Kubota N4.38 new install - hydro locked?.

[MarDeLea]

Just had a new Kubota Nanni N4.38 installed. After 17 hours we had a hydro lock on startup culminating in a complete rebuild. After the last passage the shut down procedure included raw water intake shut off. The exhaust hose from the mixer elbow has the water lock. The raw water strainer is slightly above water line. The exhaust is above waterline and it too has a loop in the exhaust hose above waterline. The engineers still wonder how this could have happened considering it’s a brand new motor and the raw water was shut off. For a possibility a anti-syphon valve was installed during the rebuild. Now the QUESTION how did the water seep into the cylinders? Through the exhaust valve - but how?

[skipperpete]

Possibly the volume of water in the exhaust to transom outlet combined with the water on the dump side of the vent loop exceeded the volume of the aqualock, if this is the case, you might be looking at another flooding. It is important to remove the hose between the mixer elbow and the waterlock at next shutdown and see how close to the exhaust inlet it gets. It can also be caused by the velocity of the water as it is dumped by the vent loop, especially if the vent is large.

[MarDeLea]

Thank you for your observation. Ill remove the exhaust hose for sure to see what the water level is. Hopefully ok.

[skipperpete]

I suspect by the engineering drawings that the vent loop can’t go in the usual position at the mixer elbow so if it’s on the raw water pump outlet on the front of the engine then almost the entire heat exchanger contents will drain into the mixer elbow, that’s a lot of raw water. What size waterlock is behind/below the exhaust outlet?
Shutting off the raw water intake will not help if this situation exists unless you shut it off while the engine is running to reduce the volume in the system.
Pete.

[bstreep]

Check your vent loop. Make sure some moron didn't put the little duckbill in backwards. FWIW, we bought a vent loop from Worst Marine, and didn't check ours. Fortunately, the Yanny is just fine.

[MarDeLea]

Thanks Pete for your insight. I’ll raise these points with the engineers. I’ll certainly be checking before startup. Thankfully it was all done under warranty
Cheers