Yanmar 1GM10 Impeller

[TerryO]

Has anyone experienced overheating on a 1GM10 due to the impeller vanes "flipping" on shutdown. I had just operated the engine for over 2 hours at higher RPM due to rough weather and everything worked perfect. I shut the engine down at the waste pumpout dock and after start up the engine overheat warning sounded. After shutdown I removed the water pump cover and confirmed good seawater flow. Then I noticed that the vanes on the impeller were all flipped the wrong way and were not pumping water. I know for sure that the impeller has been installed correctly and the engine had run for several hours just fine. I removed and installed the impeller correctly and the overheating issue was solved. I read on a forum from England that the engine will sometimes snap backward on shutdown reversing the impeller vanes. In my case at least the vanes did not flip back to the proper running position after startup. The impeller only has about six hours running time.

[Joe Myerson]

Terry,
I'm not sure that I've ever heard of the vanes "flipping" like that, but I would suggest that you replace the impeller pronto. I had overheating problems, and the impeller looked good, but in fact the vanes had broken loose from the spindle, so they did not always turn.

While you're at it, invest in a SpeedSeal, so you can change your impeller without having to use a wrench.

Just suggestions, of course.

--Joe

[TerryO]

Thanks Joe,
I did check to make sure the centre bushing was still bonded. I have a spare in case. I just received my Speedseal kit in the mail about a week ago. Nicely built parts. Ironically I went to install the cover kit the day before the overheating episode and the thumb screws were too long to seal the plate. I contacted Speedseal and they said that in a few cases Yanmar has not been consistent in the depth of the tapped water pump holes. They offered to send shorter thumbscrews but I will just take a 1/16 or so off of them.

[Sea Hunt Video]

Terry:

The diesel mechanic who has done a few jobs on my 1GM Yanmar was highly recommended to me by several friends at the local sailing club. I have found him to be very knowledgeable. He taught diesel mechanics for several years.

At a diesel workshop he conducted at the local West Marine store (one of the things I really like about WM is their seminars/workshops ) someone asked him about the vanes on the impeller accidentally being positioned in the wrong direction when replacing an impeller. He said that was a myth and that it cannot happen. He demonstrated with a water pump and impeller with no water. The vanes automatically "flipped over" in the direction of water pick up. He repeated this several times.

I have no personal knowledge or insight but I trust this guy's knowledge and expertise.

I too have the Speedseal. It is well worth the moderate cost.

[sharkbait]

Do not forget to pre-lube your new impeller with a water soluble material (vaseline).

[Steve Laume]

Do not forget to pre-lube your new impeller with a water soluble material (vaseline).

I have heard this advice before and have always wondered why you would use water soluble grease. I understand the need to have some lubrication in there to take care of the impeller before it sees any water but what is the reasoning for using a lube that will then disappear? The water pump on Raven has a grease cup on the side that allows me to periodically tighten it up to add more grease to the impeller. Whenever I change the impeller I apply a good bit of grease to the entire housing and the cover. This is not water soluble grease. I really want the stuff to stay in there.

This is a good thread. I always worried that I might put the impeller in with the vanes flipped the wrong way. It sounds like they will take care of themselves in this regard.

In general, the raw water pump is a very simple device and tends to be rather fool proof, Steve.

[TerryO]

Thanks for the good discussion guys.
An additional point I didn't put in my original post:
-When I removed the impeller cover and saw that the impeller fingers were pointing the wrong way I grabbed the manual starting crank, actuated the decompression lever and turned the engine over. Sure enough the impeller continued to rotate in the normal direction with the fingers pointing in the wrong direction. The impeller came with the boat so I wonder if maybe the rubber was not flexible enough to allow the fingers or lobes to flip into the proper position. When I get a new impeller I am going to try it again to see if they will orient to the proper position when the engine is rotated.

As far as lubricating the impeller with water soluble grease or silicone I am guessing that they do not want a petroleum based grease to break down the rubber in the impeller. However I also recognize that there are various materials used to make impellers. The Johnson impeller I installed is also used in Johnson pumps for transfer of fuel (Nitrile) so it wouldn't be an issue. Better safe than sorry though.

The lubrication should really only serve a purpose on initial startup when there is no water present to lubricate and cool the impeller. Not really an issue on my 25D either since the seawater inlet is basically at the same level as the pump and the impeller floods as soon as the seacock is opened.

[JWSutcliffe]

Don't agonize over the impeller vane orientation. Every raw water pump I have had over the years has sufficient squeeze on the impeller vanes to pump properly regardless of vane orientation. The vanes may kick back to the "backwards" orientation on shutdown, but will pump as long as they are all in place. Overheating problems are virtually all due to other causes. For example, after replacing my exhaust system last week I had to drain down about half the capacity of my coolant loop. I had an overheat incident today, which was due to a combination of trash in the raw water strainer and air bubbles trapped in the fresh water side of the cooling system. It took cleaning the strainer and about 2 hours of "burping" the fresh water side to get all the trapped air out to get the coolant temperature down to 180F at all operating conditions. It just takes time and patience to sort it all out.