Ford Lehman: replacing impeller on Jabsco water pump

I have twin Ford Lehman SP135's. The newly replaced impeller on the port engine has sheared completely. I have several questions, then I will add some details. Questions: 1) What causes impeller to shear? 2) Does it matter which direction the vanes are slanting at installation? 3) If it does matter which direction the vanes are slanting on installation, how to determine which is the correct direction?

Here's the story:

I motored from Long Beach, CA to San Diego. All systems operated perfectly. After 2.5 months in San Diego without running the engines, I cranked up and started heading out. Within about 2 miles, the alarm on the port engine sounded. The temp had reached 212. Shut it down and headed back to port. First Action: checked the pump; impeller looked ok, but replaced it anyway. Installed new impeller with vanes slanting the same direction as the old one. Second Action: called an old salty friend. He told me to check the seacock that feeds the port engine. Sure enough, it was encrusted with hard growth inside the seacock and in the intake recess beneath the screen on the wetted surface. Went under with diving gear and cleaned the intake. Inboard, cleaned the seacock with a screwdriver. It belched out hard growth then started to flow. Seacock lever operated smoothly. Third Action: Checked the raw water filter between the seacock and the pump. It looked clean, but opened it and flushed it out anyway. Re-assembled filter, hoses, etc. Headed out. Again, within 2 miles the port engine started overheating, but this time I was watching it and shut it down before the alarm sounded. Back to port. First Action: checked the flow coming out of the raw water filter, looked good. Checked the pump; discovered the impeller had sheared completely. Not a single vane was left intact. Since then I have talked with one mechanic who couldn't tell me what causes an impeller to shear, aside from old age. Also, he said it doesn't matter which direction the vanes are twisted on installation, it will correct itself. Also advised to lubricate the vanes with dish soap. The Jabsco replacement impeller kit comes with a supply of lubricant, which I used. As for the vane direction, the first time I mimicked the existing installation. But, now, the vanes are all missing, so I can't tell which is the correct direction. I'm assuming it would be the opposite of the flywheel direction, since the pump is geared directly to the flywheel. But, you all know what happens when we "assume."
Now that I am replacin the impeller for the second time, and I thought it would be wise to get some input beforehand. I hope there is someone on the forum who can advise me. Any advise will be appreciated.
Thanks for your interest.
GypsyGene

Three things will shear them. Run them dry, debris getting past your strainer, age. When you install an impeller it's good practice to put some dish washing liquid in there. Makes it easy to get in and it lubricates before the water arrives. With the soap in there no it doesn't matter which way it's bent.

The vanes will orient themselves as soon as the impeller starts to turn. While it's probably nice to put the impeller in with the correct vane orientation it is not necessary, at least not on the pumps I've had experience with which includes the original Jabsco pumps on our FL120s and their superior and larger Johnson replacements.

I have no clue why your brand new Jabsco impellers are shearing their blade. While their stuff is not the best, it's certainly good and shouldn't be doing this unless they've managed to crank out a bunch of defective impellers.

Make sure you don't have one too many wear plates inside the pump if your pump uses those. If there is one, it will be the flat plate at the rear of the pump chamber. The outer wear plate is usually the cover plate itself. The cover plate should be a tight fit down onto the blades of the impeller when you install it but you shouldn't have to apply a lot of pressure to seat it.

Make sure the pump is getting water almost as soon as it starts turning. A flexible impeller pump turning in a dry chamber can heat up and destroy itself in pretty short order.

And as Daddyo said, make sure there is no debris trapped in the chamber. Particularly hard debris like the hard growth you described.

(I wonder if that's a California thing. Our boat had a hard, crystalline growth in the port engine throughhull when we brought the boat up from California. Within a year it grew to the point where it began to restrict the waterflow. Diesel shop chipped it all out and it's never come back. The shop said they had seen this only a few times before, always on boats that had been brought up from California.)

And, I suppose it's conceivable you were sold the wrong impeller for your pump and the fit is off just enough to bind the vanes and break them off.

It's also conceivable that your replacement impellers have been really, really old and the rubber had started to harden up and deteriorate even though they looked okay. But I don't know enough about impellers to know if that's even possible with a new one.

