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Old 05-19-2022, 06:59 PM   #1
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FL 120 Raw water pump priming?

This one's kind of got me:
I replaced the raw water pump impeller and moved the sea water strainer about six inches closer to the engine. When I started the engine I couldn't get water pumping through the system. I'e done this several times before, drawing water from a five gallon bucket without any problems. Strainer and hoses were full of water but the pump wouldn't pump. It was only after I forced water into the intake hose (with a garden hose) that the pump would prime and now its fine.
Has anyone else had problems priming the original type Jabsco raw water pump?...Or even had the need to?
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Old 05-19-2022, 07:20 PM   #2
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Not Lehman specific, but some engines have a hard time priming with an air bubble right at the pump input. Especially if the impeller isn't lubed. I've had to pull the hose to the pump, pour water in and reconnect in the past to get an engine to prime.
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Old 05-19-2022, 07:38 PM   #3
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I have usually , after a raw water pump re/re, pulled the hose off of the strainer output hose and then filled that hose with water untill it threatens to overflow.
That way there is water for the pump to grab almost immediately.

I also flood the impeller with liquid dish detergent so there is a decent seat at the impellor vanes.

As suggest air in the hose may interfere big time especially if the vanes are dry.

Sometimes there may be a wear problem in the pump.
The back plate worn, the cam plate worn, or the cover plate worn. If the impellor does not fit properly it may simply scoot air around inside not developing any amount of vacuum to pull water and prime.

Any poorly sealed hoses between the intake and the pump may also allow air leakage which can defeat pump priming.

Soo's mention of the relative position of the RWP and the moved strainer may have left a hose clamp not quite snug enough.
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Old 05-19-2022, 07:40 PM   #4
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Since you moved the strainer. Wondering
Most pumps are below water line, is your strainer also below water line. Thru hull open.
No answer for you but look forward to the reason.
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Old 05-19-2022, 08:07 PM   #5
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If you take the output hose off the strainer and open the through hull does water flow our copiously? Having moved the strainer that is the first place to look. Anytime you work on something and something else changes go back to square one.
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Old 05-19-2022, 08:11 PM   #6
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I never had a problem with mine.

When I thought I did, I just left the pump cover loose, then opened the sea cock long enough to get a drip out of the pump. Close the seacock, tighten the pump cover, open the seacock and start.

Messing with hoses always equalled work in my book.
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Old 05-20-2022, 07:44 AM   #7
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In the 15 years I owned my Albin/Lehman 120 I never had to prime the pump. But that was with a upgraded Johnson pump and larger strainer. And it was hauled out and winterized each of those years.
One thing to check is the cover on your strainer. If it leaks air in it could cause this. I always greased the threads on the cover to make sure it sealed.
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Old 05-20-2022, 08:14 AM   #8
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Thanks folks for taking the time to offer suggestions.
I'm not sure I'll find the answer at this point but each post gives food for thought.
The boat is still on the hard and I'm prepping for the season.
I did pressure test by plugging the hose at the pump and putting hose pressure at the intake, so I'm confident there were no leaks before the pump.
One thing that occurred to me is that I changed out the exhaust elbow at the same time. Doing that drained water from the pressure side of the pump...? Maybe that had some affect?
Anyway...thanks again for taking the time to discuss.
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Old 05-22-2022, 03:54 AM   #9
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Just because shit does happen, I’ll relate that I once installed a new impeller that failed to pump water. After much head scratching and a little cussing, after the second removal discovered that the impeller was correct diameter, but was about a quarter inch too short!
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Old 05-22-2022, 06:56 AM   #10
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FL 120 Raw water pump priming?

Quote:
Originally Posted by kapnd View Post
Just because shit does happen, Iíll relate that I once installed a new impeller that failed to pump water. After much head scratching and a little cussing, after the second removal discovered that the impeller was correct diameter, but was about a quarter inch too short!


