Question: is it possible for a raw water pump, in this case an Oberdorfer on a Universal M25XP, to be 'bad' without leaking water? The impeller & gasket have been replaced, water is getting to the pump from the strainer, but no output. I have checked all the lines into and out of the pump for obstructions. Heat exchanger, exhaust elbow, etc. all clear to the aqua muffler. Everything seems okay, but no water coming out of the stern (and with that an overheating engine).
Raw water pump question
- Thread starter knotoldyet
- Start date
Sounds like a total blockage so one would think likely not a HX problem but a hose/ passage way blockage. Did it develop suddenly like a blocked thru hull or slowly like a blocked exhaust? Are you sure you have the right impeller and is it turning? Most obstructions in HX and block let some water pass. I would start at the inlet "follow the flow" as an overheated hose can look good from the outside but be delaminated on the inside.
Good luck, let us know how you make out.
Good luck, let us know how you make out.
This has been an ongoing problem for a couple of weeks now. I thought it was fixed; plenty of water from the stern exhaust; then it stopped working again. This time no water at all. Heat exchanger is clean and clear and the hoses are open. I am as sure as I can be it is the correct impeller. I have checked references and manual - even tried 2 or 3 impellers in case I had a bad impeller. No water is getting as far as the aqua muffler, so I think it is likely okay. I think it is either a bad pump (hence my initial question) or some kind of obstruction at the intake that increases when the vacuum increases with added power from the motor. The pump looks immaculate, but as Sefuller suggests, it could be a gap between the impeller and cover plate. This pump has the paper gasket. The pump shaft appears to connect directly to the engine, so the shaft must be turning if the engine is turning, right??
Some have reported impellers spinning on shafts. Only way to tell is to take the faceplate off and check by running the engine for a few moments.
Oberdorfers are very good pumps. They REQUIRE that the faceplate be as perfectly smooth as you can make it. I've sanded mine down and even gone & bought new ones.
Oberdorfers are very good pumps. They REQUIRE that the faceplate be as perfectly smooth as you can make it. I've sanded mine down and even gone & bought new ones.
Have you changed the impeller or removed the pump recently? The earlier versions of this pump have an adapter to engage the pump shaft with the cam shaft. If the pump shaft pulls out when changing the impeller it may disengage the adapter. You have to remove the pump to re-engaged it. It's real easy, just two bolts.
Other causes may be too thick a gasket or scored cover plate or back surface of the pump. If its the back surface that's scored, you have to replace the pump.
Don't get a new one from Universal. They're available from other sources like Depco or Moyer Marine for a fraction of the price.
Are you using the blue nitrile run-dry impellers? I've had terrible luck with those. Seems they won't pump if the pump housing is at all worn. I've never gotten one to work, and that has been on several different pumps. Stick with the black rubber ones.
Other causes may be too thick a gasket or scored cover plate or back surface of the pump. If its the back surface that's scored, you have to replace the pump.
Don't get a new one from Universal. They're available from other sources like Depco or Moyer Marine for a fraction of the price.
Are you using the blue nitrile run-dry impellers? I've had terrible luck with those. Seems they won't pump if the pump housing is at all worn. I've never gotten one to work, and that has been on several different pumps. Stick with the black rubber ones.
How about disconnecting the output hose of the pump and add more hose
so to go into a bucket and this way check how much the pump is actually
pumping water into a bucket by letting engine run just a few minutes before engine
starts getting hot.
Nick
so to go into a bucket and this way check how much the pump is actually
pumping water into a bucket by letting engine run just a few minutes before engine
starts getting hot.
Nick
Yes, I have replaced the impeller recently. The old one was chewed up quite a bit. I replaced it, along with the gasket. I thought perhaps pieces were obstructing the flow, so I have essentially disassembled everything from strainer to muffler. I am using the black impellers. I have one of the blue ones, and tried it, but no luck. So I went back to the black ones. This pump has a shaft that comes out with the impeller. There is a flat protrusion at the engine end of the shaft that engages with female version in the engine. Capt jgw - you mention an adapter. I'm not sure if this has one or not. The shaft appears to slide right into the pump, then a 1/4 turn or so, it locks into the engine and goes in slightly further into place. Seadaddler - I have tried your suggestion. Initially, when the problem arose, I got some water, but now there is none. I ordered a new pump today from Depco (very nice, helpful people). Hopefully that will fix the issue.
