Baffling, Maddening Impeller Problem

[Dockhead]

A couple of days ago I overheated my Kohler diesel genset. A big clump of seaweed had gotten into the raw water strainer and clogged it.

I unclogged it, topped off the cooling system, and it ran perfectly well. But I noticed that the coolant had become sludgy and decided to flush it.

That's when my real problems began!

It overheated again. I am guessing an airlock problem, but I haven't gotten that far yet. Because I decided to check the impeller, verified that it was fine, put it back together again, started it, and -- forgot to open the sea cock. It melted down the impeller. Oh brother.

So I swapped it out for the old one, also in good shape. Started it up, and noticed that the exhaust was getting hot -- no raw water flow. Noticed that the water pump">raw water pump was getting hot. Oh, damn. Shut it down, opened up the raw water pump -- saw that the impeller had its blades turned half one way, half the other way.

Thought -- I put it in backwards. So I took out the impeller, put it back in with all the blades facing the right way. Started it up - and felt the raw water pump getting hot again. Damn! Opened it up and -- again half the blades facing one way, half the other way. What the ??!!

Checked the manual -- indeed my understanding of the direction of rotation must be correct -- counterclockwise as viewed from the generator side.

Turned the raw water pump by hand, and noticed that I could turn it either way, and the blades flipped over immediately, all facing the correct way for either direction of rotation.

So WTF????? I think about doing it one more time -- orienting the blades backwards, in case both I and the manual are wrong about the direction of rotation. But something tells me this is not it . . . .

Anyone ever experience such a thing???????

[mrm]

A first thought: backpressure from some blockage?

[bstreep]

Wow, this is getting old, isn't it? Kinda deja-vu for me - we have a Kohler as well, and when I cleaned the strainer on Monday after a weekend of use... A big old clump of seaweed.

Couple of things: As noted, make sure you don't have a blockage elsewhere. If you open up the seacock, are you getting water supply to the pump? Depending on your strainer, they don't get EVERYTHING. When you burnt up your prior impeller, did you lose any fins? Could you have spun out the impeller? When you turn the water pump by hand it will spin, but at high speed it won't push any water.

[Dockhead]

Originally Posted by bstreep

Wow, this is getting old, isn't it? Kinda deja-vu for me - we have a Kohler as well, and when I cleaned the strainer on Monday after a weekend of use... A big old clump of seaweed.

Couple of things: As noted, make sure you don't have a blockage elsewhere. If you open up the seacock, are you getting water supply to the pump? Depending on your strainer, they don't get EVERYTHING. When you burnt up your prior impeller, did you lose any fins? Could you have spun out the impeller? When you turn the water pump by hand it will spin, but at high speed it won't push any water.

Anybody have any insight into why the impeller blades turn in different directions? Seems totally bizarre.

Yes, getting water to the pump -- the intake and hose are clear. I don't know about downstream, but surely that wouldn't cause the raw water pump to heat up like that.

[Stu Jackson]

It sounds like the blades aren't turning when the pump is closed up. This usually means that the blades are loose from the shaft. Get a new impeller.

[daddle]

If it gets hot, the raw water pump is likely turning with no water flow. Perhaps the engine turns backwards a bit on shutdown. That could reverse a few blades. But you have a clog somewhere. Overheating the pump may have ruined the shaft seal. That will be obvious when you get the water flowing.

[jongleur]

The impeller's rubber is probably not connected to its own shaft. Blades are probably not turning at all.

[Dockhead]

Blades turn -- I have turned over the engine with the impeller cover off. I have figured out that the blades direction is a red herring -- the engine kicks back at shutdown, I think, turning the blades.

I guess I have a clog downstream of the pump and water is not going through -- is that enough to make the raw water pump heat up like that?

Either that, or the old impeller is swollen and not fitting right, or maybe is not even the right impeller (unlikely).

I can't think of any other possible reason. There is water inside the raw water pump, so it's not simply running dry.

[Stu Jackson]

You may have a partially clogged inlet water strainer or a clogged intake seacock or hole. Check those out, too. The strainer is easy. You may need to use another method to check the seacock and hole. I've used a dinghy foot pump to blow back through and remove clogs.

The "pre-positioning" of impeller blades in pumps is an urban myth and quite unnecessary. Once the pump starts the blades will seat properly.

Have you checked that the impeller is secure on its shaft?

Is the inside face of the pump flat? Sometimes prime is lost is the inside face gets scored.

If you think you have a clog downstream of the pump, then work on those components. Step-by-step, section-by-section. Only YOU can do that, 'cuz we're not there with you.

Good luck.

[perchance]

With the pump cover off roll the engine over to verify the direction of rotation then scribe an arrow on the cover.

[sabray]

I was thinking the impeller is the wrong size. Mine is very hard to twist in. Guess its possible the engine is kicking back enough to reverse the direction but I am surprised if that's the case.

[David M]

Are any of your vanes missing? Vanes broken off an impeller can cause blockage. This can mean taking apart hoses or other parts upstream of the impeller housing....as far as the heat exchanger.

[captain465]

+1 on the suggestion regarding broken bits of an old impeller causing a downstream blockage. Not enough water flow and the impeller body starts to heat up. Also possible that the heat exchanger core is clogged with minerals from long term use.....how old is the engine???
Please let us know your results.

[bstreep]

Is the engine driving this a Yanmar (like maybe 17hp)? If so, my impeller is also a snug fit. When I cleaned out the strainer, I also noted about an 80% clog on the intake. You may be getting SOME intake water, but not all of it? Try fitting a fw garden hose on the intake hose, and pushing water backwards.

[Andina Marie]

A couple of things to watch. If the impeller disintegrated there can be pieces trapped in the heat exchanger partially blocking it A strong backward flush can sometimes clear them but disassembly is the best assurance.

A warning on using those "lifetime self lubricating" impellers that are not supposed to self destruct if run dry. I thought that is a great idea but they didn't last a week. What was happening is after the engine was turned off water sitting in the heat exchanger would heat up and drain back slowly into the raw water pump and it was hot enough to soften the impeller so it no longer had any sealing pressure on the housing.