Huge amount of water in Yanmar 1GM10 lube oil

[theBotanist]

Hey guys, I was going to take my boat out for the first time this year after replacing the packing in the stuffing box. I went to do a preliminary engine check before doing so, and I'm glad I did because when I removed the dipstick to check the oil the level of liquid was overflowing from the dipstick port and looked watery. I siphoned the liquid out and got nearly a gallon, over half of which was water. I consulted the user manual and service manual that came with the motor and was unable to determine what would cause such a huge amount of water ingress or what I might need to do (aside from the oil and oil filter replacement). It's a rebuilt Yanmar 1GM10 with about 450 hours on it, and when I ran the engine last year for several hours at a time there was no indication anything was wrong (no warning lights and no weird noises or colored smoke). It's been sitting since then which I know is bad for the engine but I'm not sure if that in and of itself would be the cause. I've read common reasons for water ingress in the lubricating oil are blown head gaskets or water getting splashed into the exhaust. The latter seems more likely since the exhaust sits very close to the waterline and can be dunked any time large waves or wake rock the boat. So I guess with that my question is what can/should I do to get the engine to a point where I can try and start it (assuming it's even salvageable)? I've changed the oil and replaced the filter, but I'm not really sure about next steps. I've read about the damage hydrolocking can do, so I want to be sure water has at least been purged from the piston before I try starting it. Thanks for the help!

[Wotname]

Yikes - that much water is not good - but you know that already.

The engine sitting unused did not cause the water ingress. The two most likely sources will be via the exhaust or failed seals in the raw water pump. The volume of water suggests the exhaust is more likely than the raw water pump.

1. DO NOT TRY TO START THE ENGINE!!!!!!
2. Change oil and filter.
3. Remove exhaust hose from the mixing point.
4. Close raw water inlet seacock.
5. Operate the decompression lever.
6. By HAND, rotate the engine though say 10 cycles. This should push most of the water out of the cylinder through the exhaust valve. Note, the exhaust valve remains slightly open while the decompression lever is activated.
7. Spray any de-watering fluid (WD 40 etc) into the intake manifold while rotating the engine by HAND (still decompressed). Do this for another 10 cycles
8. Assuming the engine 'feels' OK, e.g. no more water etc spin the engine over with the stater motor (still decompressed) for say 3 or 4 seconds.
9. If still OK, return the decompression lever back to normal (run) position. Operate the fuel stop lever, and spin the engine over with the starter motor for another 3 or 4 seconds.
10. If still OK, return the fuel stop lever to normal (run) and try for a normal start. If the engines fires and runs, stop it after a few seconds.
11. Refit exhaust hose and open raw water seacock.
12. Start the engine again and run for a few minutes in neutral at low rpm (say 1500). Check for normal operation of cooling water through exhaust.
13. If still OK, run the engine for say 20 minutes under load (tied to dock) over 1500 rpm.
14. If still OK, replace oil and filter again.

[Wotname]

Opps - I forgot - you will need to check the mixing elbow for integrity. Do this at step 11 above.

I.E.

11. Confirm by inspection the mixing elbow is serviceable and if so, refit exhaust hose and open raw water seacock.

[theBotanist]

Sorry it took so long to respond, and thanks for the step-by-step procedure! I was thinking I'd have to pull the fuel injector but operating the decompression lever is much easier It definitely seems that the water entered from the exhaust as it started dripping from the mixing elbow before I had it fully unbolted. After following the steps I was able to start the engine and it ran with no warning lights and no funny noises. Now I just need to figure out how to prevent water from going so far up the exhaust.

[Wotname]

That sounds positive

The water might be coming back up the exhaust hose though wave action and over-filling the waterlock. It depends a lot on the exhaust design. Designed well, wave action will not affect the engine; poor design, anything can happen.

However the water might be entering by a failed mixing elbow. See attached picture. If the internal cast web has failed, water will enter were the yellow lines are.