Along those same lines; i once replaced a pump upside down. Its in and out ports are on opposite sides. That wont work either.
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Old 05-22-2022, 07:46 AM   #11
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Can you leave the pump cover off and bump the engine? Twice I’ve seen where the pump shaft had failed and the impeller wasn’t turning. Not on Fore Lehman’s but it could happen.
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Old 05-22-2022, 04:49 PM   #12
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Quote:
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Can you leave the pump cover off and bump the engine? Twice Iíve seen where the pump shaft had failed and the impeller wasnít turning. Not on Fore Lehmanís but it could happen.
I am up and running now. Forcing water into the pump with a garden hose got her primed.
I did bump the engine with the cover off the pump to make sure that I had the impeller in properly. That taught me a little too: I found that, after I bumped it, the engine would rotate backward (maybe an eight of a turn?) and that would leave a few of the impeler blades pointing in the wrong direction until the pump spun up again. I've opened the pump cover in the past and wondered why the blades weren't all agreeing on direction.
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Old 05-22-2022, 05:24 PM   #13
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Quote:
Originally Posted by Mike GB32 View Post
I am up and running now. Forcing water into the pump with a garden hose got her primed.
I did bump the engine with the cover off the pump to make sure that I had the impeller in properly. That taught me a little too: I found that, after I bumped it, the engine would rotate backward (maybe an eight of a turn?) and that would leave a few of the impeler blades pointing in the wrong direction until the pump spun up again. I've opened the pump cover in the past and wondered why the blades weren't all agreeing on direction.
Thus why some of us laugh and giggle when some insist that you have to insert the impeller with all the blades properly aligned in the right direction.
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Old 05-23-2022, 06:06 PM   #14
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Old manuals recommend greasing the inside of the pump and cover when replacing the impeller. It greatly increases the pump suction and protects the new impeller from friction wear. Not the green way, I suppose.
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Old 05-23-2022, 06:14 PM   #15
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Quote:
Originally Posted by Lepke View Post
Old manuals recommend greasing the inside of the pump and cover when replacing the impeller. It greatly increases the pump suction and protects the new impeller from friction wear. Not the green way, I suppose.

Dish soap works pretty well as a green alternative. It's thick enough to help the new impeller seal while it all wears in, it's slippery, and it washes out pretty harmlessly. No risk of it hurting any downstream hoses or anything either like a petroleum product might.
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Old 05-27-2022, 01:42 PM   #16
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Quote:
Originally Posted by kapnd View Post
Just because shit does happen, Iíll relate that I once installed a new impeller that failed to pump water. After much head scratching and a little cussing, after the second removal discovered that the impeller was correct diameter, but was about a quarter inch too short!
Exact same thing happened to me on a Cummins 6BTA engine. Changed the impeller and the pump wouldn't pump. Tried all the tricks to make sure pump was flooded, spline on the impeller wasn't loose, etc. Finally called a local Cummins mechanic. Turns out that Cummins used two different pumps/impellers... for the older engines (mine), the impeller was the same diameter but about 1/4" thicker. He sold me the correct impeller and all was well.
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Old 05-27-2022, 02:43 PM   #17
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Do you know the number of hours the actual pump has run? If you do, call Brian from American Diesel and ask him how many hours you could expect before wear on the insides of the pump necessitates either a repair kit or replacement. (He did tell me but I can't remember)
I say this because I do about 900 engine hours/year and I had a pump lose prime while on the move. I saved a serious overheat as I have Borel exhaust temp monitors, but still gave a me a scare.
When I removed the cover, the impeller was sound, but wear behind the impeller on the wear plate inside the body was the culprit.
I'm wondering if you have some pump wear, which is giving you the issue of a 'weak prime'. If that's the case, you may need to take some action, because it will only get weaker.
You can buy a repair kit which has components that once fitted will bring the required tolerances back to spec..
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Old 05-27-2022, 03:33 PM   #18
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Do you know the number of hours the actual pump has run? If you do, call Brian from American Diesel and ask him how many hours you could expect before wear on the insides of the pump necessitates either a repair kit or replacement. (He did tell me but I can't remember)
I say this because I do about 900 engine hours/year and I had a pump lose prime while on the move. I saved a serious overheat as I have Borel exhaust temp monitors, but still gave a me a scare.
When I removed the cover, the impeller was sound, but wear behind the impeller on the wear plate inside the body was the culprit.
I'm wondering if you have some pump wear, which is giving you the issue of a 'weak prime'. If that's the case, you may need to take some action, because it will only get weaker.
You can buy a repair kit which has components that once fitted will bring the required tolerances back to spec..
Thanks for this. I did do a rebuild maybe two hundred hours ago, I'm not sure if I replaced that wear plate. I'm going to have to search through receipts. That sure makes sense. That exhaust alarm is definitely on my list.
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Old 05-27-2022, 08:33 PM   #19
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When I replaced mine it wouldn’t draw, so I primed it and away she went… but now my jabsco water pump has a drip when I shut down. I wonder if I had primed it initially maybe it would be dry like my previous one.
Best of luck
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Old 05-27-2022, 09:26 PM   #20
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My new impellers have a small squeeze pouch of glycerin included, instructions to lube impeller and housing before assembly.

Glycerin is cheap at the drug store.
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