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Old 11-12-2009, 09:58   #46
Jud
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Jud......someone is blowing smoke....page 38 gives the outputs at various rpms

http://www.johnson-pump.com/JPMarine...010_US_web.pdf
I was just looking at that, and it confuses me. My pump is in the F35B series at the top of the page. I don't understand why there are three different lines of gpm numbers for each RPM. E.g., for 2500 RPMs, it gives 5.4, 5.2, 4.5 gpm. Is each gpm output is for a certain input pressure or something? (I'm a layperson, so bear with me!)

In any case --you're, the numbers don't sync at all with what Johnson just told me. They emailed me the output graph on the following page of the catalog, which is what the guy was looking at when on the phone with me. 10 gpm at 2500, which is what he told me, doesn't look right at at all. This is getting way too confusing...I think I'll call them back to see if they can clarify: I want to understand this properly.
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Old 11-12-2009, 10:27   #47
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The Column to the left refers to head pressure. I.E. How high will the pump be pushing the water. The higher the water has to go...the less volume it will put out.

Have you ever had an impeller lose it's vanes in the past?

If so, it is very possible that pieces have lodged in the piping...upstream or down stream.

Usually at the first bend.
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Old 11-12-2009, 10:49   #48
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Have you ever had an impeller lose it's vanes in the past?

If so, it is very possible that pieces have lodged in the piping...upstream or down stream.

Usually at the first bend.
Good Point....

Happened to me once, they ended up in the heat exchanger, luckily none in the tubes...
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Old 11-12-2009, 13:03   #49
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Hook up an ordinary garden hose to the hose to the input side of the pump using radiator clamps and turn on full to backflush the intake side of the system to make sure there are no weeds or whatever on the intake side of the pump. I once had a low flow problem which persisted after cleaning the filter--which was not plugged. A friend showed me how to clear the input to the pump and problem went away.
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Old 11-12-2009, 20:19   #50
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The Column to the left refers to head pressure. I.E. How high will the pump be pushing the water. The higher the water has to go...the less volume it will put out.

.
OK, this makes sense to me now --at different pressure heads (how high pump is), the pump's output varies. The table gives an example of three different pressures. At 2500 RPMs, the highest RPM given for the pump, pump water output at the three different pressures given would be 4.5, 5.2, or 5.4 gallons per minute. According to the graph with output curves on the next page of the catalog link you posted (and according to the guy at Johnson I spoke to), the pump I have (and most impeller pumps) are designed to put out less water after a certain RPM. In this case, the pump's max. output is at 2500 RPMs and basically varies between 4.5 and 5.4 gpm. After that RPM, output begins to decrease.

So...drum roll...the other day, I measured my pump output at max. RPMs for my engine, 3200, and collected 4.5 gallons of water in one minute: 4.5 gpm. I assumed, based on specs for similarly sized engines around that RPM, that 4.5 gpm was low.

In fact, however, based on the numbers from Johnson, 4.5 gpm at 3200 RPMs may well be OK, since pump output goes down from a max. output of between 4.5 and 5.4 gpm at 2500 RPMs. Which is a more normal running RPM for my engine.

So...final drum roll...if I want to have a better idea of how well my pump is working, I should measure pump output at 2500 RPMs (and not 3200) --and presumably it will be between 4.5 and 5.4 gpm, per the specs from Johnson. Any less, and it suggests the pump isn't putting out enough. (However, of course, I have to realize that these numbers from Johnson are "laboratory" numbers and don't necessarily reflect real conditions...! Their words. )

In any case, doing a bucket test for one minute at 2500 RPMs (instead at engine max. RPMs of 3200) should give me a more better sense of whether my pump is putting out enough. Then I can put this damn water pump out of my head and look at the rest of the cooling system!
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Old 11-12-2009, 20:32   #51
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Jud, Yes that would be good...put the pump back in. Then start at the raw water inlet...and work your way back, one step at a time..

If you change too many things at once, you may solve the problem but not know what the culprit was. for instance, don't change the stat and the impeller at the same time.....

keep us posted...good luck
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Old 11-12-2009, 20:46   #52
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Also -I just changed my anti-freeze the other day, so that's brand new.
.

I haven't read all the responses so mine may be entirely off base, but check to make sure that there is no "air lock" on the fresh water side of the heat exchanger.
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Old 12-12-2009, 12:21   #53
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OK, this makes sense to me now --at different pressure heads (how high pump is), the pump's output varies. The table gives an example of three different pressures. At 2500 RPMs, the highest RPM given for the pump, pump water output at the three different pressures given would be 4.5, 5.2, or 5.4 gallons per minute. According to the graph with output curves on the next page of the catalog link you posted (and according to the guy at Johnson I spoke to), the pump I have (and most impeller pumps) are designed to put out less water after a certain RPM. In this case, the pump's max. output is at 2500 RPMs and basically varies between 4.5 and 5.4 gpm. After that RPM, output begins to decrease.

So...drum roll...the other day, I measured my pump output at max. RPMs for my engine, 3200, and collected 4.5 gallons of water in one minute: 4.5 gpm. I assumed, based on specs for similarly sized engines around that RPM, that 4.5 gpm was low.

In fact, however, based on the numbers from Johnson, 4.5 gpm at 3200 RPMs may well be OK, since pump output goes down from a max. output of between 4.5 and 5.4 gpm at 2500 RPMs. Which is a more normal running RPM for my engine.

