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  1. #1
    Cadet
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    Default Freeze plug replacement

    I have a '96 5.0 volvo i/o, and did not drian the water from the engine this winter. I discovered that 4 of the 6 freeze plugs had popped out. I have replaced these as best i could, but they are painfully difficult to get to (engine mount brackets in the way), so they are not pressed in well. I have started the engine and it sounds ok.

    Question 1: Is there a special tool to press these in? Can a shop do this for me?

    Question 2: Is the casing behind the freeze plugs pressurized? Are the plugs trying to be pushed out?

    Question 3: What are the tell-tell signs if there was more freeze damage besides the plugs? What would i look for?

  2. #2
    Petty Officer 1st Class 88wellcraft's Avatar
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    Default Re: Freeze plug replacement

    I read somewhere on here that they are actually casting holes and not meant for freeze protection. I didn't properly drain my block one season and started it up in the summertime and had water pouring out the side of my block. looked in the bilge and there was the plug. cleaned the hole and the plug with some sandpaper and tapped it back in and i was good to go.

    that being said.....if you are leaking any water or if you start having overheating issues....there are issues. I would check your oil and run it on muffs for a while and then check your oil again. All the while checking for any water obviously leaking from anywhere.

  3. #3
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    Default Re: Freeze plug replacement

    Thanks. I have tried to press them back in and have run the engine for about 25 minutes without any obvious problems. I am worried about the brass plugs not holding since i wasn't able to do a proper press fit, but i have since bought rubber expansion plugs as a backup should they pop out during operation. I still don't have a good idea of what to look for other than milky oil (meaning water is getting into a cracked block). Any other tell-tell signs?

  4. #4
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Freeze plug replacement

    They are called core plugs used in the casting process, they are not "Freeze Plugs" nor do they prevent freeze damage to the engine. In fact, they are part of the damage.
    They are also not reusable. they might stick in there a bit while on muffs, but they won't last long out on the water.
    Don S.


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    Only forum/moderator issues will be answered in PM's.

  5. #5
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    Default Re: Freeze plug replacement

    Understand. So are you saying that there is pressure behind these plugs that wants to push them out, or don't you know?

  6. #6
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Freeze plug replacement

    So are you saying that there is pressure behind these plugs that wants to push them out, or don't you know?
    There is some pressure, not a lot, and yes I know what I am talking about.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  7. #7
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    Default Re: Freeze plug replacement

    you can buy new plugs that u push in they have a rubber seal on them and there is a nut on it you put the plug in tighten the nut to make it tight in the hole and you will be good to go if there are no other problems with the moter do to freezing

  8. #8
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    Default Re: Freeze plug replacement

    I have found the rubber expansion plugs you are speaking of. The question now is do i pop out the brass plugs i've already semi-pressed back in and use the rubber plugs, or do i take my chances that the brass plugs will hold. My biggest fear is that they blow when out when on the lake and i either can't cool down the engine and/or can't prevent the leak and sink the bloody boat. Aargh!

  9. #9
    Lieutenant Commander
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    Default Re: Freeze plug replacement

    One time I had to replace a Mercruiser short block due to a bad head gasket--pitting the space between cylinders. I had to wait over 6 months for an engine, as Mercury didn't have any engines warehoused. Mercury and other boat manufacturers only rent out the GM engine factory something like one per year to cast engines to their specifications. The metallurgy and motor mounts are different on marine engines. Mercury said that seldom does a customer wear out a car based engine--that the vast majority of replacement engines is due to freezing.

    I don't have any idea of the space you're working in. You might could pierce the brass plugs if you had room to get a hammer in there. Then, pry them out with a screwdriver. I'm not familiar with the rubber replacement plugs--and if using them will work. I personally would probably pull the engine and fix it right if you cannot replace the brass plugs due to a lack of space. Pulling an inboard-outboard engine is not really that hard of a job. You've just got to have the tool to align the outdrive with the motor. It also takes a tall hoist to get the engine over the side of the boat.

    If you had a closed cooling system, like a car, you could be looking for bubbles in the coolant. I don't know how you'd diagnose a 5.0 marine engine that'd froze.

  10. #10
    Captain erikgreen's Avatar
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    Default Re: Freeze plug replacement

    The right thing to do is replace them with standard brass plugs.. a set of these is only about $25. Put a little bit of RTV silicone gasket sealant on the edges before you tap them into place with a dowel (I use permatex).

    More importantly, pressure test your engine water passages before you go out on the water. If you popped the plugs, odds are good you also have an engine crack somewhere, and finding and fixing that could save you a couple thousand dollars over ignoring it.

    Having the engine run well means very little. I had a 305 (MC 228) engine that ran when it was half full of water. It only would have cut out when enough water got into the oil to completely flood the engine.

    Even if you don't see signs of water, pressure test the cooling system and do a leakdown test on the cylinders to see if there's a problem, otherwise you may end up out on the lake with no engine and damage to your boat you could have avoided.

    If the engine is going to break, it's going to do so on the water after being run at high speed under a load and in high stress conditions... it may look and work well on land then blow up on the water.

    Erik
    Sea Ray SRV-210 - Winter refit
    75-85 foot displacement hull trawler - gleam in my eye

  11. #11
    Supreme Mariner bruceb58's Avatar
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    Default Re: Freeze plug replacement

    Quote Originally Posted by Bamaman1 View Post
    Mercury and other boat manufacturers only rent out the GM engine factory something like one per year to cast engines to their specifications. The metallurgy and motor mounts are different on marine engines.
    Totally not true. Matallurgy and motor mount locations are identical.
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