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Old 01-12-2008, 09:06   #1
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How Much Is a Raw Water Pump Affected by a Scored Cover Plate ?

I have a 1982 Yanmar 2GM (raw water cooled).
The water pump works well enough to keep it running cool, for hours at a time.
However, I do have to close the raw water seacock, while sailing, or else (I assume) the suction of water past the boat's hull causes a pull on the water inside the thru-hull / hoses (maybe there is a small airleak that lets the water be pulled out more easily than normal????
In any case, as long as I close the thru-hull while sailing it's fine. If I forget to do that, I have to close it briefly with the engine running (to create more suction), or pull of a water hose, to get the water restarted.

The impeller has been changed, and both old/ new where in perfect shape.
I noticed a fair bit of scoring on the cover, and am thinking of replacing the cover with a speedseal cover, to see if it then pumps stronger, and may overcome the other issues.


If I could get a reasonably priced replacement pump, I would consider that as well, and keep the old one for a spare.

Thoughts??
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Old 01-12-2008, 09:11   #2
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I have not seen a water pump in use that does not have scoring marks inside the cover. You most likely have other issues and if you have a anti-siphon valve in the water line I would start there. Also look at the location of your raw water intake valve and see if it comes out of the water when healed over. If it does you will need to move it lower in the boat.
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Old 01-12-2008, 09:45   #3
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Chuck - Thanks again!

The seacock is very low, underneath the hull, so it does not come out of the water.
There is no anti-siphon on the raw water hoses, as I close it when off the boat.

I agree that there could be another problem, but it only happens when i forget to close the seacock while sailing. It can be open at the dock for a couple of days, and the water pump works fine, when I start the engine again.

I may be off base, but the raw water side, of a fresh water engine, will continually pump a high volume of raw water through the heat exchanger.

But, on my raw water cooled engine, it seems to pump much more water through, and out the exhaust, once the engine is warm, and the thermostat is opening regularly. I did take the thermostat out (replaced it just in case), and while looking at it, noticed that the hole where raw water bypasses to the exhaust, when the thermostat is not open, is very small compared to the size of the main thermostat opening!!

Therefore it makes sense, to me at least, that starting a cold engine, when the thermostat is closed for the 1st few minutes, would not allow the pump to push much water through to the exhaust, as the bypass hole is very small. That may cause the pump to have less suction, as it has nowhere to send the water to, and may cause me with the problem mentioned.

Open to input and enlightenment!!!
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Old 01-12-2008, 10:31   #4
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If you have had a raw water pump since 1982 then you have done a lot better than most. Its probably time to change out the raw water pump. Air could be getting in from from the bearing seal of the pump or from the gasket that seals the impellers cover plate. Pressure test your raw water intake hoses and your sea strainer for leaks by disconnecting your raw water hose at your pump and putting a little pressure in there from a garden hose with rags packed around it, with your seacock closed of course. Make sure your clamps are tight and the cap on your sea strainer is down tight. Does any water trickle out anywhere?

Also, you shouldn't have an air check valve in the suction side of your raw water system. All that's going to do is allow air in which is exactly what you don't want.
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Old 01-12-2008, 10:49   #5
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David- Sorry I was unclear. There is NO airbleed in the water hoses! What I meant was that a bit of air could be entering the system, through a bad connection, etc. You have addressed this concern by suggesting to pressureize it a bit, to see if it leaks. I can do that. It does not normlly leak any water from any hose, etc. The strainer is a brand new Perko last year, and seams to seal very well. The strainer and hoses are below waterline, as well.

You are right - it has worked since 1982, an I am lucky. However, I hate to replace a pump, for I assume several hundred bucks, when it worked great all summer (except the few times when I forgot to close, or purposely left the seacock open while sailing). Even then, as soon as I closed the seacock for a few seconds, or pulled a hose off and revved the engine a bit, it worked again well enough to keep the engine cool for hours of motoring.


I am thinking though, that because of possbile worn bearing seals, cover plate, etc. that it is likely not working at 100%, and therefore may not be strong enough to overcome the pressure / airlock issuse I get while sailing with the seacock open.
(By the way, although I don't think it is very common, there are others who have experienced the same airlock issue while sailing - there was a thread on it last year, but it didn't shed much light on it)

I will likely price a new pump. I would easily pay $100 for a new one, but I have a feeling it's going to be much more with Yanmar!!