So...final drum roll...if I want to have a better idea of how well my pump is working, I should measure pump output at 2500 RPMs (and not 3200) --and presumably it will be between 4.5 and 5.4 gpm, per the specs from Johnson. Any less, and it suggests the pump isn't putting out enough. (However, of course, I have to realize that these numbers from Johnson are "laboratory" numbers and don't necessarily reflect real conditions...! Their words. )

In any case, doing a bucket test for one minute at 2500 RPMs (instead at engine max. RPMs of 3200) should give me a more better sense of whether my pump is putting out enough. Then I can put this damn water pump out of my head and look at the rest of the cooling system!
OK, well, just did another bucket test @ 2500 RPMs --according to the specs, the RPMs at which I should expect max. pump output. Output was about 4.25 gpm. Seems to suggest the pump is not moving enough water (earlier test @3200 RPMs, max. engine RPMs, which I thought would produce max. pump output, was a bit more, about 4.5 gpms)...so, finally, it appears (I remain skeptical!) that the pump's not putting out what it should. (There are no blockages on the suction side: I checked.)

Gonna bring it to a pump specialty shop for further testing/diagnosis before looking at anything else. Maybe it's an obvious pump part that's worn out: the back plate, or the cam --either of which can, I'm told, lead to water bypassing the impeller instead of being pumped by it. The engine is 20+ years old and I don't know if the impeller pump has ever been rebuilt. (It might have been, since I bought the engine rebuilt, but maybe they didn't do that part.)

Stay tuned . Thanks again for everyone's insights and help on this...a real learning experience. (I want a new engine for Xmas )
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Old 12-12-2009, 14:29   #54
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RPM/GPM
700/1.4
900/1.8
1400/3.0
1750/3.7
2000/4.2
2500/5.4

Assume that the pump has never been rebuilt.

If you have a new impeller....put that in first....one can't look at an impeller and pronounce it ok....if the brass center piece has loosened, you can't tell. At low RPM it make work fine ....at higher RPM it will slip.

You can get a rebuild Kit from www.depcopump.com
The guys there are very helpful, tell them what you believe your pump is not doing.
Make sure you order the o-rings.

Are you still making the measurement off the stern? If so, try disconnecting the hose as it goes into the exhaust elbow. Run the engine for a minute and see if you get the same flow.
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Old 12-12-2009, 17:12   #55
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Before you get too carried away check the through hull for barnacles or weed.
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Old 12-12-2009, 17:33   #56
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I haven't read all the responses so mine may be entirely off base, but check to make sure that there is no "air lock" on the fresh water side of the heat exchanger.
And that's the reason Yanmar puts two air bleed valves forward in the freshwater system.
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Old 12-12-2009, 18:14   #57
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RPM/GPM
700/1.4
900/1.8
1400/3.0
1750/3.7
2000/4.2
2500/5.4

Assume that the pump has never been rebuilt.

If you have a new impeller....put that in first....one can't look at an impeller and pronounce it ok....if the brass center piece has loosened, you can't tell. At low RPM it make work fine ....at higher RPM it will slip.

You can get a rebuild Kit from www.depcopump.com
The guys there are very helpful, tell them what you believe your pump is not doing.
Make sure you order the o-rings.

Are you still making the measurement off the stern? If so, try disconnecting the hose as it goes into the exhaust elbow. Run the engine for a minute and see if you get the same flow.
Thanks --I did put a new impeller in when I re-tested output @2500 RPMs this morning. I was looking for output between 4.5 and 5.4 gpm (which the catalog specs have for different pressure heads for the pump --the list you put above is for the lowest head, right? .3 bars) Anyway, I got less than even the lowest spec --lower than 4.5 gpm with a new impeller, so something's up. This was measurement directly from the pump.

I will check at the exhaust elbow hose connection tomorrow. But it's looking strongly like the pump is weak (and there are no problems on the suction side or barnacles, etc. fouling through-hull, etc. I've looked at everything upstream of the pump, including sea strainer, hoses, and through-hull intake (and transmission, which is sea-water cooled --sea waters passes through tranny after entering boat and before going to pump)
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Old 12-12-2009, 18:53   #58
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I belive you mentioned you have a speedseal plate.....Is there a possibility that the gasket/o-ring is damaged?

From what I have gleaned so far....it looks like the pump.....

There may be a leak at seal, lipseal (inside pump) this could be allowing air in at higher RPM......and while we are at it, take a look at the gasket on your stainer.....

BTW where are you located?
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Old 12-12-2009, 19:04   #59
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Thanks --I did put a new impeller in when I re-tested output @2500 RPMs this morning. I was looking for output between 4.5 and 5.4 gpm (which the catalog specs have for different pressure heads for the pump --the list you put above is for the lowest head, right? .3 bars) Anyway, I got less than even the lowest spec --lower than 4.5 gpm with a new impeller, so something's up. This was measurement directly from the pump.

I will check at the exhaust elbow hose connection tomorrow. But it's looking strongly like the pump is weak (and there are no problems on the suction side or barnacles, etc. fouling through-hull, etc. I've looked at everything upstream of the pump, including sea strainer, hoses, and through-hull intake (and transmission, which is sea-water cooled --sea waters passes through tranny after entering boat and before going to pump)
Where are you measuring the RPM. Is the pump geared 1-to-1 with the tach?

Paul L
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Old 13-12-2009, 06:49   #60
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The pump parts wear. Side plates and the radial cam that flexes the rubber. Even with a new impeller, excessive wear on the metal parts will cause bypass leakage. The bearing may go also and reduce the impeller deflection= less volume.

Maybe new pump time.
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