Other manufacturers make impellers for the completion's pumps. I believe we used to use Johnson impellers in our Jabsco pumps until we changed out the pumps completely. Of course now we use Johnson impellers in the Johnson pumps.

Be aware the same Johnson pump that we put on our FL120s can go on the SP135. In fact we installed the 1" pump on our engines, which is the size recommended for the SP135. The Johnson pump usually put on an FL120 is the 3/4" pump. At the Johnson was backordered on the 3/4" pump and we needed pumps right away. So on the recommendation of our diesel shop and American Diesel we went with the 1" pump.

It was a great improvement to our engines. The waterflow is considerably greater which has knocked our transmission temperatures down a lot. The engine temps stayed the same because of the thermostats.

If you are leery of Jabsco impellers now, try a different brand. Talking to your diesel shop might shed some light on the problem, too.

No water supply or pumping against a closed system will quickly destroy an impeller. I suspect that your pump is still not getting any/enough water. If you have water-lift mufflers, can you hear the water "wooshing" out of the exhaust when the engine is idling?

One thing we were taught to do by a friend in the marine engine industry when we got our GB is to check the exhaust exiting the boat at every startup. In our case whoever isn't starting the engines goes to the aft deck and watches and gives a thumbs up if water starts exiting within the normal time after each engine fires and if the water volume looks normal.

It's also handy to have someone watch the exhaust at startup, particularly the first startup of the day, because if a component is starting to rust--- on our boat it would be the water injection elbows as the rest of the exhaust systems are fiberglass, rubber, and bronze--- rust will be apparent in the first gout of water that comes out the exhaust. If someone isn't there to observe that first shot of water this telltale will be missed.

This was instrumental in warning us that the exhaust systems that were on the boat when we bought it were living on borrowed time.

California is just the beginning of the growing crustaceans. The farther south into warmer waters the faster they grow. I have screens over my through hull fittings to the engines and every haul out they are removed, cleaned and painted.

My guess is that was an old impeller. They can run a little before breaking up if the rubber is fresh. Your problem now is to clean out all of those broken pieces before they clog up your engine's cooling exchangers, both fresh water, oil and transmission.

That can be a time consuming job. I'd backflush if possible and into a bucket so you can see all the pieces. Especially the heat exchangers.

Good Luck! Where are you in LB? Alamitos Bay or Shoreline?

For those with rubber impellers some where in an engine or noisemaker cooling system , one simplr solution is a Y stule strainer AFTER the pump.

Each time the rubbers die , simply cleaning the strainer catches all the chunks .

They may run $100 each , so boat assemblers do not include them on price boats.

UPDATE
First, thanks all who contributed. Excellent advice from each of you. Now, here's the latest: First Action: Replaced impeller with new Jabsco. Noticed that my pumps are Johnson (thanks, Marin), and the Jabsco package references "Johnson PN#09-1027B-9". So, next time I will be sure to get the Johnson part instead. Checked housing for additional plate, but it appears that the wear plate and cover plate are the same. Also found 2 small pieces or rubber trapped in the elbow tube. Used the lubricant that was supplied with the impeller. Second Action: Disassembled heat exchanger and oil coolers. Shined a bright light through; the oil coolers look very clean, with no debris, rubber or otherwise. The heat exchanger has screens on both ends, so no rubber or other debris there. HE looks worse than oil coolers, but still clear through all tubes. Blew out HE unit with high pressure steam, looks much better. Still wondering where the rubber debris might have gone. Third action: Starting re-assembly this afternoon. Will check back on this thread to see if anyone has added additional advice. Thanks all. GypsyGene

BTW: Capthead, I am still in San Diego, but will be back in Wilmington or San Pedro soon. Thanks for asking.

GypsyGene, I'm in California Yacht Marina in Wilmington.

Know it well. I will be at Island Yacht Anchorage #1 in May. Terry told me today that she has a slip for me. Hate the train noise, but it's a great place otherwise. Was there for 3 years before coming to San Diego. Keep in touch, we'll have lunch at the grill.

Sounds like a plan.

No affiliation with this company, but it looks like it could have held your impeller together despite running dry;

Welcome to Speedseal Technical Details

It doesn't fit my particular Yanmar, so I had to order their original impeller without the internal rotating disk.