Thanks for taking the time to reply and help!!!
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Old 01-12-2008, 12:49   #6
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I have had similar symptoms with a Johnson pump on a raw water cooled BMW d-35. In my case it was due to excessive wear on the cover plate. Many pumps covers are symmetrical,and can be turned over and replaced -- thus giving a new and unworn surface to seal against the end of the impeller. Of course, you need to clean the new surface up first!

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Old 01-12-2008, 12:56   #7
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Speed Seal?

When you are operating your engine, the inertia of the water flow off your pump impellor is sufficient to overcome the pressure in the exhaust manifold and inject the raw water stream into the exhaust mixing nozzle and thence into the water lift muffler--which is pressurized by the exhaust--and finally off-board.

If your raw water strainer is below the level of your water pump; and, if your pump cover is badly scored, or the sides of the impellor blades worn, when you shut down your engine with the through hull open, the residual pressure in your water lift muffler bleeds back to your pump, past the impellor blades if they or their cover is worn and into the intake line from the raw water strainer. This, plus the fact that by being below the pump, the strainer does not trap water in the hose between the strainer and the pump, will cause the hose to drain down at least to the level of the water line and, potentially more-so, if you happen to have a cover over the outside of the raw water through-hull to prevent debris from being pulled in. (Depending upon its shape, the "bump" of a strainer cover at the intake can cause a low-pressure zone at the through hull that sucks the water out of the intake line, in the same fashion that self-bailers suck water our of the bottom of a sailing dinghy.)

It may be that the least costly "partial" fix is to simply replace the cover on your pump with a Speed Seal (see Speed Seal EM4 Speed Seal for Yanmar Fresh Water Cooled Models: 3HMF, 3HM35F, 2 and 3 GMF Series and the Westerbeke 30B Three Ships Store Torresen ). However, while this will take care of the outside face of the pump, it does not address the inner face which may also be scored or badly worn due to sand or sediment having been drawn into the cooling system at some point. Unfortunately, there is no remedy for that although a good coating of pump grease on the inner face, coupled with a Speed Seal or new cover on the outer face may improve the situation--as will moving the raw water strainer to a position level with the pump if it is not already.

FWIW...

s/v HyLyte
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Old 01-12-2008, 13:14   #8
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HyLyte - thanks for the detailed response.

I hadn't thought about the possible backpressure the exhaust. I do NOT have a waterlift muffler. Just have a rubber silencer / muffler, that is nothing more than a small rubber bladder that the exhaust ad water goes through before going to a high loop, then out a thru-hull. I doubt whether this would hold / pass bac kas much pressure towards the pump as a waterlift would.

From taking out the impeller, and looking at the back or the pump, it does not appear to be scored as badly as the front cover, and that is why I was considering the speed-seal as a way to buy a new cover, and upgrade for easier maintenance / rubber o-ring (instead of paper gasket) at the same time.

re: the strainer, the bottom is about even height with pump, and the inlet and outlet hoses are at the top, approx 5" above the pump, but also below waterline.


Jim - I have heard about flipping the cover over, to get the new surface. However I ran this by my auto mechanic brother last year, and he didn't think it would work well on mine. I believe he thought the shape was a bit different, or had some other reason, although it looks the same to me!
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Old 01-12-2008, 15:01   #9
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May be looking in the wrong place !

At the top of the exhaust riser ther is a hose and a 90 degree elbow which allows water into the exhaust system. These should be completely dismantled as they are notorious for blocking with stuff like bits of water impeller,twigs, growing critters and other stuff that somehow makes it past your strainer basket.
On start up at idle speed -not max throttle- there should be a little time before you see water at exhaust as exhaust pressure in the water lift is needed to expell water.
A full removal and inspection of all hoses would also be recomended

A badly worn plate will reduce performance creating too much gap. On the 2 gm you can remove the cover, clean off the paint from the outside and put it on backwards.

