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Old 07-11-2015, 10:34   #16
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Re: Raw Water Pump Woes

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Originally Posted by Wotname View Post
You have covered almost everything already but I reckon the problem will be points 7 or 8.

You must remember the impeller must seal on three surfaces; the vane tips (obvious) and each side of the impeller (ie against the pump body and the cover plate). Any gap between the sides of the impeller and the body or cover seriously limit pump performance. You can get away with some wear but not much!

Your nearly new O ring might not be compressing enough especially with one screw missing or perhaps the wear / scoring has increased by a small margin.

In a pinch, I would try lightly facing the cover with some very fine wet & dry paper using a good flat surface (port glass???) and re-assembling without the O ring, just using some thin non hardening gasket sealant. Dunno what's in your area but Permatex make a few types

Or reversing the cover (suitably cleaned), again using a fine smear of sealant.

If that works, try refitting the O ring and check again.

Good luck
the above is a good start. altho I wouldn't use sealant, do put silicone grease on the O ring tho. Make sure there is nothing in the hose off the pump to the exchanger and/or Try putting some grease in with the impeller and see if that works. if it does resurface the plate cover as above. I've ran into this issue on my last Yanmar. It doesn't take much ware to lose tolerances on the matting surface from impeller to "ware" plate ...Ie... cover plate. If the groove is too deep flip the plate and lap it smooth on the other side. Use a figure 8 motion on some 320 wet n dry sand paper laying on a flat piece of wood or equivalent surface. Shake the residue off the paper frequently. A spun hub on a bolt through would be pretty obvious, at a glance. a missing screw isn't that big a deal, best to be near the cam if possible.but if it's the threaded hole, it's livable. Make sure the plate isn't warped tho. if so flatten it. you can check it for a flat plane on a piece of glass with a "very" thin film of grease on the glass. lay it on the surface and press in the center of the plate, lift it straight up and see if the grease is missing on any part of the plate. if so lapp it some more. Keep it simple, yu don't need a machine shop or a store for everything. Fear is the only thing that stands in the way of advancement.
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Old 07-11-2015, 12:21   #17
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Re: Raw Water Pump Woes

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good evening!

I'm broke down at Indiantown, Florida. Fortunately, I've got a spot on a dock - all is safe!

Catalina 320, 2001 Yanmar 3GM30 engine. Johnson F4B-903 water pump.

It's NOT pumping water. I'm generally pretty good at troubleshooting, but I'm stuck. Here's what I've tried doing/checking so far:

1. raw water thru hull is open!
2. raw water strainer is clear.
3. when I remove the raw water hose from the pump, it freely flows from the static pressure outside the hull (so I know the pump is getting plenty of water flow to it).
4. when I pull off the hose from the heat exchanger (just downstream of the pump), there is virtually no flow (just a trickle, if that)- with the engine running. in the past when I've been working on things, I get a strong hose-like stream here.
5. I pulled the pump off and apart.
6. Nearly new impeller. All the vanes are in good shape. this is the new style impeller that as a screw straight through the center/core, so I'm pretty sure it's not a spun hub.
7. the "plate" on the pump is a little worn/scored, but I've seen a lot worse still working great.
8. Nearly new o-ring on the plate seal.
9. I'm seeing no leaks at all when the pump is sitting still, or when running.
10. I am missing 1 of the 6 screws that hold the plate on. It's been working fine like that for years - no problem.

I am about ready to just replace the whole blankety blank pump with a new one, but a) they're expensive, and b) I will lose 4 days waiting for the part to arrive.

Any thoughts? Anything else I can try? I would really really like to solve this problem and push off.

thx, markb
Is the pump belt adjusted correctly? Have you got a water strainer before the pump? If not there may be something sucked in and blocking a hose upstream of the pump. Take off all the hoses one at a time to check for blockage. In an earlier motor without a strainer, I had a single fish scale blocking near the thermostat.
Check your thermostat/s. You can put it in a pot of water and heat it to see if it opens correctly.
I have also had wear in the back plate of the pump. A couple of times over the years I have spent an hour lapping the bronze plate on a sheet of glass with 280 wet / dry paper and lots of water. That does improve the flow. No need to replace the pump if you do that. Double check your impeller.


A boat moored near mine was having a cooling water problem with an air lock in a hose preventing flow. That's not likely if it's previously been OK but it's a possibility.
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Old 07-11-2015, 12:25   #18
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Re: Raw Water Pump Woes

I had a raw water pump impeller that looked perfect but was spun on its shaft and did not turn. It was near impossible to spot but in desperation I turned the shaft and discovered the sheared connection. A new impeller is inexpensive; good luck. foufou
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Old 07-11-2015, 12:51   #19
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Re: Raw Water Pump Woes

This weekend, I had the same symptoms on my port Volvo 1-30 with a similar pump. I went through the same trouble shooting process.; strainer clear, hoses looked good, front plate with a little wear, but looking good, all the vanes on the impeller, no cracks in the impeller, cross bolt intact, nevertheless, very little water was getting through.

