Water in cylinders after overheat, what to check next?

[jeeper31]

So this is depressing. I just rebuilt the 350 chevy small block engine and took it out on it's maiden voyage this weekend. Everything was going perfect until we headed back to the marina, as we were cruising I looked down and saw the temp gauge was reading 240F, I brought the engine down to idle and shut it down. We pulled the engine compartment door open and there was a fair amount of white smoke coming from the engine. I let it cool for a while and then went to start it, all i heard was a hard click from the starter like it wanted to turn the engine but couldn't After that we were towed in.

Part two, went out to the boat the day after and pulled the plugs on the engine. I then cranked the engine by hand and a ton of water came out of cylinders 1,3,2,4. So next I checked the oil and it was pretty high over the full mark, like there was water in it. Next I did a compression test on all 8 cylinders and they all came back at or a little below 120 PSI.

So my question is this, where could that water have come from? I was thinking blown head gasket when i first saw the water but now I'm not sure since the compression test came back just fine. I am wondering if I blew out my exhaust riser gasket and the water backed into the engine that way. Thanks in advance for any help!!!!

 

[ktbarrentine]

Re: Water in cylinders after overheat, what to check next?

A simple theory is that you had an overheat caused by a failure of your O/D water pump (either the impeller is shot, or you sucked a plastic bag or other object over the intakes). This high (240) degree of overheat melted your shutters and subsequently allowed water back in to the engine after you shutdown/backed down off the throttle). You can do an engine recovery process (sounds like your compressions are good. Get that water out now! (to avoid rusting, etc).
And....you need to address the overheat issue (recommend pull the drive, inspect the impeller). Also recommend pull your elbows and inspect the shutters. Those are easy checks, even if you find no issues there, need to look.
What drive do you have (S/N would be good). If pre-gen II, then need to take a good look at your water pocket cover, too. That amount of overheat would typically melt a waterpocket cover in your drive. keep us posted. best of luck!
(theory based on symptoms given)

 

[jeeper31]

Re: Water in cylinders after overheat, what to check next?

Thanks for the reply! The engine serial number is B520471, it's an MCM 260. So this boat I have is a bit of a Frankenstein of a few other boats. The exhaust system is off an OMC (I think Alpha, must have been the previous engine in the boat) so I'll check the shutters on that guy and see what kind of shape they are in, my guys is they are baked. Your theory of water backing up into the engine through the exhaust does make sense. While we were waiting 40 minutes for a tow several huge boats came by and threw some very large wakes our way rocking the boat big time, that could have been another opportunity for water to enter the exhaust.

One more question, what exactly do you mean by engine recovery process? I was going to replace the oil and spark plugs and then see if she'll start. Are there some other things I should check before starting? Thanks again for the help!

 

[Chris_94_Sprint_TX]

Re: Water in cylinders after overheat, what to check next?

Sounds like KT pretty much nailed it. Another possible cause is the water jackets inside the block could have been cracked during the over heating or even prior too that event. I have had this happen on a few cars and every one of them still had good compression numbers (a Little low but good).

Chris

 

[LiquidC]

Re: Water in cylinders after overheat, what to check next?

Something similar happened to me a few months ago, it was mainly due to a high water line. I replaced a 4.3 V6 with a 5.7 V8, and the extra weight of the motor brought the water line up slightly & allowed water up the Y-Pipe when I had her loaded up with passengers. The solution was to install riser extensions.

You may want to check your waterline with this new motor. What was in there before? Same thing?

I'd check your impeller first & replace it either way, they're pretty cheap.

Other than that, check your riser gasket, and maybe the intake manifold gasket. Problems with head gaskets are rare on boats. You may have melted your water shutters, like ktbarrentine said, so you'll want to pop off your elbows & check 'em out. Fish out any missing chunks.

I'd get the water out ASAP. Remove all plugs & turn her over for a bit. Squirt some motor oil in each cylinder & install new plugs. Change the oil & filter, and then run her on the muffs. When she gets up to temp (160 - 180) take a look at the exhaust smoke & see what it looks like. If it's white then you're getting water into the cylinders & exhausting water vapor. Hopefully it was just the impeller.

