hydrolock shaft seal

Hydrolock root cause found!

I finally figured out why the engine hydrolocked. Check out this image of the port engine first. There is a water line that runs from the shaft seal near the bottom of the photo that runs all the way forward, near the vented loop, and then comes back forward until it joins the pressurized water that is headed to the exhaust elbow (that connection is hard to see in this photo). The thing to note is the large loop toward the top of the picture. The point of this loop is to reduce (but not eliminate) the chance of a siphon starting.

The intent of this line is to feed some of the seawater from the engine into the shaft seal. Although this sounds like a great idea, it’s actually terrible. Imagine what happens when the pump stops. The line is full of water, and stays full. The exhaust elbow is just barely below the waterline. This causes a siphon, filling the exhaust system with water over time. This creates a lot of back pressure, making the engine harder to start. Enough attempts to start it and now you’ve got water backing up into the exhaust manifold….

The situation is far worse on the starboard engine. Bay Marine replaced this line, and all of it is below the waterline. So, it doesn’t even need to make a siphon -- you’ll just get some natural flow from the seal into the exhaust system. I have a photo of the starboard engine but I’ll save that for another day.

The silver lining

On the plus side, this forced me to pull all the injectors to get the water out of the cylinders. Since I haven’t done that before, I was able to quickly get some help from a local mechanic. When the injectors were pulled, the pre-ignition fitting was actually cracked on one of the cylinders. See if you can spot the crack in this blown-up photo. This injector would have failed soon. Unfortunately, this part is like $183. I hate you Yanmar. These can’t cost this much to make, and if you buy 3 of them, you’re almost at half the cost of the whole cylinder head assembly. And, the same part from a tractor supply place, is only about $40.

Anyway, I had the injectors serviced while they were out. They were just a little dirty according to Diamond Diesel, who charged me only $100 for a pile of cleaning labor and testing.

I really want to pull the injectors from the port engine, but I really don’t have time, with two weeks remaining. I am going to check the port side exhaust elbow though for signs of wear.


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