Generator impeller operation question, please

[Streff]

I have a 20KW Kohler. For a few days it started throwing white smoke but never overheated. I cleaned the strainer, I opened the impeller and it looked perfect with less than 30hrs on it. Everything else looked fine. A few days later, the gen overheated and stopped. With my temp gun, the gen was at 210F & the impeller case registered 180F. I took out the impeller housing and the impeller was chewed up and looked like it melted. I cleaned & fished out its pieces. Installed a new impeller, filled the system with water to avoid potential airlock. I kept the end of the outlet hose from the impeller disconnected and started the gen. After a 90sec, I did not see any sea water being circulated by the impeller.

We are anchored in an area with real heavy kelp. Thought maybe something is blocking the through hull. I then removed the hose from the strainer and inserted it in a 5 gallon of water with a clear terminal hose to observe. The impeller was not able to pull any water. So unlikely that the trough hull is blocked. Next I opened the impeller plate to make sure that it’s turning. Observed it rotating fine.

My question is how long would it take the impeller to pull water across 3 feet of hose from a strainer that is 18” below the impeller? Should I give it more time see it will eventually pull water.

At this point I am just stumped. All hose connections are open & clear of debris, impeller is rotating but it’s not circulating sea water.

Any comments or ideas would be greatly appreciated.

Streff

 

[Comodave]

It should start pumping almost immediately. Maybe a worn cover plate or worn cam.

 

[O C Diver]

If you just replaced an impeller 30 hours ago and there were bits and pieces missing from the impeller, did you remove them from the heat exchanger? Might also want to check for impeller bits and debris in the pump output tube and the hose between the water pump and the heat exchanger.

In addition, any chance the heat exchanger could be plugged with growth?

Also, the end plate, the wear plate, or the cam could be worn enough to prevent the impeller from drawing a vacuum.

Ted

 

[High Wire]

It should start pumping almost immediately. Maybe a worn cover plate or worn cam.

Agree, seconds.
Possible air leak on the cover gasket, strainer cover gasket, or a hose connector. Worn cover or back plate or cam.
After start, put your fingers lightly on the pump cover. It should be getting cold not hot. If hotter shutdown immediately.

 

[Larry Lilly]

Perhaps it would be better to fill the thru-hull strainer & hose prior to starting the motor. When I come out of winter storage, I prime/fill all my engine strainers so they have an instant supply of lubricating water. Cheers

 

[Juliet 15]

I'd check the hose between the thru-hull and the strainer for kinks, a blockage, or a cut (air leak).

 

[Juliet 15]

My bad. I meant check the hose between the thru hull and the impeller housing...

 

[jgwinks]

Look at the inside surface of the pump cover plate. A little scoring is normal and happens as soon as you first start it up. Deep grooves and any "step" around the edges could reduce it's efficiency to the point of not pumping at all. If the outside of the plate is smooth with no writing or anything stamped in, you can just turn it over. Otherwise you can sand and polish the inside surface smooth. Same thing can happen to the back side of the pump chamber, but you can't repair that, need to replace the whole pump. One of the things I look at on every engine room check is the pump cover plate temperatures, they should be approximately the same as the sea water. If they're hot, they're not pumping.

 

[Lepke]

Rubber impeller pumps almost always pump, even with a worn housing or impeller. If you have free flowing water from the seacock and hose, I'd look at the HE As O C Diver said. If that's clear, then from the HE to the discharge. Could be rusted up exhaust elbow where water enters.
My mains pull about 5' from the seacock thru the strainer. I usually start my engines from the engineroom. By the time I get my finger off the start button, the hose and pump are already cold.
Lube the housing and end plate. It increases suction.

 

[jgwinks]

That's not been my experience, especially with the blue "Run Dry" impellers. Any wear in the pump and they lose thier seal and don't move water, at least not very well.

 

[Streff]

Thank you all for the insightful comments. I went back today and checked again all hoses, HE, etc. they are all clear and open. I will open the strainer and tighten again on its gasket. I can convince myself that the impeller housing cover could be worn. I have the usual o-ring (it’s an older one) but not the paper gasket. The last 2 impellers came with a bunch of o-rings and paper gaskets but none of them fit. I will try to find a new o-ring. I am getting another backup impeller tomorrow.. hopefully it will come with a compatible paper gasket.

I don’t know where to find the Cam?? But I will look it up. I am trying to find a service manual. I am not anywhere near a Kohler power systems dealer. But the motor is a Yanmar.

Thanks so much

Streff

 

[mvweebles]

I don’t know where to find the Cam?? But I will look it up. I am trying to find a service manual. I am not anywhere near a Kohler power systems dealer. But the motor is a Yanmar.

