My Hunter 42 Passage has an Onan 8KW Generator which has run great until last weekend when I started it and had no water discharge from the raw water pump. I changed the impeller, which I admit was past due, changed the gasket and the face plate, still no water discharge. Removed both hoses, ran water down the intake hose to see if the intake may be clogged, no problem, hooked up a short hose to the intake side, filled a bucket with water and placed the input and output hose in the bucket. Ran the genset, no water being pumped. The mechanic at our marina, suggested the back plate of the pump is worn and therefore the impeller cannot make a seal and cannot establish enough suction to draw water. He also stated he believes the pump is obsolete and may cost upward of $1,200 to replace the pump. Have any of you had this issue and if so what was your remedy? My genset has about 2500 hours and the pump was manufactured by Oberdorfer Pumps in Syracuse, NY, USA.
Hunter Passage Raw water pump
- Thread starter BellaSogno9119
- Start date
Our 1991 Onan Genset has about 400 hours on it; about 235 when we took possession in 2002. The two occasions that no sea water discharged were when, after cleaning the sea water strainer, I did not get a good lid seal. The other was when the pump sucked in a gob of marine gunk from a filthy Ganges anchorage and clogged the strainer. In the process of trouble shooting I replaced the original impeller that was due. After priming the pump (poured water down the hose where it enters the mixer) it pumped just fine. That was the only time I needed to prime the pump.
Whether your mechanic is correct about the backing plate, check it again for wear. That many hours does not seem excessive to me. The backing plate on ours had virtually no wear.
Whether your mechanic is correct about the backing plate, check it again for wear. That many hours does not seem excessive to me. The backing plate on ours had virtually no wear.
I do not have an ONAN, I have a fisher panda. My FP has about 1000 hours on it. Cooling water/ priming has been problematic for the last 500 hours. I believe that I have it fixed now.
In most raw water pumps, there is a shaft seal pressed into the back to the housing that seals the shaft that spins the impeller. This shaft seal is seldom replaced. Replace it regularly and you may have solved the problem.
The other issue is that most gen sets are installed above the water line. So if you have the smallest leak, on the cooling side, the water in the pick up line will flow back to the water line, and the next time you start it the head pressure maybe too much for the pump to overcome.......no cooling water. The FP solution that was buried in their install manual, was to install a foot valve( check valve) at the through hull, to keep the pump primed. I was worried about flooding, but our FP has a siphon break installed and working. So not an issue. I am again happy with my FP.....no more priming needed.
As others have said, new impeller, new gasket, new shaft seal, smooth cover plate......and maybe a check valve.
Another note on impellers. I tried the blue run dry impellers, and they performed much poorer that the black impellers. Priming was almost impossible with the blue one. On the Yanmar, the blue work fine as the pump is below the water line.
Good luck.
In most raw water pumps, there is a shaft seal pressed into the back to the housing that seals the shaft that spins the impeller. This shaft seal is seldom replaced. Replace it regularly and you may have solved the problem.
The other issue is that most gen sets are installed above the water line. So if you have the smallest leak, on the cooling side, the water in the pick up line will flow back to the water line, and the next time you start it the head pressure maybe too much for the pump to overcome.......no cooling water. The FP solution that was buried in their install manual, was to install a foot valve( check valve) at the through hull, to keep the pump primed. I was worried about flooding, but our FP has a siphon break installed and working. So not an issue. I am again happy with my FP.....no more priming needed.
As others have said, new impeller, new gasket, new shaft seal, smooth cover plate......and maybe a check valve.
Another note on impellers. I tried the blue run dry impellers, and they performed much poorer that the black impellers. Priming was almost impossible with the blue one. On the Yanmar, the blue work fine as the pump is below the water line.
Good luck.
How about a clog some place maybe a piece of the impeller or maybe dirty or clogged heat exchanger,recently a friend with a northern lights gen and both is like like weeks new to him shut down and over heated 15 minutes after starting and the water pump was so hot could not take screws off the cover plate and after hours of trying and checking all hoses and the thru hull to make sure getting water we started it up and with in seconds it had water pumping out side of boat and we think it got air locked maybe the strainer was sucking air.
Thank you all for your insight. Sounds like it me be a priming problem, though I would have thought when I removed both input and exit hoses, connected a one foot house to the input and placed it in a full bucket of water the pump would have been able to prime itself. I even tried to put some gasket sealer on the cover plate gasket and the strainer gasket to ensure I had no air leaks at those points... Will not be back to the boat until the weekend. I'll try to prime the system with the seacock closed and see if the pump draws. Thanks again.
