Seized Engine then Runs Fine

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dkpero

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On a Merc 175 Offshore, cruising at a little over 5000 rpm for about a minute, upon lowering the throttle, the engine sputtered and died. The engine was seized. 20 minutes later the engine started, running a little rougher than normal, a little louder. Have taken the boat out for another 3 hours with no problems, other than rougher idle and low end and maybe a little more smoke. Runs beautiful at 3000 rpm plus. Any ideas as to what could be wrong??
 
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Fouled Plug

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Re: Seized Engine then Runs Fine

If you're still pumping enough water, your "seizure" could have been from lack of lubrication. Have you tested the compression on all of the cylinders since the incident?
 
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dkpero

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Re: Seized Engine then Runs Fine

Fouled Plug, Thanks for the information. I plan to do the compression test within the next couple of days. Any advice on the test, other than looking for all 6 cylinders to be close?
 
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dkpero

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Re: Seized Engine then Runs Fine

Hey Fouled Plug or anyone else,<br />What do you think about the possibility of water entering into the engine through the top exhaust port? Are the symptoms indicative of this? Thanks. :)
 
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Fouled Plug

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Re: Seized Engine then Runs Fine

Have you had a chance to pull the plugs and check 'em out? Their condition can tell you a lot. As for the compression test, nothing special there. It won't give you the best readings cold, but it will give you an idea of what you've got. Post the #'s when you get them.
 
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dkpero

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Re: Seized Engine then Runs Fine

Fouled Plug,<br />When I removed and cleaned the plugs prior to the last time out, they were clean with a sligh oily misting on them (same as last time I took them out). I'll post the compression numbers in a few days. What do you think about the "swamping" possibility that I mentioned earlier?
 
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Fouled Plug

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Re: Seized Engine then Runs Fine

Anything is possible, but I would expect you would have seen one (or more) really clean plugs with water in the system. They tend to come out looking spotless,(steam cleaned) or with droplets of a milky goo on 'em.
 
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dkpero

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Re: Seized Engine then Runs Fine

The compression numbers are in, and they aint good.<br />Port: 1 125, 3 20, 5 122<br />Starboard: 2 125, 4 125, 6 128<br />I'll pull the port head cover to look for scoring this weekend.
 
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Fouled Plug

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Re: Seized Engine then Runs Fine

Ouch! Sorry to hear about your unfortunate #3 cylinder. Did the spark plug have any aluminum deposits on it? Hopefully you won't find anything too nasty when you peek inside. Good luck!
 
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dkpero

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Re: Seized Engine then Runs Fine

No deposits on the plug, just a little oily. Hopefully that means minimal damage. I noted that the #3 plug was much oilier than the other 5. What do you think about just honing the cylinder and replacing only the single rings and maybe piston and bearings on that rod?
 
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dkpero

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Re: Seized Engine then Runs Fine

Upon opening the head, a piston had fractured and damaged the cylinder lining. I honed the cylinder for several minutes to take out nearly all of the marks. A couple very slight (barely detectable with fingernail) longitudinal marks are still present, but I didn't want to take off any more material to remove them. The dimensions seem to be OK, so I'm installing a new piston, rings, rod bearing and seeing how she holds up.
 
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