Impeller Longevity

[Dockhead]

I just replaced the impeller in my Yanmar main engine (4JH3HTE). It's been two years and 10,000 miles, and about 500 hours of motoring.

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.

But the impeller was immaculate, with nary a crack in it.

Could it be because the sea water pump is below the water line, which means that the sea water pump always has water in it? The impeller in my generator -- sea water pump well ABOVE the water line -- blows up in an ugly fashion within seconds, if I forget to open the sea cock (which happens more regularly than I would like to admit).

[bytownboy]

Change my impellor on my 4JH HTBE every 500 hours. Last summer it went at 476 hours, about a mile from the anchorage I was motoring to. Go figure. Tied dinghy to boat and had my 2.5 Lehr motor us to anchorage. Changed impellor next morning when everything cooler.

[sailorboy1]

You are probably right that since the pump had water it was ok and stayed lubricated. I put a loop in my generator line to ensure there would be water at the pump even though it is above the waterline.

[Kenomac]

I did the same with my generator last season, the impeller exploded after just a minute or two. The Yanmar impeller has been doing just fine, but last season I did the same thing as Dockhead at the beginning of the season, then the impeller self destructed a month later.

[DeepFrz]

How much damage did the yard cause?

[Dockhead]

I should probably mention that I have the SpeedSeal Life pump cover, with the Teflon disk. That might have helped in the closed sea cocks incident.

[svHyLyte]

Originally Posted by Dockhead

I should probably mention that I have the SpeedSeal Life pump cover, with the Teflon disk. That might have helped in the closed sea cocks incident.

In view of the relatively minor cost of a replacement impeller verses clearing impeller parts from one's cooling system, to say nothing of prospective damage to ones engine from overheating as a consequence of a shattered impeller, it might be wise to replace the impeller with new, just to be on the safe side, No?

I was taught to replace our impeller at the earlier of 12 months or 100 hours. While I have pushed that from time to time, on one occasion I regretted having done so. While newer materials may last somewhat longer, I would not care to be a "pioneer" with the matter considering that one can always tell who the pioneers are (from the arrows in their chests!), eh?

[bytownboy]

100 hours is by far the most conservative time span I have heard of for impellor life. Certainly far more conservative than what Yanmar recommends in my maintenance manual, but of course no harm can come from changing the impellor that often.

[bytownboy]

Further to my last post, the service manual calls for replacement every 600 hours.

[fryewe]

Perhaps your hull valve leaks past its seat, and the cooling and lubrication of the impeller continued even with the valve shut? With an unloaded engine at lower RPM, wouldn't take much flow to cool and lubricate it. 'Twould be worth checking if my boat...YMMV.

[boatbod]

Originally Posted by Dockhead

I should probably mention that I have the SpeedSeal Life pump cover, with the Teflon disk. That might have helped in the closed sea cocks incident.

Almost certainly this is what saved the impeller.

The number one enemy of impeller blades is heat, and that comes from excess friction between the blades and housing. Water lubrication normally suffices, but with a closed seacock it is only a matter of time before it boils dry and burns up. The Teflon parts of the speedseal cover reduce friction on the end plates but obviously not the impeller tips so you still only have limited run-dry time.

[Vasco]

Ran an impeller for nearly 2000 hours once. 4JH3E a bitch to get at. When replaced one vane was missing. Guess I was lucky. Always lots of water coming out of the exhaust. Yes 2000 hours.

[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.

[Vasco]

No the impeller was working pretty good. I found the missing vane in the oil cooler.

[Dockhead]

Originally Posted by bytownboy

Further to my last post, the service manual calls for replacement every 600 hours.

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

No harm in replacing more often -- except to your wallet!! Ouch!

But I think every second year is good for me. Every 400 to 500 hours.

And be more careful with the sea cocks.


Now, how many of you who change your impellers religiously, change your coolant with the same diligence? I change mine every other year. In my opinion this is really important on a boat, much more so than on a car, because of the risk of small amounts of salt getting into the fresh water side of the cooling system. The additives wear out, and I don't think it's determined by hours, but rather, by time.