water in oil

skipper_stu said:
"
never ceases to amaze me when peeps say that water comes back from the exhaust and enters sump! If it comes back up exhaaust then it gets past the ex valve and enters the cylinder. To get in to the sump it has to get past the piston rings. If it was that easy for water to go past the rings then there would be no compression. My guess, either oil inter cooler, rusted through engine parts (unlikely) or most likely if the raw water pump is integral, a worn back water seal.
S
Click to expand...

It most definitely does happen. When Owen worked for Sunsail they took delivery of a large fleet of new, identical boats. Before very long they began to experience seized engines and large amounts of seawater in sumps. Turned out that the trap was too small for the exhaust system with the result that water entered the engine. In the end they replaced 50(!) engines and traps.
 
superheat6k said:
I would question whether your statement here that seawater pressure is less than freshwater pressure is correct. When my heat exchanger (VP TAMD60C) developed a minute pin hole puncture the fresh water system filled from the seawater, not the other way around, manifest by coolant gathering in the bilge through the pressure cap. Even at 95oC the increased pressure in the freshwater system will be less than 1 bar, but the positive displacement seawater pump will easily achieve 2 bar.
Click to expand...

But the seawater system is (designed to be) open ended. As I said in the post, unless the manifold is clogged up the seawater pressure will always be less. I note that you have a Volvo, in which this problem is quite common. I did find that when the seawater injector into my Bukh engine became clogged, the resulting higher pressure between it and the pump resulted in very rapid wear of the pump seal. It is not designed to deliver much pressure, although being a positive displacement type it will do so.
 
VicS said:
Dunno... never heard of valve overlap until I read in in the OP's post. Perhaps skipper stu will explain it to us. He knows all things about all engines.

Yes the Op mentions an oil test but he does not say how much water, only that it showed up in the oil test



As You say it could be so slight as to be nothing to worry about. On the other hand it could be enough to cause concern.

The OP has been on line a couple of times this evening according to his profile and he has visited this thread. Why, one wonders, is he not offering any more information or clarifying any of the points raised.

It would have been nice to have known what engine is involved and also some indication of the level of seawater contamination.
Click to expand...
Valve overlap, commonly used on racing engines of my era. Where both valves are open together, it allows the charge of fresh mixture to have a built in velocity to give better volumetric efficiency. If the exhaust valve stays open a little longer, the effect of the megaphone can be tuned to help "suck" the fresh charge in. Which brings us neatly to the Mercruiser issue mentioned. If the exhaust system is accidently "tuned" by reason of exhaust system length/volume then a "flutter" could be set up in the exhaust system letting water in the exhaust flow the wrong way and back in to the cylinders.
S
 
skipper_stu said:
Valve overlap, commonly used on racing engines of my era. Where both valves are open together, it allows the charge of fresh mixture to have a built in velocity to give better volumetric efficiency. If the exhaust valve stays open a little longer, the effect of the megaphone can be tuned to help "suck" the fresh charge in. Which brings us neatly to the Mercruiser issue mentioned. If the exhaust system is accidently "tuned" by reason of exhaust system length/volume then a "flutter" could be set up in the exhaust system letting water in the exhaust flow the wrong way and back in to the cylinders.
S
Click to expand...

Thanks . That's obviously what the OPs engineer thinks may be the problem.

Various other suggestions made may or may not be valid. We don't really know until we hear from the OP again to tell us more esp exactly what engine.

I reckon he must be the victim of a chronic case of new user syndrome. I hope it wont prove to be terminal but he wont be the first to have given up all hope of recovery from this.
 
A common problem with planing power boats is water getting into the exhaust when they stop quickly with engine at idle and the stern wave catching the boat and going up the exhaust
 
Sorry for not getting back to you all! I have twin 6.2 mercruiser inboards, the compression test was fine, they replaced all 4 exhaust assemblies, manifolds, risers, elbows and exhaust hoses to the fiberglass cross over's. put in the resonators, changed the oil and took the boat out for a 2hr. run, a new oil sample was taken and it was fine. the old Na number was 634,(don't know how much salt that is). the new number was 20, I'm assuming there would be some salt still inside from the oil that was left over from the oil change?
 
Sound encouraging, maybe 634 units, (ppm??) of sodium is highish, I don't know, but an isolated oil test doesn't give much firm information, rather a baseline.
A trend showing up from later tests would be more useful.
Sodium can arise from detergent additive to oil, so results could pehaps vary a lot between different brands.
Hope the cost of the work proves to be justified!
 
RichardS said:
1613 what? Grams of sodium chloride per kg / litre of oil?

Richard
Click to expand...

same units that the OP used in reporting the sodium to be 634. µg/ml perhaps

unless of course he was using millimoles / ???. Then it would be 634.
 
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