Impeller Longevity

[Dockhead]

Originally Posted by poiu

Impressive that you didn't destroy it. Maybe you are able to suck water in another route, backward through an outlet in your engine or genset that isn't into an exhaust cooler maybe?

I normally go for 2 years and 200 hrs and I find a small crack. I destroyed one from overuse at 3 years and maybe 300 hrs. That's clearly too long. It was a slow overheat with no great drama.

I think the life depends also on shelf age too as the environment, ozone for example, damages the material.

Remind me please, what kind of engine do you have in that boat? Is it the six cylinder Perkins?

[sailorboy1]

Originally Posted by Dockhead

Yes, and after 7 years and almost 2000 hours of experience, I can say that at least on my installation, 600 hours is realistic.

I checked mine the other months, it has 1300 hours and looks fine.

[steve77]

Originally Posted by Dockhead

I thought it was shot, as the boatyard here in Cowes lifted my boat in my absence for a scrub and anode change, and forgot to open the sea cocks. They ran it for about half an hour with the sea cocks closed.

Do I understand you to say that it is possible to run your Yanmar for a half hour with the sea cock closed and the high temp alarm doesn't go off? I understand that this was done by the boatyard, not by you. I would have thought that even a freshwater cooled engine would have gotten pretty hot after half an hour of running if seawater were not removing heat via the heat exchanger.

I have the same engine, and change the impeller every other year. I use the Globe impellers that advertise 15 minutes of running dry, and also have the speed seal kit with the teflon disk.

Cheers!

Steve

[Scott Berg]

Impellers are fairly cheap, even for my Lehman SP135. We replace every other year unless we show more than 300 hrs, then we replace at 300; yes, I suspect I toss out a perfectly good impeller; but we've never lost one in anger and I've delivered enough boats to know many people have. Our genset impeller is much harder to replace so that is done yearly so it NEVER fails. Much easier in a cool engine room with time to work easily.... to each ones own; but prior preventive (maintenance) prevents Pi.... as you know

[Pete7]

I would be tempted to inspect the inside of the exhaust hose because that has had a lot of heat and no water to cool it.

Peter

[athene]

Bit tangential, but I fitted a Halyard Sea Strainer alarm on the intake pipe of our motor boat and wouldn't now be without it. The Sea Strainer works on a vacuum principle, so alarms immediately if there is any blockage in the intake (as opposed to an exhaust alarm, which tells you that the impeller is already burnt out).

One picks up a lot of crud in the European inland waterways - invariably in the middle of a delicate manoeuvre such as leaving a lock - and it's saved our impeller and our sanity at least 15 times in the past two years.

This thread has reminded me that fitting one on our sailing boat as well has been too long on the jobs list...

GORDON KNIGHT

[Dockhead]

Originally Posted by Pete7

I would be tempted to inspect the inside of the exhaust hose because that has had a lot of heat and no water to cool it.

Peter

I did!

The engine was mostly idling, which is the only reason why it didn't melt down the exhaust. A diesel at idle is essentially air-cooled.

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[Suijin]

Originally Posted by Dockhead

I thought it was shot, as the boatyard here in Cowes lifted my boat in my absence for a scrub and anode change, and forgot to open the sea cocks. They ran it for about half an hour with the sea cocks closed.

An alternative theory. You weren't there. How do you know how long they ran it, if they even ran it at all? Many yards have skiffs rigged to move boats to the haulout without even a person on the boat other than to cast off lines.

Even if they told you they ran it, because the manager thinks they did, they may have not.

I have a hard time believing that any impeller, speedseal or no, would survive 30 minutes of running dry. Even at idle it's turning quickly enough to generate enough heat to self-destruct.

[Dockhead]

Originally Posted by Suijin

An alternative theory. You weren't there. How do you know how long they ran it, if they even ran it at all? Many yards have skiffs rigged to move boats to the haulout without even a person on the boat other than to cast off lines.

Even if they told you they ran it, because the manager thinks they did, they may have not.

I have a hard time believing that any impeller, speedseal or no, would survive 30 minutes of running dry. Even at idle it's turning quickly enough to generate enough heat to self-destruct.

There were signs - waterlift full of water, scuff marks on the Teflon, key was taken out.

Sent from my D6633 using Cruisers Sailing Forum mobile app

[fallingeggs]

Perhaps a flow alarm is in order!

Cooling Water Flow : AQUALARM, Warning Systems For Land And Sea

I'm installing this, along with their exhaust hose temperature sensor, this winter/spring.

The only thing that ever worries me about my engine (actually, about the whole boat) is it overheating. She did it to me once and now I'm scarred.

[poiu]

Originally Posted by Dockhead

Remind me please, what kind of engine do you have in that boat? Is it the six cylinder Perkins?

Correct. With a block mounted Jabsco sea water pump.

[btrayfors]

Over a lifetime of boating I've found it good practice to:

1. replace the impeller every year; and

2. glance over the side EVERY TIME YOU START THE ENGINE to verify good water flow.

Make these standard practice on your boat and you'll never have a problem.

NB: the cost of a new impeller is insignificant compared to the potential damage from a damaged impeller, a closed seacock, a clogged water intake strainer, etc., etc.

Bill

[kmacdonald]

My 2 and a half year old Kubota with Jabsco raw water pump has 720 hours on it and no sign of any problem. I'm just starting to think of replacing it. Maybe next year.

[Dockhead]

Originally Posted by kmacdonald

My 2 and a half year old Kubota with Jabsco raw water pump has 720 hours on it and no sign of any problem. I'm just starting to think of replacing it. Maybe next year.

You revived an old thread!


I do mine every other year, and it always look more or less like new when I take it out. I'm sure it could go longer but why risk it?



I wouldn't recommend letting it go until it fails -- the consequences are unpleasant. At 2 1/2 years and 720 hours I think I would replace it.

[rslifkin]

Originally Posted by Dockhead

You revived an old thread!


I do mine every other year, and it always look more or less like new when I take it out. I'm sure it could go longer but why risk it?



I wouldn't recommend letting it go until it fails -- the consequences are unpleasant. At 2 1/2 years and 720 hours I think I would replace it.

I'm on the same schedule. Every 2 years regardless of hours. And on my engines with the plastic Mercruiser pump housings, the housings and wear plate get changed as well.