mechanic seems pretty sure they were caused by freeze damage last winter. hesays they barely trickle a leak and may not have been easily seen until the rusted up a bit. Doesn't matter much anyhow as now I need to fix it.

    Based on the age of the boat and the otherwise good engine he said he'd grind/sand then patch with Marine tex if he were me. I tend to agree as i do not want to throw lots more money at it. i know a block isn't too expensive, but I have neither the time, facility NOR ability to do it myself so the labor cost of a new block would kill me.

    Mechanic said he prefers Marine Tex to JB Weld but also said he hadn't done this often himself, more word of mouth.

    I'll start a new thread to get ideas on what product to try, as i know several here have opinions on this.

  4. #4
    Commander 45Auto's Avatar
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    Default Re: Can overheating crack block???

    Sorry to hear it's really cracked. Good luck with the fix, no matter which way you go!
    Any opinions expressed above are worth exactly what you paid for them!

  5. #5
    Fleet Admiral jerryjerry05's Avatar
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    Default Re: Can overheating crack block???

    Overheating can hurt the heads,usuall not the block.If they are barley leaking why worry? If the leak into the oil thats a different problem.If it was a closed system Bars leak would help but an open system will need some other treatment.I've heard dustless balck pepper helps small leaks,figuring out how to put it in the block might be tricky.Jerry

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