Hot at Low RPM, Now water in Cylinders 3 and 6.

[Chickenbone]

Hey guys. Need a hand here. First boat, still learning. Bought an '88 OMC 4.3L V6 on 17ft Sunbird. Guy I bought it from had an overheat that melted the left breather hose to the flame arrestor. Apparently the manifold got really hot. Anyway, I changed the impeller, flushed all the water passageways and put it on muffs. Engine ran fine for 30 minutes, no problems.
Put it on the lake and it overheated at idle and low rpms. On a plane the temp quickly came down to normal. So we basically just cruised around for about a hour and enjoyed the ride. We decided to stop and turn off the engine for a few. I noticed a water-running sound from the engine. Tried to start it back, and it seemed to be seized. Had to be towed.

Back home, pulled plugs and got water from 3 and 6. (closest to stern?) I have not checked the flappers, but optimisticly hoping that they have melted and allowed some water into the cylinders. I got all the water out, and have spayed penetrene into the cylinders. Have not tried to start the engine with the starter, and not sure of the best tools to spin the harmonic balancer by hand. Don't want to break a bolt by using a wrench. Is there a standard procedure for troubleshooting this? And do the exhaust Manifolds have to removed to get to the flappers?

I know this is a common issue, but since it occurred right after an overheat (still diagnosing that problem too) I'm hopeful I could still not have to break out another thousand. Thanks!

 

[Bondo]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

Hey guys. Need a hand here. First boat, still learning. Bought an '88 OMC 4.3L V6 on 17ft Sunbird. Guy I bought it from had an overheat that melted the left breather hose to the flame arrestor. Apparently the manifold got really hot. Anyway, I changed the impeller, flushed all the water passageways and put it on muffs. Engine ran fine for 30 minutes, no problems.
Put it on the lake and it overheated at idle and low rpms. On a plane the temp quickly came down to normal. So we basically just cruised around for about a hour and enjoyed the ride. We decided to stop and turn off the engine for a few. I noticed a water-running sound from the engine. Tried to start it back, and it seemed to be seized. Had to be towed.

Back home, pulled plugs and got water from 3 and 6. (closest to stern?) I have not checked the flappers, but optimisticly hoping that they have melted and allowed some water into the cylinders. I got all the water out, and have spayed penetrene into the cylinders. Have not tried to start the engine with the starter, and not sure of the best tools to spin the harmonic balancer by hand. Don't want to break a bolt by using a wrench. Is there a standard procedure for troubleshooting this? And do the exhaust Manifolds have to removed to get to the flappers?

I know this is a common issue, but since it occurred right after an overheat (still diagnosing that problem too) I'm hopeful I could still not have to break out another thousand. Thanks!

Ayuh,.... Welcome Aboard,... Which exhaust manifolds do you have,..??

If they are the 1 piece units, I'd suspect They are yer water leak,....

 

[Chickenbone]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.



http://www.**********/parts/search/OMC/SternDrive/1988/432APRGDP/EXHAUST & COOLING/parts.html

 

[Bondo]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

View attachment 210477
View attachment 210478
http://www.**********/parts/search/OMC/SternDrive/1988/432APRGDP/EXHAUST & COOLING/parts.html

Ayuh,.... There's yer Problem, Right there,.....

Find the 2 piece manifold, 'n riser conversion,....

Because of core-shiftin' in the castin' process, those things have been Killin' motors since the day they came out,....

Thank God, they aren't even made anymore,...

 

[Chickenbone]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

Thanks! I feel slightly more hopeful, but if its a manifold issue, isnt it kinda coincidental that they both leaked water into cylinders at the same time?
I'll look into the two piece!

 

[Howard Sterndrive]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

isnt it kinda coincidental that they both leaked water into cylinders at the same time?

running dry with no cooling water through them could be what finally busted the rusty/weak castings up inside.

As far as rolling the engine by hand, I find a wrench on the alternator pulley nut along with pressure/push on the vee belts will roll it. Just watch the fingers.

