Lost impeller blade in 3YM20

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tchierici

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The impeller on my Yanmar 3Ym20 broke and I have lost the blade. I checked in the pipe going out from the water pump and I suspect it travelled up into the engine. I read somewhere that it might have got stuck in the heat exchanger, which is only accessible by dismantling the alternator. Is there any other way to get the blade out? Can it be flushed out by reverse flushing?
 
tchierici said:
The impeller on my Yanmar 3Ym20 broke and I have lost the blade. I checked in the pipe going out from the water pump and I suspect it travelled up into the engine. I read somewhere that it might have got stuck in the heat exchanger, which is only accessible by dismantling the alternator. Is there any other way to get the blade out? Can it be flushed out by reverse flushing?
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Been there with the 30 version. You have to take the alternator off and then get to the heat exchanger.
 
I'm not familiar with your particular model of engine, but normally with indirect-cooled marine diesels it is a periodic winter servicing job to dismantle the heat exchanger to remove limescale etc. Normally it's also the only solution to locating all the bits of a failed impeller, so really I think you should bite the bullet and learn how to do it now. It can be more laborious on some engines tham others, but is on the whole a pretty simple and logical operation.
Edit:
Download a free Operator's Manual here:
Yanmar 3YM20 Manuals | ManualsLib

You can buy a workshop manual (priced €16.99) through this link:
Yanmar Marine Diesel Engine 3YM30, 3YM20, 2YM15 Service Repair Workshop Manual
 
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It is best to also push a rod or tube brush through all the heat exchanger tubes to remove any small pieces trapped. It is surprising ho the high velocity of water past an obstruction can cause erosion of the tubes. Might have to run a few ours but I have seen it happen.
 
I also have a 3YM30 and have, in the past, had to go find a lost impeller fin.

It will almost certainly be at the inlet to the heat exchanger and you will need to get the alternator out of the way. Either by removing it or by removing enough of the bolts and then swinging it out of the way. A socket set with an extension rod and long handled Allen keys make this job easier.

And once you’ve got the bits out then worthwhile putting the bits back together to check you’ve found them all.
 
If one impeller blade has gone awol and is small enough to get through the pipework into the heat exchanger then I personally would not bother dismantling the heat exchanger to find it. There are stories on this forum of people changing shreded impellers every year and finding lots and lots of bits when they take the heat exchanger apart. If your heat exchanger has not had a good clean out for years or you need to change the coolant / hoses then I would go for the refurbishment otherwise I would not bother for 1 piece. In these days of dodgy supply chains I would get a new set of heat exchanger o rings before starting the job as you will need to replace them. Remember to use approved coolant (OAT type)
 
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Halo said:
If one impeller blade has gone awol and is small enough to get through the pipework into the heat exchanger then I personally would not bother dismantling the heat exchanger to find it. There are stories on this forum of people changing shreded impellers every year and finding lots and lots of bits when they take the heat exchanger apart. If your heat exchanger has not had a good clean out for years or you need to change the coolant / hoses then I would go for the refurbishment otherwise I would not bother for 1 piece. In these days of dodgy supply chains I would get a new set of heat exchanger o rings before starting the job as you will need to replace them. Remember to use approved coolant (OAT type)
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The engine is practically new and only done 100 hours. Are you saying that leaving the broken blade in the exchanger is not a big deal for now? I suppose it shouldn't affect water flow anyway. To be honest the water flow was great even with the broken impeller, in fact I didn't even realise that it had broken until I opened the water pump while winterising engine.
 
tchierici said:
The engine is practically new and only done 100 hours. Are you saying that leaving the broken blade in the exchanger is not a big deal for now? I suppose it shouldn't affect water flow anyway. To be honest the water flow was great even with the broken impeller, in fact I didn't even realise that it had broken until I opened the water pump while winterising engine.
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Halo said:
If one impeller blade has gone awol and is small enough to get through the pipework into the heat exchanger then I personally would not bother dismantling the heat exchanger to find it. There are stories on this forum of people changing shreded impellers every year and finding lots and lots of bits when they take the heat exchanger apart. If your heat exchanger has not had a good clean out for years or you need to change the coolant / hoses then I would go for the refurbishment otherwise I would not bother for 1 piece. In these days of dodgy supply chains I would get a new set of heat exchanger o rings before starting the job as you will need to replace them. Remember to use approved coolant (OAT type)
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3 small pieces of impeller, plus limescale type gunk, made enough of a blockage in my heat exchanger end cap to cause overheating. Beta 20. I'm told that the Beta heat exchangers are precisely sized (= a little small) so even a small blockage can cause problems.
 
After only 100 hours service on a new engine I would say the heat exchanger should not be suffering from a gunk build up and if, as you say, the flow rate looks really good its hard to see the justification for a strip down . Even good mechanics can cause secondary problems stripping down and rebuilding engines. If the rubber blade is in small pieces then I suspect it could have gone through and out of the exhaust - how will you feel if you take it all apart and find nothing ? its your shout but I personally would either back flush or simply leave well alone in this case.
 
My advice would be to talk an hour and fish the broken bit out. It’s not a hard job - it’s almost certainly lodged in the inlet of the heat exchanger.
 
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