Even though the impeller looked fine, I replaced it and the gasket. Surprise, surprise, upon re-assembly and engine start, the water is pumping fine. Maybe the old impeller was soft, (doubt it). Maybe the sides were too worn, I don't know, but a fresh impeller did the trick.
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Old 07-11-2015, 14:26   #20
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Re: Raw Water Pump Woes

Mr. Dochip...What a great guy for even making the offer to help a fellow cruiser out of a jam, I'll buy ya a beer David next time we're in the neighborhood ! Cheers
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Old 07-11-2015, 14:36   #21
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Re: Raw Water Pump Woes

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Originally Posted by tinkrman69 View Post
the above is a good start. altho I wouldn't use sealant, do put silicone grease on the O ring tho......

*Keep it simple, yu don't need a machine shop or a store for everything. Fear is the only thing that stands in the way of advancement.
Just to be clear, the concept of removing the O ring and using some very thin sealant is purely for trouble shooting. It is possible that for whatever reason, the O ring hasn't fully compressed thus leaving a small gap between impeller and cover.

You will note that I recommended refitting the O ring after this procedure

I fully concur with your last para
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Old 07-11-2015, 14:37   #22
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Re: Raw Water Pump Woes

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Mr. Dochip...What a great guy for even making the offer to help a fellow cruiser out of a jam, I'll buy ya a beer David next time we're in the neighborhood ! Cheers
Yes, +1K
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Old 07-11-2015, 17:34   #23
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Re: Raw Water Pump Woes

The exhaust elbow on the GM series used to last about 700 hours. Try removing the hose from the heat exchanger to the elbow. Suck a bit on the hose to draw prime. Crank w compression relief open for 15 seconds and see if any water comes out. If so, you might replace the elbow. /Stu
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Old 07-11-2015, 18:08   #24
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Re: Raw Water Pump Woes

I looked carefully at the plate and decided it was actually pretty badly scored. the grooves worn were probably 1 mm or more deeper. So i did what was suggested. I took the cover plate and sanded the paint off and smoothed the roughness on the FRONT side.

Put it back together and it pumps great.

I realize this may be a temporary solution, but gets me out if a jam. I will still get a replacement pump and keep this as a spare.

Thanks for your help .
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Old 07-11-2015, 18:13   #25
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Re: Raw Water Pump Woes

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I had the same engine in my previous boat and a similar raw water pumping problem. Check the hoses ... my issue turned out to be collapsed interior of hose. Also, in the event you need replacement parts Mattos Marine in Fort Myers, less than an hour by car, might have what you need in stock so you wouldn't have to wait. Their number is 239-332-2515. Uber might help if you have to go there, but in a pinch I might be able to pick up the parts there and drive them out to you.
Wow, thanks for the offer. the boating community is awesome. Fortunately we've got it solved. THANKS again.

Markb
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Old 07-11-2015, 18:49   #26
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Re: Raw Water Pump Woes

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Originally Posted by bratzcpa View Post
I looked carefully at the plate and decided it was actually pretty badly scored. the grooves worn were probably 1 mm or more deeper. So i did what was suggested. I took the cover plate and sanded the paint off and smoothed the roughness on the FRONT side.

Put it back together and it pumps great.

I realize this may be a temporary solution, but gets me out if a jam. I will still get a replacement pump and keep this as a spare.

Thanks for your help .
Excellent news!

Maybe temporary for quite awhile
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Old 07-11-2015, 20:02   #27
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Re: Raw Water Pump Woes

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Excellent news!

Maybe temporary for quite awhile

I am on year 2 of that very repair and there is no end in sight.
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Old 07-11-2015, 20:29   #28
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Re: Raw Water Pump Woes

If you pulled the outlet hose, that goes to the exhaust mixing elbow, you've got a heat ex changer blockage. Try back flushing the cooler, with the hose disconnected from the pump and see if that will do it. Use Salt Away for best results. If not available, soak with ordinary vinegar.
If not, pull the exchanger end off and get a piece of brazing rod to poke thru the tubes.
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Old 07-11-2015, 23:39   #29
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Re: Raw Water Pump Woes

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If you pulled the outlet hose, that goes to the exhaust mixing elbow, you've got a heat ex changer blockage. Try back flushing the cooler, with the hose disconnected from the pump and see if that will do it. Use Salt Away for best results. If not available, soak with ordinary vinegar.
If not, pull the exchanger end off and get a piece of brazing rod to poke thru the tubes.
Refer post #24...

Focus, you gotta stay with the program
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Old 08-11-2015, 12:55   #30
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Re: Raw Water Pump Woes

Just wondering if your problem could lie elsewhere. Despite new pump & impeller, I wasn't getting any water through my Yanmar. Problem very eventually identified as blocked-solid refrigeration heat exchanger through which the incoming water passed before going through the engine and blocked raw water exhaust elbow. Seems to me that water pumps on small Yanmars could do with being a bit gruntier, if there's such a word. A couple of years previously I found that a replacement Jabsco impeller which was said by the dealer to be correct for my motor, wasn't exactly the same dimension as the original Yanmar product for European made engines, hence the screeching and awful performance.
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