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Old 02-07-2022, 17:31   #1
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Raw water pump

Help please- 3TNV-70H Yanmar on Mase generator. I have recently replaced Johnson impeller but now have a water flow issue. On start -up ,the raw water flow is very slow to nil. Stop and re-start and the flow is normal. Have tried priming ,all connections ,cleaning heat exchanger. I have read previous blogs but still can't locate problem . Any advice please ?
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Old 02-07-2022, 18:28   #2
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Re: Raw water pump

So the flow is now normal or do you have nil flow every time you initially start and only have flow after restarting each time?
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Old 02-07-2022, 20:42   #3
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Re: Raw water pump

G'day , The flow has been nil every start since changing the impeller. If I stop engine , after about a minute , then re- start , then the flow is normal , 100 %. At next start , say next day , again nil until a re-start.
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Old 02-07-2022, 22:24   #4
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Re: Raw water pump

Sounds like a blockage between the pump and the intake through hull. I would also open the pump again and check it because if that is the only change you made then it is most likely the culprit.
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Old 02-07-2022, 23:02   #5
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Re: Raw water pump

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Originally Posted by BobFord View Post
Help please- 3TNV-70H Yanmar on Mase generator. I have recently replaced Johnson impeller but now have a water flow issue. On start -up ,the raw water flow is very slow to nil. Stop and re-start and the flow is normal. Have tried priming ,all connections ,cleaning heat exchanger. I have read previous blogs but still can't locate problem . Any advice please ?
Hi, when you changed the impeller did you replace the wear plate ot the rear and faceplate, or at least lapped them to ensure a smooth face that will not allow air to enter the system, causing the symptoms you report?
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Old 02-07-2022, 23:39   #6
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Re: Raw water pump

^^^^^

Or possibly use a thicker gasket than required or perhaps put the new gasket on top of the old one?

End clearance on the impeller is critical... as Bob mentions above, leakage there can cause the very symptoms you are suffering,

Jim
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Old 03-07-2022, 00:24   #7
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Re: Raw water pump

Many thanks for your suggestions ,good crew ! I will start with 'rodding' the r/w inlet riser. Then dismantle and check issues mentioned re pump. Hey Jim Cate -we are planning a summer in Tassie, departing BNE December. However ,here in GKI it is very cold !! The last of Winter ,we hope !
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Old 03-07-2022, 14:36   #8
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Re: Raw water pump

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Many thanks for your suggestions ,good crew ! I will start with 'rodding' the r/w inlet riser. Then dismantle and check issues mentioned re pump. Hey Jim Cate -we are planning a summer in Tassie, departing BNE December. However ,here in GKI it is very cold !! The last of Winter ,we hope !
Cold at GKI? surely you jest!!

Currently we're having 2-5 degrees at night, max of 10-13 in the daytime, as measured by the wx station at the Port Cygnet Sailing Club (data available at

https://www.weatherlink.com/bulletin...9-f7196b23ffd9

if you should be interested.

When you get down here, make yourself known.

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Old 03-07-2022, 15:11   #9
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Re: Raw water pump

Best thing we ever did was get rid of the impeller pump and wire in an MD30 electric pump

5 years zero issues zero impeller changes as it hasn't got one as such
No more swearing and blood letting

https://www.ebay.com.au/itm/192171057207
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Old 03-07-2022, 15:58   #10
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Re: Raw water pump

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Originally Posted by Simi 60 View Post
Best thing we ever did was get rid of the impeller pump and wire in an MD30 electric pump

5 years zero issues zero impeller changes as it hasn't got one as such
No more swearing and blood letting

https://www.ebay.com.au/itm/192171057207
Well it obviously works for you but I see 2 issues. One if your engine doesn't start immediately you risk flooding the exhaust system. and the second is the water throughput is no longer relative to engine rpm as most cooling systems are designed for ! Those pumps are designed for HVAC units. Oh forgot the fact you need your inverter on all the time.
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Old 04-07-2022, 07:18   #11
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Re: Raw water pump

Emmalina,
you must have missed to read the "Mase generator" part.
On a generator the electric pump makes perfect sense.
It's wired directly to the power outlet of the genny. Engine not running, no power, no water flow. The genny runs on fixed RPM thus no need to vary the flow.
The only "issue" I can come up with is that those electric pumps are not self priming which then could lead to cause other problems.
Other than that, no more impeller changes sounds very attractive to me.
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Old 05-07-2022, 13:47   #12
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Re: Raw water pump

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Emmalina,
you must have missed to read the "Mase generator" part.
On a generator the electric pump makes perfect sense.
It's wired directly to the power outlet of the genny. Engine not running, no power, no water flow. The genny runs on fixed RPM thus no need to vary the flow.
The only "issue" I can come up with is that those electric pumps are not self priming which then could lead to cause other problems.
Other than that, no more impeller changes sounds very attractive to me.
Yep forgot about the genset comment. Those pumps are all centrifugal so won't self prime. As long as they are below the waterline should be ok. I have mounted centrifugal pumps on engines with a spare pulley before now but had to fit a gate valve to limit flow.
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Old 05-07-2022, 22:06   #13
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Re: Raw water pump

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Originally Posted by Emmalina View Post
Well it obviously works for you but I see 2 issues. One if your engine doesn't start immediately you risk flooding the exhaust system. and the second is the water throughput is no longer relative to engine rpm as most cooling systems are designed for ! Those pumps are designed for HVAC units. Oh forgot the fact you need your inverter on all the time.
One of the ways around this is to wire the pump motor through a relay. Wire the pump through the normally closed contacts and the actuator through the oil warning switch. When you switch the ignition on the normally closed relay will try to turn the pump on however the oil warning going on will pull the relay to off. When the oil light goes off the relay will de-energize allowing the normally closed contacts to switch the pump on.
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