See attached generic picture. The "Cam" it " Lobe" is at the 12-o'clock region and serves to compress the volume thereby pumping it. It takes a LOT of hours (or abuse or sand) to wear this down. The reason Lepke observed these pumps almost always work is it's really hard to lose so much volume (via worn cam or excess play between impellor and cover plate) that it can't pull water. If your pump is well above waterline, maybe, but if there's a correctly sized impellor, it's hard to keep one of these pumps from pumping.

I couldn't follow your comments on o-rings and gaskets, but it sounds like you have spare and disparate parts. Are you sure you have the right impellor? I don't mean to trivialize a few hundred bucks, but if all else is clear, maybe replace the pump? Cheaper than a service call.

Peter

 

[Simi 60]

Go electric
Best thing we ever did on the Genset
5 years trouble free, no impeller changes, no blood letting, no swearing

 

[murofrelwart]

Go electric
Best thing we ever did on the Genset
5 years trouble free, no impeller changes, no blood letting, no swearing

Details please.

 

[mvweebles]

Details please.

Idea is that you take something like a 120vac magnetic pump often used for AC circulation and bypass the mechanical pump on the generator. When the generator turns on, it activates 120vac and the pump starts simultaneously. In effect, you are replacing a gear-driven pump off a diesel engine with an electric motor driven pump off the power head of a generator. It works fine until it doesn't and has the side benefit of immediately voiding manufacturers warranty if that matters. It is however a great temp fix of you have enough hose to reroute raw water to an external pump.

Peter

 

[rslifkin]

Go electric
Best thing we ever did on the Genset
5 years trouble free, no impeller changes, no blood letting, no swearing

I'll second the details request, as good quality impellers for the pump on my genset are starting to become very hard to find.

 

[Simi 60]

I'll second the details request, as good quality impellers for the pump on my genset are starting to become very hard to find.

First you need to figure out water output of your existing setup
Then match to a continuously rated eectric pump

For us with a 7 kVA Kubota based Genset an MD30 magnetic drive pump was a good match - $140 delivered on eBay
This one
https://www.ebay.com.au/itm/1921710...TJfRLOEI9ESikY7s2scSDqY8rP-awenBoCR3gQAvD_BwE

Various sizes available, MD10 to MD???
It's the same same pump I had used for brewing for over 10 years
And now, the same pump I use as feed pump for the watermaker, so with 3 onboard, we essentially have spares

It's continuously rated and chemical rated so saltwater is not an issue
Inlet and outlet is same as genset
It must be mounted below waterline which our Genset is anyway.

I made an aluminium plate out of 3mm to block off shaft driven pump hole on engine, gasket sealant, bolted in and done.

For power supply for us full time cruising the easiest way was to buy a builders power box with rcd for $60 on eBay and wire that in to power out on Genset head and plug pump intro power box.
I got a 15 amp dual plug so as to have a 15amp plug in ER to run welder if needed
https://www.ebay.com.au/itm/2555802...83kPkhIpRS7zUoBXEDF2g4z9gvvB|tkp:BFBMsubxwb5g

Genset starts and within seconds power is supplied to power box and water is squirting out the side.

 

[Streff]

I was able to get a new impeller with a proper O ring today. I cleaned the cover plate then I opened the strainer and opened the thru-hull.. all I was getting was a slow dribble. I am not sure what I expected but definitely more flow than what was coming out. I looked deep in the thru-hull with borescope. I saw sea grass. Not having compressed air or pressure washer, I vacuumed the water out from the end of the hose coming from the strainer. It was slow coming but eventually water started coming up but still slow. I was using a 5HP shop vac. Using wood skewers and a thin long brush, I tried to clean the sea grass, cut it disrupted, etc. then vacuumed again with the vacuum thin nozzle.

The water flow was better but not enough to prime the get the impeller going. Next I am going to try to blow with the shopvac as a last resort. I am not sure how else to dissolve or clear the sea grass clog.. A diver wont be available for several days. The tide has been pretty low over the last 3 weeks in the PNW. Today its the lowest that it has been in 10 years. The kelp and sea grass must have gotten pretty close to the thru-hull.

Any comments or ideas on cleaning a clogged thru-hull would be much appreciated c

I happen to have a backup generator from Lowes (not the suitcase type). I relocated to wide open anchorage to run it.. it so so loud and lots of exhaust.. not ideal to run on a boat.

Thank you again for the comments and advice.

Streff

 

[Comodave]

Sounds like you found the problem, now just to get it cleaned out.

 

[mvweebles]

Garden hose with duct tape around the end to make tight fit into hose from seacock. Hose clamp it and turn on pressure. May take a minute or two, and there may be a pretty loud thud when the obstruction breaks free. Tough to beat 40 psi of water pressure.

Good luck.

Peter

 

[hmason]

Try working a stiff bristled bottle brush in and out of the through hull with the seacock opened.