Checklist-
strainer over intake- many are put on backwards ! unlike the cover plates these should not be.
Sea cock- Should be a proper ball valve with full dia. opening- not household plumbing gate valves.
Removing or replacing hoses- much better seal when hose end is warmed in hot water- and not overtightened- snug is good- overtightening distorts the hose and allows gaps.
Strainer basket seals - clean and seal.
Regards
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Old 01-12-2008, 15:47   #10
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Over..-

At the top of the exhaust riser ther is a hose and a 90 degree elbow which allows water into the exhaust system. These should be completely dismantled as they are notorious for blocking with stuff like bits of water impeller,twigs, growing critters and other stuff that somehow makes it past your strainer basket.

- I DID TAKE OFF THE EXHAUST ELBOW LAST YEAR, AND EVEN THOUGH IT LOOKED CLEAN AND I OCULD BLOW AIR EASILY THROUGH THE WATER HOLE I SOAKED IT IN MURIATIC ACID TO MAKE SURE. AS MENTIONED, NORMALLY WORKS FINE .. LOTS OF WATER FLOW.

On start up at idle speed -not max throttle- there should be a little time before you see water at exhaust as exhaust pressure in the water lift is needed to expell water.

- I DON'T DISAGREE - HOWEVER, HAVING SEEN THE SMALL SIZE OF THE BYPASS HOLE ON THE THERMOSTAT, I THINK IT REASONABLE TO NOT GET MUCH WATER UNTIL THE THERMOSTAT OPENS. I DON'T HAVE A WATERLIFT, JUST A RUBBER SILINCER /MUFFER.



A full removal and inspection of all hoses would also be recomended


- i HAVE REMOVED / INSPECTED ALL HOSES PREVIOUSLY. I CAN EASILY BLOW AIR / WATER THROUGH ALL HOSES AND THE BLOCK


A badly worn plate will reduce performance creating too much gap. On the 2 gm you can remove the cover, clean off the paint from the outside and put it on backwards.

- i WILL TRY CLEANING UP THE OTHER SIDE, AND SEEING IF IT WORKS BETTER. I MAY USED A DRILL TO SPIN THE PUMP (OFF THE BOAT) TO SEE HOW MUCH IT PUMPS NOW. THEN CHANGE THE COER PLATE AND TRY IT AGAIN, AT A FIXED RPM ON THE DRILL

Checklist-
strainer over intake- many are put on backwards ! unlike the cover plates these should not be.
- CHECK

Sea cock- Should be a proper ball valve with full dia. opening- not household plumbing gate valves.
- CHECK
Removing or replacing hoses- much better seal when hose end is warmed in hot water- and not overtightened- snug is good- overtightening distorts the hose and allows gaps.
- CHECK
Strainer basket seals - clean and seal.
- CHECK
Regards

THANKS FOR TAKING THE TIME TO RESPOND , WITH LOTS OF INFORMATION!!!
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Old 01-12-2008, 22:51   #11
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I have a raw water cooled 1gm10 and interestingly enough I was having discussion about the amount of water out the exhaust with a mechanic. He stated quite clearly "always check the cover on the impeller for scoring as is reduces the suction of the pump". I would go pick one up next impeller change.
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Old 02-12-2008, 06:22   #12
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Take a look to see if you can flip the impeller cover over so that the smooth side is facing inward. That would let you see right away if it's the scoring that's the problem.
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Old 02-12-2008, 07:10   #13
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After pondering this for awhile it occured to me that your "rubber bladder" in lieu of a water lift muffler may be internally fitted with a duck-bill valve, similar to the joker valve in a head to prevent back flow and maintain the prime in your raw water system. If this is worn or damaged from age, the back flow through while sailing as previously discussed, coupled with a weaked suction in the pump from wear, could be the source of your difficulties.

FWIW...

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Old 02-12-2008, 08:12   #14
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In general, when it comes to pumps and pump questions, Depco is your friend. Give 'em call!

DISCLAIMER: I have no connection with Depco save as a customer.
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Old 02-12-2008, 19:15   #15
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One would think so, but this is from experience. It is amazing what gets by the thermostat.
I had a couple of pieces of impeller, a very thin flexible stick about 3 inches long, and a bit of other ?????stuff. Plugged her up so that anything above an idlle would cause an overheat.
It will only take you a couple of minutes at no cost to check
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