Gas genset ingests raw water

[schnarel]

Okay folks, I need your help diagnosing a genset problem.
Four years ago when I first purchased my boat the genset would not start. We determined that there was water in the crankcase. We did a few oil changes to flush the water and also did a tune-up (plugs, rotor, dist cap, plug wires, etc.). Following this service the genset has been working reliably, seeing about 100 hours of use over the last few seasons.

This summer the genset again started ingesting water into the crankcase. After changing the oil the engine ran fine, but was not getting much raw water flow so I replaced the impeller on the raw water pump. There were several missing vanes on the old impeller, but I'm fairly sure I got all the pieces. The genset started and ran fine.

A week later there was water in the crankcase again. This time I replaced the anti-siphon valve in the raw-water-to-exhaust-elbow hose. I cranked the engine between oil changes (three complete oil changes) but the engine would not start. I should point out that I pulled plugs before cranking the first time, so I'm reasonably sure I did not leave water in a cylender and break a piston. The engine seems to be fuel starved.

A couple of weeks later, the genset again had water in the crankcase even though the genset had not been run! Looking down the throat of the carborator, I see a lot of scale perhaps blocking the fuel. I will pull the plugs again and change the oil again. I will use carborator cleaner to flush the carborator throat or rebuild the carborator if that does not work.

But the fundamental problem is the water in the crankcase. I'm pretty sure that it's raw water since I keep the fresh water pretty green with antifreeze. Not only does the water pumped from the crankcase not look green, but neither does the fresh water level go down.

It is possible that the new antisiphon valve is defective, but how could the siphon have started when the engine was not even run?

This is getting old. If you have any ideas please let me know!!
Thanks for your help.
Chip

Boat is a 1986 Sea Ray EC 390
Engines are 454 cu in Crusaders
Genset is a Westerbeke 8kw gas (original with boat) with about 500 total hours.

 

[PlayDate]

Chip,

The water issue is the right one to focus on. I'm thinking a defective exhaust manifold or the water muffler has some restriction which is backing the water up and into the exhaust ports. That is the only way for raw water to enter the engine.

Disconnect the exhaust hose from the manifold (I know it is a pain) and with a dock hose, fill it with water. It is important to hold it at the same level that it normally attaches to the exhaust manifold. You will know pretty quickly if there is a blockage in the exhaust.

The only way to check the exhaust manifold, is to remove it from the engine and inspect it.

Let's start there and get that resolved and then we can move on to the carb. (I'm guessing we have a fuel pump issue if it is original).

-John

 

[tobnpr]

Far as I know your raw water pump is belt driven, and I don't think you have an oil cooler (I don't on my 8kw diesel), so I can't think of any other way for raw water to find it's way into your engine- when it's not been run- other than the exhaust manifold as John said.

I *think* a slow leak could cause your symptoms. I had a slow leak from a riser on the 350ci engine in my Chris. One day I went to start her at the dock and she was hydrolocked. After pulling the heads and looking at a couple of the valves it was obvious that there had been some seepage there for a while (rust). The engine continued to run until the riser failed while the boat was sitting at the dock and the "seepage" turned into a flood. I'm not sure why your cylinders aren't filling, unless the leak is in such a spot that it can run right into the crankcase without that happening.

I would pull the manifold and inspect. In any case, you should try to resolve this quickly. This isn't doing your bearings any good.

 

[schnarel]

Thank you both for your comments!

The genset engine is freshwater cooled so if the water in the crankcase was coming from there wouldn't that water be green and the freshwater level go down in the reservour? Neither of those is happening.

I did pull the exhaust hose to the muffler. That hose was full right up to the elbow at the rear of the exhaust manifold so I assume that water is backing up. The muffler is a "water lift" type. I think it requires some pressure to push the water through, but there could be a blockage. I guess I have to tear that apart next.

The raw water pump is belt driven. Water seems to be coming in whether the genset is run or not. The thru-hull is about a foot forward of the transome in the aft bilge well. Could the pressure there (esp. with trim tabs down) force the water past the raw water pump if the genset is not operating? I replaced the impeller, but perhaps I need to inspect that again, or run the boat with the exhaust hose disconnected to see if water is coming through.

Thanks again for your suggestions.
Chip

 

[fc3]

You should have a flush type of though hull, not a scoop type. Ensure that someone doing maintenance on the boat didn't install the wrong type of inlet on the though-hull fitting. Other than that, sounds like you are doing the right things.

Note that the Mitsubishi three cylinder engine has very tight clearances. If one connecting rod is even slightly bent, all hell will break loose in the engine.

Best regards,
Frank C