If yours has a single flat projection that's the newer kind with no adapter. If its a slot, there is an adapter.
If the old impeller lost vanes, they're in there somewhere plugging things up.
If the old impeller lost vanes, they're in there somewhere plugging things up.
Thanks for the input, folks. Greatly appreciated. I did find some parts of the impeller along with other odds and ends. Gravel, sand, Jimmy Hoffa's cuff links, etc. Mostly in the HX. At this point everything is clear of obstructions to the best of my knowledge. It is though all is in working order until the engine fires up, then no water coming out of the stern exhaust. Just air, fumes and gurgling noises. I have pulled hoses with engine running, and no water is being moved through the system. Comes back to either the pump or an obstruction at the thru hull when under power. I'd rather be sailing.
Have you checked the elbow at the outlet of the pump that go to the hose to the HX?
Have you tried taking the hose off the through hull and momentarily opening it? Water should gush in at a high rate. Could be the TH is plugged. Is there a screen or grate on the outside? Those can plug up with growth.
I did check the elbow on the output side of the pump. Basically everything has been checked except the thru hull itself and the intake side of the screen strainer. This is why I believe it is the pump or thru hull, although I was wrong once before, and no doubt it could happen again. The strainer has been clear. I am a relatively new owner of this boat (Catalina 30), so I don't know exactly what type thru hull intake it has. An earlier thread suggested it could be a plastic bag or other debris that is intermittent and/or closes the opening under power. I am a little hesitant to get too aggressive with the thru hull while she is in the water. One YouTube video shows using a Shop Vac to blow out the thru hull from inside the vessel. Anyone have experience with that? Maybe I need to go swimming?
Capt jgw has good advice. Take off the hose on the thru-hull and momentarily open the valve to check the flow. If it makes you feel better, attach another hose to the thru-hull and put it in a shallow bucket. If the bucket is low you will be below the waterline. You should have a solid stream of water. If there is not an external or built-in strainer, you can lead the hose straight up above the water line and then plunge it with a drain snake to clear any debris. If you have an outside strainer, you may need to dive on it. Do you have any pictures of the outside hull that might show the thru-hull?
No pictures of the hull from the outside. I did try to clear the area with a brush from dockside. Of course, I couldn't see it, but I did feel some light resistance as though some kind of strainer is on the outside. The thru hull valve is directly above the thru hull, then the internal screen strainer is attached to the valve. There is no hose between the strainer and thru hull. There is a hose from the strainer to the pump. I am getting water out of the strainer. It does not have much pressure; but some volume. I don't really know what I should expect from just outside water pressure. I can disconnect the hose from the pump, then lift it above the strainer to get above the water line - then use air pressure to force water out as suggested. I will try that later this week when I get back to the dock. Thanks again folks. I sincerely appreciate the info and suggestions.
Put the hose going into the pump in a bucket of water. Put the hose leaving the pump in an empty bucket and start the engine. This will tell you if the pump works. Your hose from your strainer might not be reinforced marine hose and it could collapse from the vacuum of the pump.
Sorry for the delay and update. All is working well now. It was the raw water pump that was the problem. I replaced it and everything works as it should. Plenty of water out the stern exhaust. Thanks, jibes138 and others for excellent suggestions. BTW, I did flush the through hull with a shop vac in blower setting. Worked perfectly. If you hold the hose above the water line, then apply air, it won't spill a drop of water inside the boat.
So now I have a new, related question. Now that the engine is cooling properly, should I be concerned that the temperature only reaches 130 degrees? I ran the engine for about 45 minutes under load out of the marina and back to test hoses, valves, pump, etc. for leaks. Never got above 130 degrees. Should I replace the thermostat? The temp sending unit should be fine as it showed high temps when the problem started.
So now I have a new, related question. Now that the engine is cooling properly, should I be concerned that the temperature only reaches 130 degrees? I ran the engine for about 45 minutes under load out of the marina and back to test hoses, valves, pump, etc. for leaks. Never got above 130 degrees. Should I replace the thermostat? The temp sending unit should be fine as it showed high temps when the problem started.
I wish I had a definitive answer. Everything seemed okay as I disassembled and/or replaced things. I think it was likely the gap between the impeller and the worn inside surface of the cover plate. However, I am not sure. The pump is simple, so there aren't many places for it to fail. There is also the (remote) possibility that more than one impeller was faulty. I tried 3 new ones during the ordeal.