Hydro-locked engine

[ahein]

First the particulars... 1987 GM Marine 350ci coupled to an AQ-275 Volvo outdrive. The original engine was replaced a couple of years ago with a new GM 350ci. At that time a closed cooling system was added to increase engine life. This was what was known as a "half-system" where the engine is freshwater cooled but the exhaust manifolds were raw-water cooled via the crank mounted seawater pump.<br /><br />Now the problem... De-winterized the engine a few weeks ago and started it up with no problems. Ran great in the yard on muffs. Took it down to the bay last week and took the boat for a sea trial. Ran great but noticed a little "surging" at idle rpms. Took it home and ran it again on the muffs for almost a hour to flush the exhaust and make some minor adjustments. Took it back down to the bay a few days later to test a new prop but engine would not start. It would barely crank over so my initial thought was dead batteries. <br /><br />Took the boat home and after testing the batteries, found that they were ok. Further investigation revealed that the engine was hydro-locked. Removed the plugs, cranked the engine, and water shot out of cylinders 3,4,5, and 6. These are the middle two cylinders on each bank. The water was clear and not green, so I know its not mixed with antifreeze. There does not appear to be any water in the oil. Antifreeze level in the closed cooling system seems to be normal and there is no volume increase in the oil pan.<br /><br />With these symptoms, I believe I can eliminate water ingestion through the intake manifold, heads, or block water-jacket. Agree? It also appears that the most likely culprit is the exhaust manifolds. I removed the exhaust manifolds and found some rust between the heads and the manifold gaskets (on both banks). This appears to be the source of the water ingestion.<br /><br />So my questions are... Would you agree or disagree with my diagnosis? Would you check any place else for for water ingestion? Is there any way to test the exhaust manifolds for leaks that would allow water to go back into the exhaust ports? <br /><br />Sorry for the really long post. I was thinking and diagnosing while I was typing. All comments are truly appreciated.<br />Thanks,<br />Andy

 

[Don S]

Re: Hydro-locked engine

There are no water passages between the manifolds and the head, so that wouldn't be the problem. But you do have water between the manifold and risers. Remove the risers and check the surfaces of both the riser and the manifold for clean shiny metal. Black carbon based surface is a sure sign of problems.<br />Here is a picture of a Merc manifold, but the principal is the same.<br /><br />

 

[ahein]

Re: Hydro-locked engine

Thanks Don. I'll split the manifolds and risers and check (replace) the gaskets. So any carbon in the areas indicated would mean that exhaust gases are leaking past the gaskets and into the water jacket, right? It would follow that if exhaust can leak past then water could also.<br /><br />Do you know of any way I could pressure test the manifolds/risers before I bolt them back up?

 

[KaGee]

Re: Hydro-locked engine

This is applicable and useful for all brands as well.

 

[ahein]

Re: Hydro-locked engine

Thanks KaGee. I am most concerned about the section that talked about internal cracks in the exhaust manifold or riser. The manifolds are only two years old, thoroughly flushed after every use, and completely drained of water during the winterizing process but I don't know for sure if there might be cracks allowing water to leak by. I will replace the riser and manifold gaskets, but I'd like to be able to test the exhaust assemblies before I put them back on. If I could pressure test them somehow I believe that would tell me if I had any internal cracks. Thoughts anyone?

 

[ahein]

Re: Hydro-locked engine

OK, I checked compression in each cylinder and got the following results.<br /><br />#1 - 153 psi #2 - 150 psi<br />#3 - 165 psi #4 - 150 psi<br />#5 - 160 psi #6 - 150 psi<br />#7 - 165 psi #8 - 150 psi<br /><br />The compressions on the starboard bank are all the same and the compressions on the port bank are all within 10% of each other, so I'm pretty sure I didn't do any internal damage to the engine after hydrolocking. Going to change the oil and filter as well.<br /><br />Does anybody have any suggestions or precautions I should take before I bolt everything back up and try to start it? Anything I should be wary of after I let it run for awhile?<br /><br />Thanks, all comments are appreciated.<br />Andy

 

[rodbolt]

Re: Hydro-locked engine

yep, while ya got it apart check the manifolds and risers very carefully. you can make a block off plate with wood and use a garden hose on the seawater inlet to the manifold and test the manifold for leaks.<br />as it hydrolocked there is only two ways to get water into the cylinders with closed cooling. one is it happened when ya backed it down the ramp and the other is manifold or riser is busted.<br />unless your neighbor is mad and poured water down the carb.

 

[ahein]

Re: Hydro-locked engine

Well, I split the risers and manifolds and, lo and behold, I found rust trails between the gaskets and the fore and aft lands of the manifold. I believe this is the source of the water ingestion, but I'm gonna hydrostatically test both manifolds as Rodbolt suggested before I put them back on.<br /><br />Thanks to all who responded. I'm really impressed that my problem attracted the attention of some of the "big guns" on this board (Two Admirals and a Supreme Mariner, no less ). If anyone else has any suggestions before I restart my engine, I'm all ears.<br />Thanks again,<br />Andy

 

[rodbolt]

Re: Hydro-locked engine

I aint a big gun, I just happen to fix them for a living for a year or two.

 

[ahein]

Re: Hydro-locked engine

Well, I think life is good again. . I bolted everything back up, changed the oil and filter, reconnected the batteries, and fired it up. Ran it at idle for over a half hour. Water temp normal, oil pressure normal, charging normal. Ran a touch ratty at first (sounded like surging at idle), but straightened out after about ten minutes. I shut it down and removed all of the plugs, then cranked it over a few times. No water from any cylinders! I did a proper compression check (engine warm, throttle wide open), and came up with the following:<br /><br />#1 -165 #2 -165<br />#3 -160 #4 -165<br />#5 -170 #6 -165<br />#7 -165 #8 -160<br /><br />Started it up again and it ran great! I'll take it out in a few days and check everything under load. Keep your fingers crossed.<br />BTW- My comment about the "big guns" was a compliment to those who responded. I truly respect your opinions and advice, and always read what you have to say about other people's problems. Keep up the good work.

 

[KaGee]

Re: Hydro-locked engine

A good 20-30 minute hard run should take care of eliminating any residule condensation if your leak is fixed.

 

[Bt Doctur]

Re: Hydro-locked engine

missed one, rodbolt. customer had his daughter helping wash the boat. unknown to him , his daughter washed out the "thru hull exaust tips" with soapy water and a hose.boat wouldnt start next week.