Sea water back-flow through engine

[dperchlik]

If your engine is below the water line this can happen and did to me. Water would slowly flow through the engine, fill up the water lift muffler and when I would crank would get water in oil. I turn off the through hull when ever I shut off engine. No longer have the problem but it is an extra step to open the engine room and shut the valve.

[Corrosion-Eng]

Connecting battery negative to any metal that can get damp or wet creates stray current that generates marine electrolysis corrosion. The CAUSE can be corrected.
Use Google to search for marine electrolysis and click on Conquer marine corrosion CAUSE.

[Wotname]

The OP's friend has two problems (on both engines) -

a). low compression on #4 on both engines; presumably this has been confirmed by a compression tester.

b). water entry to the internal oil sections of both engines.

Both need fixing (I know - obvious). Assuming both problems are concurrent, it is reasonable to assume the cause is the same on both engines and also that (b) caused (a).

It is unreasonable to think that a similar component failure happened concurrently on both engines so this leads me to think it a design issue in the installation - again assuming both engines are similarly installed.

Water entry is more like to be from the exit end of the exhaust system but it is possible that it might be from the entry side of the raw water circuit.

It seems to me that the focus should be on how the water can enter the system from the exhaust outlet and once that is eliminated, look at the how the water might be forced though the raw water entry side - looking only at the particular design issues.

If both of these are eliminated, it is possible (but not probable) there has been a simultaneous component failure of each engine allowing water into the oil side. Maybe seals gone on the raw water pump (if shaft driven) etc.

Personally I wouldn't bother about worrying about the battery negative lead - I reckon more than 99% of recreational boats have this arrangement without issue - leave that for the conspiracy theorists - might be true somewhere but so unlikely... right up there with bad fairies pouring water into the engines when you aren't looking. I might wrong thou

[Karanga]

A) Perfect description of the situation
B) Excellent process to identify the cause (find the flaw in the design)

Compression testing was done about 1 month ago. Cylinders 1 to 3 were consistently 450 (psi?). Cylinder 4 on each motor was variable and as low as 150. Injectors were tested, and serviced. Glow plugs were all dead(!) and replaced.

Originally Posted by Wotname

The OP's friend has two problems (on both engines) -

a). low compression on #4 on both engines; presumably this has been confirmed by a compression tester.

b). water entry to the internal oil sections of both engines.

Both need fixing (I know - obvious). Assuming both problems are concurrent, it is reasonable to assume the cause is the same on both engines and also that (b) caused (a).

It is unreasonable to think that a similar component failure happened concurrently on both engines so this leads me to think it a design issue in the installation - again assuming both engines are similarly installed.

Water entry is more like to be from the exit end of the exhaust system but it is possible that it might be from the entry side of the raw water circuit.

It seems to me that the focus should be on how the water can enter the system from the exhaust outlet and once that is eliminated, look at the how the water might be forced though the raw water entry side - looking only at the particular design issues.

If both of these are eliminated, it is possible (but not probable) there has been a simultaneous component failure of each engine allowing water into the oil side. Maybe seals gone on the raw water pump (if shaft driven) etc.

Personally I wouldn't bother about worrying about the battery negative lead - I reckon more than 99% of recreational boats have this arrangement without issue - leave that for the conspiracy theorists - might be true somewhere but so unlikely... right up there with bad fairies pouring water into the engines when you aren't looking. I might wrong thou

[Wotname]

Originally Posted by Karanga

A) Perfect description of the situation
B) Excellent process to identify the cause (find the flaw in the design)

Compression testing was done about 1 month ago. Cylinders 1 to 3 were consistently 450 (psi?). Cylinder 4 on each motor was variable and as low as 150. Injectors were tested, and serviced. Glow plugs were all dead(!) and replaced.

Thanks

Leaving aside the potential design issue causing water entry for a moment, can we assume water is no longer getting into the engine?

The compression numbers would suggest (but not prove) a likely entry was via the #4 exhaust valves and I can accept as coincidence that the #4 exhaust valves were open in both engines as the time of water entry - after all, it is a 25% chance.

Why is the compression low? Pitted valve and/or seat, broken rings, bent conrod?
If you introduce some compressed air into the cylinder (say via the injector hole, it might be possible to hear where the air is escaping - manifolds, sump or nowhere if the conrod is bent. I'm not a diesel mechanic but there are plenty onboard CF who are and who can offer a more informed opinion!

As for all glow plugs to be dead on both engines - strange. Are you sure both engines are newish, hours, date of installation????

[Karanga]

Unfortunately, it is not possible yet to assume water is no longer getting in. The current assumption is that it is getting in via the exit (exhaust) system.
The plan is to flush several times with new oil and filters, while trying to work out how the water could get in.
The port motor elbow (not used since sailing to current anchorage) was uncoupled and several litres of water gushed out!!
These motors replaced the originals. They have now done 500 hours. I would consider that to be newish.

Originally Posted by Wotname

Thanks [emoji2]

Leaving aside the potential design issue causing water entry for a moment, can we assume water is no longer getting into the engine?

The compression numbers would suggest (but not prove) a likely entry was via the #4 exhaust valves and I can accept as coincidence that the #4 exhaust valves were open in both engines as the time of water entry - after all, it is a 25% chance.

Why is the compression low? Pitted valve and/or seat, broken rings, bent conrod?
If you introduce some compressed air into the cylinder (say via the injector hole, it might be possible to hear where the air is escaping - manifolds, sump or nowhere if the conrod is bent. I'm not a diesel mechanic but there are plenty onboard CF who are and who can offer a more informed opinion!

As for all glow plugs to be dead on both engines - strange. Are you sure both engines are newish, hours, date of installation????

[Wotname]

Originally Posted by Karanga

Unfortunately, it is not possible yet to assume water is no longer getting in. The current assumption is that it is getting in via the exit (exhaust) system.
The plan is to flush several times with new oil and filters, while trying to work out how the water could get in.
The port motor elbow (not used since sailing to current anchorage) was uncoupled and several litres of water gushed out!!
These motors replaced the originals. They have now done 500 hours. I would consider that to be newish.

Yikes, several litres is a lot!
Yep, 500 hours are newish - not a good sign for all the glow plugs to have failed. Sill, perhaps not related to the big problems - water and low compression!

Good luck and hopefully better guidance will be forthcoming soon.

[bharney]

anti-siphon valves are prone to failure which can cause backflooding of your engine. If you have one you can remove it and run a small diameter plastic hose to drain overboard and save yourself considerable grief.

[a64pilot]

Originally Posted by Karanga

Glow plugs were all dead(!) and replaced.

You know that could be it right there, especially if there were ever times when starting was attempted but abandoned because the thing just wouldn’t start but later was cranked.

[a64pilot]

500 hours pretty much eliminates the exhaust elbow if they are new.
Still think water is getting in through the exhaust, especially if your saying the exhaust hose was removed from the engine and water came out.

To the person that asked low compression is very likely due to corrosion of the cylinder walls due to water ingress, and I’d assume #4 cylinder may be closest to the exhaust elbow?