water pump impeller issues, answers needed

Scillypete

Scillypete

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www.peteandspamgosailing.blogspot.com
The engine is a Yanmar 3YM30 2004 vintage and its fitted in a prout quest 33cs, we had poor water flow problems on the delivery trip after buying the boat last May but a change of impeller seemed to fix that the one that came out had a split in one of the fins. That new impeller worked fine until this summer when I had no flow at all so changed for a new one which seemed to do the job, the one I took out looked to be in good condition with no apparent damage at all, that was three weeks ago. This Sunday the same problem again no water being drawn through on start up even with plenty of revs so shut down again and pulled the impeller, nothing appears to be wrong with it at all but put another new one in and hey presto we have water again. I'm beginning to wonder if it is an impeller problem or whether something has gotten into the pipework and is causing a blockage that moves after a while to let the water flow and if so how the hell would I find it?

I can't afford to be changing impellers at the present rate . . . . help
 
Not an engine I'm familiar with, but the problem is familiar. It may not be a single thing wrong, but several.

The pump may be worn - is the face plate scored at all? If so, water may leak around the vanes of the impeller - a new one may be just wide enough to get the pump to prime?

Is there a water filter fitted? Does the lid seal well? If not, losing the prime may be making it worse.

Is the intake clear? When did you last check?

Is the exhaust elbow clear? This is another place that a partial blockage may occur.

I suppose that you thinking that there's a blockage may suggest there is no filter, so I'd start with the possibility of the pump being worn. I wonder where the boat came from when you bought her - was it sandy or muddy there?
 
Not sure on the pump used on that engine off the top of my head, but, try turning the faceplate over. Your symptom would fit well with a worn faceplate. You only need a few thou of wear, to cause problems.

Jon
 
Depending on the impeller, it has been known for the bush inside the impeller centre to rotate, but with a broken bond between the impeller and the bush, for the impeller itself not to rotate, or to rotate more slowly. Look at one of the failed imps you've removed - can you rotate the vanes without the central metal bush moving?
 
Scillypete said:
The engine is a Yanmar 3YM30 2004 vintage and its fitted in a prout quest 33cs, we had poor water flow problems on the delivery trip after buying the boat last May but a change of impeller seemed to fix that the one that came out had a split in one of the fins. That new impeller worked fine until this summer when I had no flow at all so changed for a new one which seemed to do the job, the one I took out looked to be in good condition with no apparent damage at all, that was three weeks ago. This Sunday the same problem again no water being drawn through on start up even with plenty of revs so shut down again and pulled the impeller, nothing appears to be wrong with it at all but put another new one in and hey presto we have water again. I'm beginning to wonder if it is an impeller problem or whether something has gotten into the pipework and is causing a blockage that moves after a while to let the water flow and if so how the hell would I find it?

I can't afford to be changing impellers at the present rate . . . . help
Click to expand...

Same engine, mine has a Vetus water strainer above the engine, lightest air leak round big top seal can cause same problem. Silicone grease on big rubber O-ring on water strainer helps greatly.

Your 3YM30 must be a very early serial no engine. My early 3YM30 can sometimes be persuaded to overheat even with full water flow if run at 3000-3400 rpm for ten minutes plus. It has the upgraded heat exchanger as fitted to later engines, done under warranty by Yanmar, this reduced but has never quite eliminated the overheating issue.

On my engine the faceplate has been reversed as the inner side was worn. I've also had a new water pump fitted, as the engine has quite high hours. The local Yanmar engineer says the engines are excellent but the Johnson water pumps fitted are pretty x@$#.
 
Thanks for the replies so far, yes it is a Johnson pump, the vetus strainer seems a good tight fit and has been greased so I don't suspect an air leak there. The cover plate has got some minor scoring and is no doubt not helping, I shall try a new cover plate for that.

All the impellers seem to be fine when drawn out and have a pin through the centre so there is no separation there and I have checked for that.
 
Scillypete said:
Thanks for the replies so far, yes it is a Johnson pump, the vetus strainer seems a good tight fit and has been greased so I don't suspect an air leak there. The cover plate has got some minor scoring and is no doubt not helping, I shall try a new cover plate for that.

All the impellers seem to be fine when drawn out and have a pin through the centre so there is no separation there and I have checked for that.
Click to expand...

If replacing the cover, check whether Speedseal have a replacement. Much better than the standard flat plate and no fiddly screws to lose in the bilges.
 
Tranona said:
If replacing the cover, check whether Speedseal have a replacement. Much better than the standard flat plate and no fiddly screws to lose in the bilges.
Click to expand...

funny you should put that as that is exactly what I have just been investigating just need to confirm the exact model of pump and I'm there . . . . . . fingers crossed the problem will be solved by this easy step
 
Scillypete said:
funny you should put that as that is exactly what I have just been investigating just need to confirm the exact model of pump and I'm there . . . . . . fingers crossed the problem will be solved by this easy step
Click to expand...

If the pump is about 2 5/16" then Speedseal can't help.
However if the pump casing is about 2 3/4" you will be in luck.
 
Check there are no kinks in the hoses both to and from the pump. And make sure the inlet hose isn't weak collapsing under the vacuum.
 
i,m not sure about a Johnson pump but in a jabsco pump there is there is a faceplate and a back plate and if one is worn then it stands to reason the other one is and there is a cam this will also have signs of wear usually replacing any one of these will increase water flow but only for a short time, as indeed will the impellor as you have found.hope you have managed to sort it .but beware the only good job is to replace all four components. Kieron
 
I had this problem on my 3YM30 second season after installation. It appeared to be caused by corrosion of the Johnson pump cover plate the material of which seems to be poor quality. Removing the plate at the end of the season and giving it a polish then refitting at the start of the next season seems to fix the problem. Engine has now done 600 hours on the same impeller. If you take the cover off after a couple of weeks without use the pump body internals still look like new but you can see a corroded imprint of the impeller on the cover and signs of corrosion pitting. After the first winter with the cover in place it was in a terrible state. I have not had it analysed but it looks as if the cover is just plain brass whereas the body may well be bronze.
 
Just had my 3YM20 serviced. Without me asking the engineer warned that the Johnson water pumps fitted on the engines were made of an inferior brass, and that the chamber and cam slowly corrode, eventually preventing a prime. Only answer is to swap out the pump, he said. When does it happen? After about 10 years, apparently.
 
I've a 3YM20.
The problem of water-flow failure is one I've experienced.
A certain solution is to rebuild the pump with new bearing and water seal.
Parts costs (buy from Johnson) are negligible, the rebuild takes about 20'.
Possible reason cited is that the bearing wear, though unnoticeable, is sufficient to allow the impeller to "float" and not seal properly.
Last rebuild I had done (I always carry a spare raw-water pump) cost me €18.50, mainly for the parts, in Mytilini in Lesbos,
 
I had the same symptoms, it was air being drawn passed the seals on the shaft. New pump from ASAP. No further grief for past two years.
 
My water pump on 3GM30F would sometimes fail to prime after sailing in bouncy conditions. It did this for quite a few years until the shaft seal failed completely. Since replacing it the problem has never recurred, although from time to time I do re-face the front plate. I assume that air was being drawn through the poor original seal.

The Yanmar seals have brass or bronze springs that corrode and fail after a while. Volvo ones, identical dimensions, have stainless steel springs but, as ever, cost a packet. Marine Power stock reasonably-priced alternatives with stainless steel springs.
 
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