Maybe try starting engine first and than put a water hose in the intake hose to the pump and than see if it pumps.
Nick
Nick
Take the faceplate off. Goose the motor with the fuel off. Make sure the impeller turns.
Make sure the metal rings are installed on both sides of the impeller.
Put a little Vaseline on the impeller to lube and help it prime for the first time. After that it will be wet unless it sits a long time.
Those pumps are self priming. Even a little above the waterline. Unless you have an air intake leak in a hose, which may not also leak water. Tighten hose clamps.
Last: $1,200 for a new pump is ludicrous. A new one is about $300, and it's 2 hoses and 4 bolts to install.
I'm doing mine right now out of amazing coincidence. It's an Oberdorfer, needs new seals. Took me 8 minutes to get it off. Another 4 minutes to take it apart. Now have to get the bearing and seals pressed out and new ones in. $60 for parts kit. .... sorry meandering.
Edit: DO NOT start the engine with the seacock closed. It will do nothing, except damage your impeller.
Make sure the metal rings are installed on both sides of the impeller.
Put a little Vaseline on the impeller to lube and help it prime for the first time. After that it will be wet unless it sits a long time.
Those pumps are self priming. Even a little above the waterline. Unless you have an air intake leak in a hose, which may not also leak water. Tighten hose clamps.
Last: $1,200 for a new pump is ludicrous. A new one is about $300, and it's 2 hoses and 4 bolts to install.
I'm doing mine right now out of amazing coincidence. It's an Oberdorfer, needs new seals. Took me 8 minutes to get it off. Another 4 minutes to take it apart. Now have to get the bearing and seals pressed out and new ones in. $60 for parts kit. .... sorry meandering.
Edit: DO NOT start the engine with the seacock closed. It will do nothing, except damage your impeller.
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Was the water pump leaking at all before this problem? (I like where Skipper is taking you on this.)
I"d use teflon greese without petroleum (jelly). Example "Superlube".
The "goose" the engine is important. Don't start the generator without water flowing through it. The impeller you have in there will not last very long if it's spinning dry -- and the generator won't like being overheated.
The pump is positive displacement pump and should be self-priming. (It worked before, something happened).
Was the impeller your replaced missing blades or parts of blades? "past due". You need to openup the heat exchanger and see if there is impeller pieces blocking things next.
Whoever suggested $1200 seems crazy to me. I'm assuming that your generator was working and this is the "new" discrete problem.
I"d use teflon greese without petroleum (jelly). Example "Superlube".
The "goose" the engine is important. Don't start the generator without water flowing through it. The impeller you have in there will not last very long if it's spinning dry -- and the generator won't like being overheated.
The pump is positive displacement pump and should be self-priming. (It worked before, something happened).
Was the impeller your replaced missing blades or parts of blades? "past due". You need to openup the heat exchanger and see if there is impeller pieces blocking things next.
Whoever suggested $1200 seems crazy to me. I'm assuming that your generator was working and this is the "new" discrete problem.
The 8kw Onan on our boat was designed to operate in a remote, unattended location. It has three sensors; exhaust temperature, oil pressure and engine temperature. Any of these sensors that detects a problem will trip a circuit breaker that automatically shuts down the engine and present an alarm before engine damage occurs. Once the problem has been located and corrected, you can reset the circuit breaker and restart the engine. That breaker is located on the engine control panel.
Well, I was finally able to get back to the boat and this project. Sometimes life and the job just get in the way... I was able to eliminate the pump as the problem by connecting the engine intake line to the Genset impeller intake. My genset sits above the engine and the engine intake hose was plenty long enough. Prime the line and the old pump worked like a charm!!! I then disconnected the hose between the thru hull and the strainer to see if I had a clog intake or line. Opened the thru hull valve and had plenty of water. I was also able to blow into the hose from the impeller intake to the strainer and had no blockage there either. I looked again at the strainer cover and noticed the original cork gasket was very hard. Went to an auto parts store, bought a sheet of gasket cork and made a new gasket. Put it all back together, primed the line and eureka, plenty of water at the output and the genset ran like a champ once again. Thank you all for your input.
Some times things are hard and had a friend have his Gen run hot after running only 30 minutes and he spent hours checking all hoses and could not find anything and after putting everything back together it ran fine he thinks the strainer was not closed and maybe sucking air but been running fine ever since.
Thank goodness you got it fixed with out too much $$$$.
Nick
Thank goodness you got it fixed with out too much $$$$.
Nick