Impeller impressions?

[MV Wanderlust]

We bought our boat in early August of this year. Before we picked it up, we paid a locally-respected mechanic to change the impellers in both mains. We weren't there at the time, we just paid the bill. This was in another part of our state.

During the ten day repositioning trip and subsequent local excursions, everything ran fine. A couple of weeks ago, we went to take it out and the Port engine overheated before we made it very far out of the marina. It only had 68 hours of running time since having the impellers changed at the previous marina. The diver service had just cleaned the hull and through-hulls five days before that outing. We shut the engine down and anchored while I went below to check the strainer. There was a little but of stuff in the strainers but no where near "blockage" level. Cleaned and reinstalled them but the overheating continued after restarting the engine so we returned to the dock.

Our new mechanic in our current marina investigated the overheating and found the Port engine impeller to be in really bad shape. (I had some trouble inserting photos this morning so had to resort to links, instead) This is what it looked like:
https://photos.google.com/share/AF1Q...dUTlZoci10Yl93

https://photos.google.com/share/AF1Q...dUTlZoci10Yl93

Opinions, please... If someone handed you this impeller, how old would you think it is? Is it possible it only has 68 hours on it? Can they deteriorate that quickly?

Thanks.

John

[Sailmonkey]

Two options,

1. That's a really old impeller!!

Or

2. Something was blocking the through hull and the impeller got hot enough to partly melt....if this is the case, the cover may be scored, as well as the pump seals toast.


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[MV Wanderlust]

Originally Posted by Sailmonkey

Two options,

1. That's a really old impeller!!

Or

2. Something was blocking the through hull and the impeller got hot enough to partly melt....if this is the case, the cover may be scored, as well as the pump seals toast.

Our new, local mechanic said nothing about the cover being scored or the pump seals being anything other than normal. A local hull cleaning service had just cleaned the hull and the through-hulls five days before the overheating incident. ...but anything could have happened.

[Suijin]

You can destroy an impeller in short order by running it dry (closed seacock, clogged strainer, etc.) but those pictures look distinctly to me like an old hardened impeller that disintegrated, not one that was run dry. Comparison with the undamaged one on the starboard engine would likely give you the best evidence of age.

[svHyLyte]

FWIW note that an impeller "ages" even when it's not in a pump. I have found that "spare" impellers in our spares locker have become very stiff and effectively unusable after protracted storage. (Accordingly, we don't keep spares unused for more than a year.) It's possible (although admittedly unlikely) that your first mechanic used too-old impellers (and if I were you, I'd check the other engine for the sake of the exercise). Moreover, on the rare occasions when we have used a mechanic to perform a service, they have always left or given us the old parts that were replaced so that I could see why something needed replacement. You may have gotten short changed, which I suspect is your own suspicion, but possibly not and have just suffered the unfortunately luck of the draw.

[Cheechako]

That looks like an old hardened impeller. Also the metal bushing in it looks too rust stained for 68 days. In the future always ask for the old parts.

[Stu Jackson]

Almost sounds like you're asking us to validate something we haven't witnessed first hand in order to allow you to go after the first mechanic. I ain't goin' there. I suggest you learn how to do the impeller swaps yourself. "Trusted marine mechanic" in many cases is an oxymoron. Perhaps you have physical disabilities that preclude you from doing that work, in which case, my apologies.

[MV Wanderlust]

Originally Posted by Stu Jackson

Almost sounds like you're asking us to validate something we haven't witnessed first hand in order to allow you to go after the first mechanic. I ain't goin' there. I suggest you learn how to do the impeller swaps yourself. "Trusted marine mechanic" in many cases is an oxymoron. Perhaps you have physical disabilities that preclude you from doing that work, in which case, my apologies.

No, Stu. If I decide to confront the original mechanic I will first take the impeller to a parts dealer so they can examine it first hand. Here, I was just asking for some opinions to see if I was being overly suspicious.

[Sailmonkey]

Originally Posted by JohnEasley

Our new, local mechanic said nothing about the cover being scored or the pump seals being anything other than normal. A local hull cleaning service had just cleaned the hull and the through-hulls five days before the overheating incident. ...but anything could have happened.

A plastic bag stuck to the intake can cause loss of water to the engine. If the seawater pump is painted, check for discoloration of the paint. This will point to running dry as well.


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[MV Wanderlust]

Yeah, that's a good point. The new mechanic found no discoloration on the pump housing. Here's something else I forgot to include: the mechanic took off the heat exchanger and found no parts and pieces of the impeller blades. None in the hoses, either. That's part of what made us suspicious. If the damage was very recent and catastrophic, like as if it happened all at once if a plastic bag was caught over the intake, I would have expected to see some pieces somewhere in the cooling system. But there was nothing. That made me suspect the impeller damage was due to gradual age and all of the pieces were flushed out through the exhaust.

[uncle stinkybob]

It looks like a typical run dry impeller to me. It got very hot for sure. imho.

[Snore]

Suggestion. Whenever I have work done and I will not be there--- I ask for the old parts.

[mickt243]

bits of impeller can also end up stuck in other places, like inside fuel coolers, power steering coolers, oil coolers, exhaust manifolds risers and elbows.... if not a fwc engine, can also get caught up inside the engine block causing hotspots....

you really need to fully investigate where all the missing bits went..... otherwise you may well end up with more overheats etc.

[MV Wanderlust]

Originally Posted by mickt243

bits of impeller can also end up stuck in other places, like inside fuel coolers, power steering coolers, oil coolers, exhaust manifolds risers and elbows.... if not a fwc engine, can also get caught up inside the engine block causing hotspots....

you really need to fully investigate where all the missing bits went..... otherwise you may well end up with more overheats etc.

And that's exactly what happened, Mick. Went to the boat on Sunday and ran the engine for about half an hour. We shut it off before it got to the point of the alarm going off but it got up slightly above 200 degrees when running at 1000 rpm. We sped it up to 2000 rpm to see if more water would cool it down. That didn't work. Backing it down to idle didn't help, either.

We've asked the diver service to double check that through-hull to ensure nothing it obstructing it. And we advised the mechanic of what happened.

At this point, I'm thinking either there is some obstruction in the hoses or heat exchanger or the thermostat is stuck (but it seems like it would have overheated faster than half an hour if that were the issue) or some articles have talked about an obstruction in something called the elbow. Hoping the mechanic can get on it this week.

[HappyMdRSailor]

Hi John,

ANYTHING could be possible... It certainly looks like a very old brittle impeller, but... As others have stated... Totally possible from starved running, totally possible from aging in the box... Since you aren't out anything but a typical "boat ownership expense", (you're still 1 shy of the same repair trifecta) and not a catastrophic expense... I would suggest the word for communicating with the previous mech not be "confront"

I'd go the angle of... "Hey guys... FYI, some of your stock may be bad, I had one let go at 68hrs"

Yea... sounds like you have rubber bits stuck in coolers and exchangers... Unless you're more comfortable with a pen and checkbook vs. a rag and screwdriver, it may be time to roll up your sleeves...