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Old 12-03-2018, 01:41   #1
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Generator overheat

I don't believe this problem is specific to Leopard because I have experienced it on Lagoons as well. Generator mounted on bridge deck, engine mounted flexible impeller pump can't handle the suction height so an electric pump is fitted to boost inlet pressure. Get about 500-1000 hours on the generator and it all ends in tears with pump losing prime after 20 minutes or so. My educated guess is that the system was set up for ideal conditions ex factory but with a tiny bit of wear it can't perform any longer. Surely I'm not the only one with this issue. Is there a reliable fix?
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Old 12-03-2018, 02:17   #2
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Re: Generator overheat

i fitted a12lpm 12v bait well pump and removed the impellor assembly works great on my mono comes on when genset starter engaged.

alternativly a 240v centrifugal pump in one of the hulls below the waterline would work with the genset impellor removed that comes on with the 240v output,i have this system for cooling the fridge condenser with circulation through one of the fresh water tanks,works great though a salt water spec pump would be needed to prevent corrosion for a genset using salt water cooling
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Old 12-03-2018, 02:36   #3
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Re: Generator overheat

Hmmm, hadn't thought of actually taking the engine mounted pump away entirely. What sort of lift are you looking at? The current pump in the boat we are trying to sort out is a 12.5 lpm at 1.2 metre head feeding a 7kw Northern Lights.
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Old 12-03-2018, 03:29   #4
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Re: Generator overheat

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Originally Posted by NoTies View Post
Hmmm, hadn't thought of actually taking the engine mounted pump away entirely. What sort of lift are you looking at? The current pump in the boat we are trying to sort out is a 12.5 lpm at 1.2 metre head feeding a 7kw Northern Lights.
i think the lift is about 4ft on the 12lpm pump,which is plenty for my 8kw genset ,but it is only 2ft away from the pump and only about 18inches above the waterline at the exhaust manifold.

a 15lpm pump probably would be more suitable with the pump mounted close to the waterline to act as a pump pushing water uphill rather than near the genset and using suction.

as these pumps are for continuos duty with no pressure switch, having the impellor in place might act as a restriction .
the same would apply to a 240v centrifugal pump.

care is also needed if the genset does not start immediatly with the 12v pump energised when ignition key is turned on to prevent flooding of the engine via the exhaust if it does not start immediatly.
with a 240v pump this would not be an issue as it would only run once the genset produces current.

the amount of cooling water will not matter if there is a slightly larger flow than with the impellor,as the closed freshwater loop /thermostat will control engine temp
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Old 13-03-2018, 12:49   #5
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Re: Generator overheat

We have an 11 KVA onan generator. The lift pump in the bilge is a 12V Jabsco cyclone continuous duty metal impeller - supposedly good for 3500 hours. We have 2500 hours on the genny and no problem with the lift pump. Two years ago we removed the rubber impeller from the engine raw water pump, the Jabsco has sufficient pressure so that the rubber impeller is not needed. The Onan has a raw water pressure sensor which does not trip in this configuration either. Also there is an in line check valve that stops back flow of water back past the lift pump. If that check valve leaks it will allow water to flow back out and the pump will lose prime.
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Old 14-03-2018, 00:23   #6
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Re: Generator overheat

Thanks for the replies, I sense a trend here. It looks to me like I will probably go with 230V pump for protection against flooding the engine but also because the AC pumps are a suitable size so a spare can be carried to fit all.
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Old 14-03-2018, 20:41   #7
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Re: Generator overheat

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Originally Posted by NoTies View Post
Thanks for the replies, I sense a trend here. It looks to me like I will probably go with 230V pump for protection against flooding the engine but also because the AC pumps are a suitable size so a spare can be carried to fit all.
Fair enough. I am overly cautious on wiring AC around a boat (or a house), so am happy for the 12 V system that is wired to the generator ignition.
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Old 15-03-2018, 00:15   #8
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Re: Generator overheat

Yeah, I'm comfortable with higher voltage, I like electricity you can feel. The biggest thing is not to have it energise on shore power or inverter which is easy enough to prevent.
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Old 15-03-2018, 00:38   #9
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Re: Generator overheat

On my cat i only have 1 yanmar mounted mid ships about a metre (3 ft) from the water. the inlet has a non return in it and the hose does a big loop around engine before it is connected to impeller pump. This loop helps the pump by giving it a gutfull of water on start up. The first time i changed the impeller i got rid of the excess hose around engine, then had continual priming problems, put the extra hose back and never had another problem even after being onthe hard stand, this might work for you.
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Old 15-03-2018, 00:41   #10
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Re: Generator overheat

The loop is around the base of the engine
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Old 15-03-2018, 03:04   #11
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Re: Generator overheat

It would be interesting to know how many hours you have. My experience has been that the problems start at around 500+. I have solved it on 2 other cats by fitting new pumps but this is not an ideal remedy at these hours. Bridge deck cat manufacturers need to start owning this problem. Whatever I do needs to be a long term fix and idiot proof. The vessel owner, whilst an interesting guy, uses litigation like I use oxygen.
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