 

[Chickenbone]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

Thanks Howard. Here's an update: I pumped all of the water out of the cylinders and it was very brown and rusty. I also sprayed PB Blaster into each cylinder. I cannot turn the engine by hand. Tried the alternator pulley, but it just turns while belt slips. The Harmonic Balancer will not turn. I hoping that a little soaking/re-applying the lubricant will help free things up, but so far it looks bad.

Question: The water in cylinders had been there for around 1 week. But it seems to me that amount of rust came from the manifolds, rather than from the pistons/cylinder walls actually rusting. Did I wait too long? My next step is to take the whole boat to my local marine mechanic, but its gonna be a couple of weeks before i can afford any major work. I want to at least prevent future rusting and try to salvage what is still good. Meanwhile, is there anything else I should do? Should I try to spin it with the starter. Dont wanna break anything (else).

 

[TheHunter990]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

A week with water sitting in cylinders is WAY to long. You have rusted the pistons to the cylinder walls. Also water will have seeped down into the engine oil.

At this point, if it were mine, I would replace engine oil, and see if the starter will break it lose, alternative is a complete teardown of engine and rebuild.

 

[Chickenbone]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

Thanks. I was afraid of that. I had checked the engine oil. The level and consistency looked OK on the dipstick, but I did see a tad of milkshake in the oil cap. This tells me that only a small amount (still too much I know) of water got into the engine oil. It's worth $25 and an hour of work to change it. Will try that and post update over the weekend. Should I use any type of additive in the oil?

 

[Lou C]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

I have had 3 sets of those manifolds on my 88 (salt you change at 5 years to be safe) and have never had water in the engine. If you had an overheat the flappers are likely melted and could have dropped down and blocked the exhaust. I recently had an overheat because the hose from the transom to the ps cooler popped off. Engine hit 240, after I stopped I checked the manis with the IR temp gun and they were at 375*F. Took the boat home, took off exhaust. Flappers toast, ex hose OK but replaced any way cause they were OE. Filled manis with acetone no leaks. Checked compression same as 3 years ago. No water in oil. Ran on the bay 2x and it was fine, normal temp no water in oil. Not sure what caused your problem but I wonder if it's previous freeze damage.

 

[Chickenbone]

Re: Hot at Low RPM, Now water in Cylinders 3 and 6.

I bought this boat for $1500 from a friend, who had overheating problems and just didn't have the time or patience to investigate. When I got the boat, the righthand manifold had apparently gotten so hot that it melted the breather hose going to the flame arrester. Also, the boat had almost no oil in the engine. I later discovered that the oil pan plug was leaking. I replaced the plug washer and changed the oil. Replaced the impeller kit and did a muff test. It ran great in my driveway for at least 30 minutes. So we went on the lake, where it would get pretty hot at low rpms and idle. On a plane, the temp quickly went down. We kept the boat moving as much as possible and enjoyed several hours at normal temps. Afterwards, we stopped the engine to stop and enjoy the sunset and a beverage for a half hour or so. During this time, we noticed the sound of water running (dripping) inside the engine compartment somewhere. (Not sure what this was). Upon trying to restart, the starter would not turn the engine over. We had to be towed. A few days later, I removed the plugs to find the water in the cylinders. I got this water out and sprayed tons of PB Blaster in each cylinder. Still cannot turn over by hand.

The water running sound we heard could have been water running from the manifolds into the cylinders. I'm hopeful that since the engine was running fine when we turned it off, that the head or block is not cracked, and that maybe my manifolds simply gave way.

An even more hopeful scenario, is that maybe as we stopped, the flappers had melted and water ran into the engine that way. My girlfriend was driving, and she did stop pretty suddenly. Ive heard mixed reviews on the likelihood of water backflowing through the exhaust. Some have even said the flappers are unnecessary. ???
Havent had time for a pressure test yet, but I'm gonna keep trying to turn the engine over a few more times. Thanks for sharing your experiences.