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Overheating Problem

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  • Overheating Problem

    1988 Seaswirl Spyder 202 w/OMC Cobra 5.7l (a.k.a Small Block Chevy). Previous lake trip my impeller got ate up at some point and the boat got hot, maybe 240 ish? Unfortunately I was not driving at that moment. I smelled it and killed it. We stopped and I let it cool down. Wouldn't turn so I pulled the plugs and discovered water in cyl. 4,6 and 8. A pretty good amount too. Pulled the boat out, stopped at the first auto parts store and fogged the cylinders to prevent it from rusting. Got home and did a compression test. I was at 150ish on all 8 cylinders. Pulled the risers and exhaust manifold. The exhaust flappers were melted so I replaced them, new gaskets and reassembled. Assuming that the amount of water in there was a result of bad flappers. Hit the lake yesterday, boat ran hotter than usual but was stable at 220ish (normal is 175 or below). However, it would cool back down when idling or running near 1500rpm. It stayed steady at that all day. And ran great. Blamed it on bad gauge. Finally on the way back it started climbing a bit so I slowed down, immediately heard lifter tapping and smelled burning oil. Shut it off and it kept running (dieseling), I threw it into gear and bogged it out. There was a rubber smoke (belts maybe?) Coming out of the engine bay. I could smell burnt oil and it was dripping from the PCV's as well as steam. I then heard a whoosh like water going into the cylinders twice for about 2 seconds. Not sure which side. Checked the dipstick and no oil (was full at lunch). Pulled it out and pulled the plugs about an hour later with no water signs present. Checked oil again and It was a QT low (no water present). It would start, but would shut off seconds later. Compression was low in 3. (115), 7.(120),8. (130). The rest were 150ish. Attempted a start today and it sounded like absolute garbage. The belts squealed when you gave it throttle. So I killed it. I figure I'm looking at head gaskets, getting heads checked, impeller and maybe a water pump. Any other thoughts?

  • #2
    When you saw it running at 220 which is way hotter than normal, that was a warning sign. What might have happened is that the previous overheat may have melted one of the water tube gaskets in the outdrive, this would prevent the impeller from sucking in enough water to keep the engine cool, while the boat was up on plane. Whenever you have a bad overheat, there is a risk of melting one of those or both, just like the flappers because you have hot exhaust going through that part of the outdrive with no water to cool it off. If you blew both head gaskets, its a bit of a job but not that bad. Hopefully you did not also crack the heads. I had a bad overheat back in 7/2013 and it ran fine for 2 more seasons (had melted flappers, melted water tube gasket) and then at end of last season, I had water in a cyl, both head gaskets had blown. I took it apart and the heads had cracks in the center cyl exhaust valve seats. Working with a machine shop the best option was to install a set of remanufactured marine heads. That and a new exhaust system (salt water use, have to change it every 5/7 years) and its up and running again. When you take it apart make sure to check the block for warpage (less than .003") and the sealing surfaces of the intake manifold (same, less than .003"). Make sure to use marine gaskets. Keeping it all clean and making sure the head bolt threads are clean are very important. I replaced my head and manifold bolts with APR bolts due to the originals being pretty corroded.
    1988 Four Winns 200 Horizon
    4.3 OMC Cobra

    98 Jeep Grand Cherokee 4.0 Selectrac
    07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

    "While air doesn't freeze....rust never sleeps"


    • #3
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