IMPELLER FAILURE

[nzfisher]

Just a question regarding how critical it is to get impeller vanes out of the system. There were no parts in the impeller housing. Mine failed and all but 2 vanes were gone. Are they likely to have flushed through the system or are they going to impede flow of raw water? I have received varying opinions and of course I want to believe they are flushed out. Any reliable info? If they are likely to still be there, what is the easiest way to start removing them?

Thanks

 

[trailertrawlerkismet]

It very well may be that the missing parts have flushed thru your system however I'd go an extra step to satisfy myself, if it were me. Forgive me as I'm not at my boat so I'm speaking off the top of my head. There should be a hose coming off of the impeller housing where the water is pushed into, exiting the impeller. On other boats I've had and mind you I have not done this on my Yanmar yet, I've taken this hose off from both ends.....the impeller and to where it leads to. The reason for this is that there could be impeller vane pieces in the hose or in the housing it connects to on its exiting end. That's just if it were me and it could be overkill but as long as you're working in the area why not? Maybe someone else, who has actually done this on a Yanmar will speak up.

Jim

 

[baz]

A good question...

1) If the broken off vanes disintegrated into small pieces I suspect they would be flushed through and are long gone overboard.

2) Of course, it's really unknown if the broken off vanes disintegrated into small enough pieces to get.be flushed through the system.

3) If you've replaced the impeller, engine coolant temp stays at around 188ºF at all RPMs and you see plenty of water spurting out from the waterline exhaust port, I'd say you are OK.

4) I'm unsure how the heat exchanger is designed with respect for allowing things to pass through. If it has narrow passages then even small pieces could be stuck in there. The vane pieces will not degenerate over time and could be compromising the heat exchanger's operation for cooling the engine coolant liquid over time. But time will tell per item 3).

5) If the heat exchanger can be removed easily and examined somehow this would be useful in giving you some 'peace of mind'. Check with others here or contact a reputable Yanmar service to find out how easy/difficult removing the heat exchanger might be. Even if you remove the heat exchanger I wonder if you can actually see inside it for broken pieces of vane debris ?

6) I think you will need some expert advice on how to remove any remaining concerns you have with the failed impeller casting off pieces of its vanes. You say 2 vanes remained. How many vanes in total are on the impeller... I have a spare impeller on my boat so I can count them later I suppose.

7) I'm sure this event has happened numerous times for others, be that for Ranger Tugs or other boat models. Scan the web to see if you can get some answers on this issue.

8) Good luck and post back what you decide to do to resolve this remaining concern.

Thanks....

 

[HRowland]

The impeller pieces would have to be pretty small to flush through. Assuming you have a BY2 engine after leaving the pump the raw water flows first through the transmission oil cooler first (called hydraulic oil cooler in the engine manual). This is very low on the starboard side, next to the oil pan. Next is the charge air cooler (turbo intercooler) where the raw water flows through small tubes. After leaving the charge air cooler the raw water enters the engine coolant heat exchanger, and again the raw water flows through small tubes. After leaving the heat exchanger the raw water enters the exhaust elbow for discharge through the muffler.

As Barry said see how the flow out the exhaust looks and watch the engine temperature, you may get lucky. My temp indicates hotter than he stated, at low RPM the engine temp will be in the mid to high 180s but at high power settings will be 200F or a little higher. This has been consistant since new. This also depends somewhat on raw water temperature. Note that the engine thermostat does not fully open until 205F (it starts to open at 190F), so even at 200F the thermostat is not letting the maximum flow of engine coolant through the heat exchanger.

Also keep in mind that everything has tolerences. Even though we have nice digital readout of engine temp with one degree resolution the sensor is just a resistor that varies resistance with temperature. According to the service manual when testing the sensor at 212F the allowable resistance is 120 to 170 ohms, quite a range and not precise! Once you know what is normal for your engine you can be aware of changes.

Howard

 

[baz]

There are 8 vanes on the impeller. So you've lost 6 vanes which presumably have been ingested into the raw water cooling system, and likely lodged somewhere if not blown through to the exhaust outlet. I talked with my local boat yard technician about this and he indicated apart from the initial outlet pipe from the impeller housing the water passages are quite narrow especially in the heat exchanger portion that cools the engine's fresh water coolant. As Jim mentioned, maybe the vane pieces are located in the first portion of the impeller housing exit pipe. It's hard to believe the missing vanes have been chewed up into small enough pieces and hopefully they are in the pipe that Jim mentioned. The pieces are likely to be laying in line with the pipe and not seriously obstructing water flow... Take Jim's advice and pull that pipe out and check inside of it.

 

[HRowland]

Here is a picture of the exit side of the raw water pump that Barry mentioned.



This is the first place the raw water goes, the transmission gear oil cooler.



Howard