1992 Mariah overheat then got water in cylinders

Yesterday my overheat alarm went off on our way back home. I stopped and shut the boat off of course, but when I did there was a gurgling sucking sound for a bit I never heard before. During the teardown of my raw water pump only to see that the impeller was fine I pulled the thermostat to see that the it looked like an archaeological discovery. I assume it stuck closed and caused my issue, but I will verify today with a pot of boiling water. Could be an air sucking issue too, and I will rectify that as well. However, the starter would move the engine but wouldn't turn it over. I knew better than to keep trying and pulled the spark plugs before turning it over again. It blew water out of at least 4 holes which confirmed my suspicion. My question is how did that happen!? What failed in method or system that caused my boat to suck water up the exhaust into the cylinders? How do I prevent this from ever happening again? 351 PCM carb'd engine btw.

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Well it starts after getting all the water out of the cylinders. Quite a bit ended up in the oil. About to head to the river and see if the raw water pump sucks and keeps her cool without a thermostat. Hopefully skidim can get me the right one before next weekend.https://uploads.tapatalk-cdn.com/201...cc73c81995.jpg

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I am confident the water came from a blown head gasket due to overheating if you are lucky.

Worse case is a cracked cylinder and or head.


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Well that sucks.

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I guess a compression check is in order rather than a river test.

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When you overheat on the water and shut down the engine it will create a vacuum in the exhaust and suck the water into the exhaust manifolds and through the open exhaust valves into the cylinders. First find out what caused the overheat . The head gaskets may not be bad.

Quote:

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Originally Posted by michael hunter

When you overheat on the water and shut down the engine it will create a vacuum in the exhaust and suck the water into the exhaust manifolds and through the open exhaust valves into the cylinders. First find out what caused the overheat . The head gaskets may not be bad.

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Michael I'm fairly sure a stuck thermostat and possibly an air leak in the raw water line caused the overheat. We didn't overheat on our way out for the day, but on our way back. All we did was ride out to a spot, anchor, and then ride back a few hours later. Thermostat pic attached for reference. I pulled and twisted on the crunchy grungy thermostat before putting it in a pot of hot water, because I'm fidgety I guess and couldn't leave well enough alone. The thermostat operated correctly (began opening about 145*) in the pot, but who is to say it would have before i messed with it. The impeller and raw water pump are in good shape.The hose ends on the raw water pump inlet and trans cooler inlet were in rough shape so I cut them off clean and got a much better seal. I didn't realize how bad they were. I will do a compression check tonight after work with fingers crossed.https://uploads.tapatalk-cdn.com/201...d476c747b8.jpghttps://uploads.tapatalk-cdn.com/201...a1f54177ec.jpg

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Compression test results engine cold and plugs out.

1) 135
2) 145
3) 145
4) 145
5) 135
6) 140
7) 130
8) 140

10.4% variation, but nothing seems wrong to me. Thoughts? I would think a blown head gasket would show up as a dead duck.

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Blown head gasket won’t always show with a compression test. On a car you would do a cooling system pressure test, but would be tricky on an open loop system.


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Buy some cheap oil and oil filters change oil and filter run for a few minutes and change it again. It may take 3-4 times to flush the oil out . Then put your normal oil and filter and give it a try. Keep an eye on the oil and make sure its not water contaminated. If you get water again pull the heads.

I had a friend that was in same situation. Once he flushed the oil out of the system, he ended up fine. Replaced most of the older parts that were there for years/years, hoses, pump, impell, etc. Claims the early shut-down and tow-in helped too. Good luck.

Thank you guys for the advice. I will run it tonight on the hose and see if we can get all the water out of the crankcase. Goal is to head to the lake afterwards this week to see if the raw water pump will suck. Parts from SKIDIM should be here tomorrow.

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New thermostat is in and opens at about 140 to 150 and temp stays steady on the hose. The oil that was in it got changed and the fresh oil is getting drained tonight for another fill to hopefully get the rest of this water out. I only ran it long enough to get it up to temperature and observe that it didn't climb any higher for a period of time . This oil change looks better than the last so hopefully the bull is on the run. When I took the thermostat housing off to clean up the gasket surfaces I found an old piece of an impeller. The one that's in it now looks good so I know it didn't come from that one but somewhere in this boat's previous life it must have eaten one and the owner did not find all the pieces. https://uploads.tapatalk-cdn.com/201...fc2a923f69.jpghttps://uploads.tapatalk-cdn.com/201...c0cd731960.jpg

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This evening after another oil change I was running it on the hose to get this batch hot and verify I was still ok. I noticed a hot smell, and my wife said there wasn't any water coming out of the exhaust, while checking over the area for leaks and saw the temp gauge at 160. Now I know this is a 143* thermostat and there is no way we should be that hot at idle with good cold water. So off comes the raw water pump discharge hose and I fire it back up. Guess what comes out. NOTHING! Not a drop of water. So, off comes the water pump again for inspection. This time you could clearly see that the hub had separated from the rubber. *sigh* Out with the old and in with the spare I just got and we are now discharging LOTS of water from the exhaust and she is cool all over. Ran for half an hour, probably, just waiting for the next thing to bite me in the hind end, but no problems. This oil dump had no apparent water so I'd say I'm safe there. Headed to the lake tomorrow morning. Wish me luck.https://uploads.tapatalk-cdn.com/201...1d785635c1.jpg

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No issues today with the raw water pump, plumbing, thermostat, or oil. Boat ran good and stayed cool. I believe I will add a water pressure gauge, since I would have known as soon as we got in the water last weekend that the impeller wasn't doing its job. Thanks for all the help.

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Obviously a case of , when you buy a used boat always start with a fresh impeller. Glad your motor is ok.

Some say it is overkill to replace it every year, so I thought I would just inspect and reinstall too. It certainly doesn't protect you from what you can't see between the hub and the rubber. So, I'm in the new impeller each year and the old one as a spare in the toolbox club now.

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