Good luck

 

[ktbarrentine]

Re: Water in cylinders after overheat, what to check next?

One more question, what exactly do you mean by engine recovery process? I was going to replace the oil and spark plugs and then see if she'll start. Are there some other things I should check before starting? Thanks again for the help!

Might take a couple of oil changes depending on amount of water taken in (and what your drained oil looks like). Just need to make sure you address the water in the cylinders fairly quickly to avoid surface rusting (happens fast in the cylinders). Need to make sure you have a "good" water supply to engine if you do this with the drive off (garden hose secured to the water inlet port on the bell housing). Should be ok to check with the drive on using muffs, but with a suspect impeller and suspect bad shutters, need to be careful of hydrolocking again (no throttle chops, keep RPMs about 1300, use a guy to help turn water on just before start and off immediately after engine off, avoid excessive flow/pressure from garden hose, etc.). Best of luck!

 

[jeeper31]

Re: Water in cylinders after overheat, what to check next?

Right now the boat is sitting in a wet slip at the marina so I'll be doing my inspections/repairs while it's in the water. It's a big boat (27ft) and a real pain to get on the trailer. Lucky for me the exhaust tube comes up pretty high over the water line so I shouldn't flood the boat when I pop the risers off. As for the impeller it sits at the top of the outdrive and I'm pretty sure I can get at that while the boat is in the water as well. I'll post back what I find out later on. If you guys think working on it in the water is a bad idea let me know, I'm still pretty new to all this marine mechanic stuff, I'm used to jeeps

 

[ktbarrentine]

Re: Water in cylinders after overheat, what to check next?

IMO, these types of engine disassembly/checks on the water are risky. What drive do you have? You cant do any outdrive maintenance in the water (other than to replace propeller).

 

[Volphin]

Re: Water in cylinders after overheat, what to check next?

Those exhaust tubes are solid as a rock now. You will need to replace them as well as the shutters.

 

[jeeper31]

Re: Water in cylinders after overheat, what to check next?

I have an OMC cobra outdrive. I can get to the impeller while laying on the swim deck, I think. When I check the exhaust I'll be sure to re-assemble everything before I leave. I've read of boats that have sunk because a mechanic left the exhaust apart while the boat was in the water and then water entered the boat while no one was around.

 

[ktbarrentine]

Re: Water in cylinders after overheat, what to check next?

Ok...good to know (OMC drive)...I assumed (shame on me) that because you are in the mercruiser I/O forum that this was a mercruiser outdrive. Hopefully someone with OMC outdrive experience can chime in.

Meantime, check out this similar thread in the OMC forum just for S&Gs. I learned abit more just in the few minutes thumbing through it.

http://forums.iboats.com/omc-i-o-in...-cobra-454-overheating-loss-power-486364.html

Also....just like in this (mercruiser) forum, there is a ton of good OMC outdrive info in the "stickies" at the top of the OMC I/O forum.

 

[jeeper31]

Re: Water in cylinders after overheat, what to check next?

No worries. I have kind of a strange set up, I have parts from all kinds of different boats. Anyhow, I found this thread on changing the OMC impeller while the boat is in the water, seems like it shouldn't be too bad.

changing a omc cobra impeller

 

[LiquidC]

Re: Water in cylinders after overheat, what to check next?

Make sure you use a floating ratchet :laugh:

 

[jeeper31]

Re: Water in cylinders after overheat, what to check next?

Well KT you hit the nail directly on the head. The exhaust shutters are scorched and are now hanging by a thread in the exhaust tube and will have to be replaced. The only down side is they are too far down the tube to be changed in the water, I'll have to get the boat pulled. I haven't checked out the impeller yet, I'll just wait until the boat is out of the water to change that (much easier). I'll post back when I get to the bottom of the overheat problem. Thanks again everyone for all the advice!