 

[Streff]

Problem seems to have been resolved. Will fully test tomorrow. I tried a bottle brush with sea cock open… that certainly increased the flow some. Next was the Shopvac to push air into the thru-hull.. some additional improvement. But the impeller was still not pumping. Thank you mvweeble for the recommendation to push water pressure. It gave the idea to use my motorhome VIAIR high pressure tire inflator, which I still had on the boat in case we wanted to fully winterized. I set it for 50psi, Holly smokes that pushed air with massive air bubbles under the boat.. next I pushed water through.. once I cut the water, I can hear the strainer filling very quickly. I tried the impeller with its outlet hose open to monitor it and next came water circulation. What a relief!

We finally had 3 nice sunny days and I spent them in the ER. I learned to never again anchor in areas with lots of sea grass & kelp especially when tides are so very low this season.

Thank you all very much for the ideas and recommendations. Much appreciated.

Streff

 

[Duetto]

answer to the 110v pump. i've installed it on 2 boats with different generators. wire directly to genset 110 output. genset starts, pump starts. 110 stops, pumps stops. one issue is that pump location has to be about 1' below water line.

after 15 yrs on one boat and 10 on the other, it's a winner.

 

[Streff]

To wrap up the testing. Gen worked fine last night, held its temp..but produced white smoke that looked very much like steam. I think I detected a pin hole in the mixing elbow which could possibly contribute to the steam smoke?? I am not sure.

I am making plan to install an electric 110 pump. Just need to determine output of current impeller pump.

Streff

 

[bill.kimbell]

Garden hose with duct tape around the end to make tight fit into hose from seacock. Hose clamp it and turn on pressure. May take a minute or two, and there may be a pretty loud thud when the obstruction breaks free. Tough to beat 40 psi of water pressure.

Good luck.

Peter

Water pressure far superior to air pressure. Water doesn't compress. If all else fails, fill dinghy foot pump w water. You'll have plenty of force to clear most clogs.

 

[ronobrien]

I have a 20KW Kohler. For a few days it started throwing white smoke but never overheated. I cleaned the strainer, I opened the impeller and it looked perfect with less than 30hrs on it. Everything else looked fine. A few days later, the gen overheated and stopped. With my temp gun, the gen was at 210F & the impeller case registered 180F. I took out the impeller housing and the impeller was chewed up and looked like it melted. I cleaned & fished out its pieces. Installed a new impeller, filled the system with water to avoid potential airlock. I kept the end of the outlet hose from the impeller disconnected and started the gen. After a 90sec, I did not see any sea water being circulated by the impeller.

We are anchored in an area with real heavy kelp. Thought maybe something is blocking the through hull. I then removed the hose from the strainer and inserted it in a 5 gallon of water with a clear terminal hose to observe. The impeller was not able to pull any water. So unlikely that the trough hull is blocked. Next I opened the impeller plate to make sure that it’s turning. Observed it rotating fine.

My question is how long would it take the impeller to pull water across 3 feet of hose from a strainer that is 18” below the impeller? Should I give it more time see it will eventually pull water.

At this point I am just stumped. All hose connections are open & clear of debris, impeller is rotating but it’s not circulating sea water.

Any comments or ideas would be greatly appreciated.

Streff

I have heard of a different solution to the impeller issue. A 120VAC A/C raw water pump is wired to the gen and the impeller is bypassed. As soon as the gen starts the pump starts and provides the raw water to the system. These are, in general, less prone to failure that the impellers, particularly if they are starved for water as they are centrifugal pumps. You would need to verify that the pump has an adequate output for the cooling requirement of the generator. Not an answer to you question, but just some food for thought.

 

[Salty Suzy]

White smokw

White smoke could be from blown head gasket. Possibly from overheating.

 

[AKShane]

Is the valve on the discharge side of your exhaust system open? If it won't pull water out of a bucket I would look down stream for a clog.

 

[rgano]

Is there a screen of any sort on the exterior of the through-hull? If the grass and junk has gotten inside that, you will not easily get rid of it without removing the screen.

 

[Streff]

Just got back in cell service territory. Thank you all for the comments. For the last 8 days, the genset worked fine. Little smoke but pretty smelly. Following purging the TH with water and air pressure, the flow was decent enough for the unit to operate but the water flow increased on its own over the following 4 days. Interesting.

There is no valve on the exhaust water flow. So it’s straight through from HE..mixing elbow.. muffler then out the side.

Still working on replacing the mixing elbow, all available new elbows don’t have a plug for the exhaust temp sensor. New elbows are make of SS which makes the welding of a plug more complicated. I am try to seal the pinhole in the elbow with muffler putty?? Until I get a properly configured elbow.

Thank all again for the very valuable input.

Streff