Water retention in the impeller housing ?

B

baz

Well-known member
Joined
Jun 19, 2009
Messages
6,085
Fluid Motion Model
C-24 C
I'm curious to know if water is retained in the impeller housing when the engine is stopped and not running for several weeks ? I ask this, as I believe if water is not retained in the housing then when the engine is first started the impeller will be rotating with no water lubrication for a period of a few seconds. This has to be bad for the longevity of the impeller.

Of course if water isn't retained, there's not much that can be done presumably!

Does any one who has taken a Yanmar engine course know the answer to this I wonder ? (Mike-knotflying maybe and Howard-HRowland)
 
This was not discussed in the class. The only item regarding impeller lubrication was to use dish detergent on the new impeller when replacing. This helps in two ways, it makes it easier to slide the new impeller into the housing and provides a few seconds of protection on first start.
When the engine is stopped for an extended period I suspect the inside of the housing will stay wet even if most of the water drains back. Since we never hear of issues after engines sit for weeks at a time this must be enough.

I have not changed my impeller yet but will be soon, I have 175 hours on the clock. When others remove the cover for impeller change does much water drain out?

Howard
 
Howard: That's an excellent probing question about "When others remove the cover for impeller change does much water drain out?" The presence of water in this situation would tell us a lot!
 
I just changed my impeller last week, after the boat sat in inside storage for 6 months. When the housing pulley/impeller cover was removed I had a noticeable amount of water released from the impeller housing. As a reference I had closed my seacock before the boat went into storage, which may have helped retain water. What have others found?
 
I also had quite a bit of water drain out when I changed my impeller last weekend. The boat was in the water, so the seacock was, of course, closed. It had been several days since the engine had been run.
 
trailertrawlerkismet":2jdjvn6n said:
.......As a reference I had closed my seacock before the boat went into storage, which may have helped retain water........
Click to expand...

I expect that is significant but I also do not believe the impeller would dry completely, regardless. Think about how many vanes would have water trapped between them and the housing as the impeller rotates. Short periods (seconds, not minutes) of running dry will also not hurt the impeller. That is pretty tough stuff running in a smooth housing.

I would suspect that storage would not appreciably affect impeller life unless it was so long that the water evaporated and the boat was run on-the-hard with no intake water. (Or the rubber started to rot due to age. Probably many years in the dark like that. And who would let a Ranger sit that long?)

Now running the engine with the seaclock closed..... that's another matter. The trapped water would be expelled, the impeller overheat, and.......
 
I would think if an appreciable amount of water was retained, you would hear reports of broken impellers or housings due to freezing temps.

Jake
 
My experience was the same as others. I replaced mine while at the dock. Closed the sea cock and when I opened up the casing some water came out. Now when boating is over I usually close my sea cock and pour antifreeze (RV type) through the sea strainer and run it through the system until it exhausts. I leave the sea cock closed assuming the antifreeze will remain in the system and also act as a lubricant for the impeller. These are assumptions of mine and not necessarily fact.
 
From the posts so far it does seem as if water is retained in the impeller housing after the engine is stopped and remains there for some time.

This makes sense to me if the input & output ports in the housing are above the lower surface of the circular housing chamber. If so, then as I don't have my spare impeller at hand I will make the assumption that the two port opening are at least on the horizontal diameter line, the housing radius is 1.5" and the depth of the housing is 2.5". This then means 1/2 of the volume (excluding the impeller material) is some 8.5 cubic inches, or some 5 fluid ounces or some 0.6 cups of water.

So based on above and subtracting out half of the impeller material volume it would seem that as much as 1/2 cup of water remains in the impeller housing.

In addition, if the sea cock is left open (and even if it's not) some of the inlet piping leading up to the impeller housing will have water in it as much of it is at or slightly below the water line. I say this as my observation of my sea water strainer clearly retains water after the engine is stopped and the sea cock left open.

Thus, when first cranking the engine there's already 1/2 cup of water in the impeller housing and with a few impeller rotations (assuming it's fully intact) will quickly draw more water in. From this I would say that it only takes maybe 1 or 2 seconds for full water flow through the impeller housing to occur.

Now I'm also assuming that the only means for raw water to be circulating through the engine's coolant's heat exchanger is due to the impeller.

Good discussion.... thanks.
 
Well, from personal experience....on our R-25

We left the dock and headed out to sea without double checking the intake lever for the seawater. It took several minutes traveling at no wake speed for the impeller to spew back smoke out the exhaust. So there must be enough water in the system to keep it lubricated for any length of start up time.

After we saw the smoke, shut down the engine, opened the valve, restarted and all was fine. Shortly after replaced the impeller and it did not show any wear.

We had used a little dish soap on the blades when installing.

So, after our experience, I would not be worried too much about the volume of water in the system, as long as the valve is open to cool the engine.
 
Hmmmm.... Glad you were able to recover from that situation... Thanks for posting your comforting words about there being sufficient cooling water when starting the engine under normal conditions etc.

I assume your experience was not a test... 😉 Hopefully not. 🙂

BTW -- black smoke means... unburnt fuel (rich fuel mixture), residue from the impeller vanes being scorched by over heating (burning rubber like that from a burning tire maybe), the ECU going nuts trying to figure out fuel/air mixture due to excessive heat, or what ??????????
 
Jake, all the Tug owners I know in freeze up land use pink RV fluid to flush the sea water system prior to lay up - and the head, etc..
 
My tug was built in August 08.
Had a bit over a hundred hours on the engine before we took it to Florida for the first tug gathering there in 011.
I changed out the impeller before that trip. It was hard and some vanes were permanently deformed and starting to tear. Likely it would have failed in 15-20 hours or so (swag)
The bouncy rubber does not stay that way more than a few years even in the dark with limited running.
Since I put only a few hours on the engine each year, I am intending to change out the impeller every second year. Cheap insurance. It is on my punch list for this summer.
 
You must log in or register to reply here.

  • Tugnuts.com is the community hub for Ranger Tug, Cutwater, and Solara owners. Since its inception in 2008, the Tugnuts forum has grown into an active and thriving community of more than 9,000 members. It serves as both a meeting place for the best boating community online, and an invaluable archive of information.

  • User menu
Back
Top