impeller in cummins generator

[bevis]

We've only got 60 hours on our generator and we have gone thru 4 impellers. The impellers are damaged by low water flow and have to be changed. Have others had this problem? Is there a better impeller? Contacted global marine and they do not make an impeller that fits my generator. Am considering changing from a 3/4 inch sea strainer to a 1 inch to assure water flow. Any ideas, oppinions or advice?

 

[R Baker]

I understand frequency of impeller replacement to be a problem in other generators as well. In the cummins-Onan the water pump is on the top and cooling water drains from the system when shut off. One solution I've read of, is to install a backflow preventer in the line to keep water from draining. Or, You could shut the intake after shutting down the genny.

 

[Doc]

I have the same problem with my new Onan (less than 5hrs) Since it was on a lift before I bought it and now is on my lift, I think it looses prime (as my AC does) therefore dry impeller. I am going to start closing all my seacocks, including engine, before lifting boat. I presume people who trailer their boat would have similar problems.

 

[R Baker]

The Onan installation is such that the cooling water line goes all the way around the engine, as the thru hull is on the opposite side from the Onan. The length of the hose if shorter might not cause the impeller to run dry for so long . Perhaps the Washdown supply and generator supply could be switched. Any thoughts ?

 

[R Baker]

Post script..... Sure enough all this discussion about Onan impellers; well mine shut down twice - 7 flashes, lack of cooling water flow. First I checked the strainer - basically clear, a very small indication of weed; then pulled the impeller - it was fine; then disconnected the strainer - the inlet hose was clogged with weed that did not get into the strainer. So in the future that will be the first place to check. I will also investigate a better strainer.

 

[bevis]

I have not been able to get a response from andrew on the 5/8 sea strainer as being common practice .my sea strainer is on the port side same as the intake as the generator .i did change it out to a 3/4 sea strainer there is a noticeable difference in water flow hope this fixes the problem going out for 4 days this weak will let you know .

 

[hughesdave123]

I replaced that tiny little strainer 2 season ago , and haven't had issue since.

 

[R Baker]

Hughesdave
Replaced your strainer - with what, please ?

 

[bevis]

same kind same make 3/4 inch instead of the 5/8 and all hose up to 3/4 id

 

[hughesdave123]

Hughesdave
Replaced your strainer - with what, please ?

just a larger one I found at westmarine.
I had to anyway , the old one cracked. but I was chewing up impellers up until I changed it.

 

[R Baker]

Sorry to belabour this...on my 29, the supply line to the strainer is 3/4 and from the strainer to the Onan is 5/8. It would appear my strainer is 3/4 with the outlet side crushed a bit to accept the 5/8 line. This strainer is wholly inadequate as it is easily choaked with weeds. I plan to install a strainer more like the engine one - perhaps a Victoria.

 

[Dale777]

I too have had my Cummins Onan 5Kw Genset inpeller require replacing with very few engine hours on it. In checking on the problem, I found as others have noted on this forum that the impeller is at the top of the engine, so there is the chance that the supply line can run dry after trailering or after boat storage.

This problem has been discussed at http://www.cruisersforum.com at this link:

http://www.cruisersforum.com/forums/f14 ... 24001.html

This comment in the cruisersforum about a check valve seems topical:

"I just put a check valve in the intake line. I was only getting about 50 hours out of my impellers before I put it in. I got about 600 hours out of the first one and am approaching 400 hours on this one. Since I used to go through a lot of impellers I still have 3 or 4 spares on board. I got brass check valves from West marine. I was afraid they would not last long, being brass, so I have a spare on board, but I'm at about 1000 hours and the check valve is still going strong. Also the check valve is well above the water line so if it lets go I won't loose the boat. "

 

[Connerkip]

After putting in the check valve, what speeds do you run the boat while the generator is running? I too have gone through impellor but I run at 16 knots. I when I was doing this, I was not on a lift or trailering.