KAD42 keeps shredding impeller

Nick101 said:
Hi, I had the same problem a couple of years ago with a KAD43. In the end it turned out to be a small imperfection in
the pump. As soon as we changed the waterpump the problem was cured. Cost me four impellers though, regards Nick
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Am I missing something here/ I thought that the impeller is the pump. ie the bit that moves (Pumps) the water. If this is not the case what is the pump

Dennis
 
Bigplumbs said:
Am I missing something here/ I thought that the impeller is the pump. ie the bit that moves (Pumps) the water. If this is not the case what is the pump

Dennis
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The pump body is the brass bit around the impeller.
If the brass bit is worn (wrong shape), or the cover plate is worn (no seal with the impeller), then the whole thing doesn't self-fill with water.
Instead it pumps air, gets very hot, and the impeller changes into lots of very small bits of impeller. This is not good.
 
BruceK said:
... I have removed the hose downstream from the basket and a fair amount of water gushed out then stopped. (yes it scalded my hand trying to catch any wayward impeller bits that might have got past the basket...doh!) ...
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A clue in your opening post - the water scalded your hand. The seawater should at best get warm after the heat exchangers, and should be cold after the pump.

My money is on a blockage, and as VP says small bits of impeller in the oil cooler. I would try to back flush the cooler, and possibly remove the end caps to rod the tubes out, but check also the heat exchanger and after cooler isn't crudded up.
 
Solved. Air was leaking through the impeller shaft. The fact the water wasnt leaking out through the shaft hid the fact the seal was worn. It wasnt leaking badly but enough at high revs to create an airlock. Thanks VP for sugesting this in pm.
The heat exchangers do need rodding out this year as temps to get to the high 80s under load dropping to 80 the instant you come off the plane but Im going to try this Rhydlyme this year. Last year I had to replace an oilcooler after damaging the endcap trying to release it.
 
BruceK said:
Solved. Air was leaking through the impeller shaft. The fact the water wasnt leaking out through the shaft hid the fact the seal was worn. It wasnt leaking badly but enough at high revs to create an airlock. Thanks VP for sugesting this in pm.
The heat exchangers do need rodding out this year as temps to get to the high 80s under load dropping to 80 the instant you come off the plane but Im going to try this Rhydlyme this year. Last year I had to replace an oilcooler after damaging the endcap trying to release it.
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Rydlyme is excellent, I now tend to use it undiluted, even better if you can keep,it moving by having a system that recirculates it constantly. Unfortunately won't get rid of bits of rubber impeller........
 
BruceK said:
Solved. Air was leaking through the impeller shaft. The fact the water wasnt leaking out through the shaft hid the fact the seal was worn. It wasnt leaking badly but enough at high revs to create an airlock. Thanks VP for sugesting this in pm.
The heat exchangers do need rodding out this year as temps to get to the high 80s under load dropping to 80 the instant you come off the plane but Im going to try this Rhydlyme this year. Last year I had to replace an oilcooler after damaging the endcap trying to release it.
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Well done Bruce now you can get on with your season

Dennis
 
longjohnsilver said:
Rydlyme is excellent, I now tend to use it undiluted, even better if you can keep,it moving by having a system that recirculates it constantly. Unfortunately won't get rid of bits of rubber impeller........
Click to expand...

I have painstakingly rebuilt the shredded impeller with superglue. I'd like to say I have every single last piece but I'd be lying. However those pieces that are missing are significantly less than 6mm and will transit the coolers..... I hope? I removed the pipe to the oil cooler and stuck a finger in, it wasn't very successful in terms of feel about but the system has been backflushed when the hose came off.

How exactly does one take the end caps off an oil cooler intake side without ruining it?
 
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Sorry Bruce but trying to recall what your oil cooler is like? if it is of the bowman type then just undo the three bolts holding the end plates on and the thing should fall off, if not then a tap around the edges should move it. The oils is in the main can and the raw water goes through the reeds. The only thing that can be holding the ends is corrosion. I am not trying to be facetious. On a Sabre or Mermaid the raw water transits as follows, water inlet, strainer, jabsco pump, intercooler, gearbox oil cooler, engine oil cooler, header tank, exhaust elbow and out with exhaust. So we start at the pump/intercooler joint, and find nearly all the bits there. Anything that gets beyond there will go straight out the back. (fingers crossed.)
 
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Hi

Tapping round the edges of the last one did nothing but deform it. I appreciate it may have corroded on a bit but it was an expensive error. I bought some extra clear reinforced hose and back flushed it under some pressure. Flow was very good and if anything is in (doubtful) it isn't coming out. Gave the boat a good run of 20 nm under max revs and temps were as above which was what she was before the impeller break up and as per last season. I'm loathe to dig deeper. The problem with older boats is you are guaranteed to find a problem if you look hard enough for it.
 
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