Sea Water Pump not pumping!

[Kenny C]

This is for a 1982 Universal M-30 with a Oberdorfer Raw Water Pump.

Last weekend started the engine and noticed no water pumping out the exhaust. Pulled the impeller cover plate off and sure enough the impeller was toast with no water what so ever in the impeller housing. Ordered a new impeller and gasket and installed yesterday. Still no water being pulled through the impeller housing. Started pulling lines off and checking for obstructions, everything clear. Pulled the impeller cover plate off to check if the impeller shaft spun when the engine cranks, spinning like a top. I filled the impeller housing with water to try and prime the pump still nothing. Applyed suction to downstream side of pump and was able to pull water through that way so i have water to the pump for sure.

Note: i did notice that water was dripping from the impeller shaft when i had water in the housing.

Here's where i'm stumped, how can the impeller be spinning but not pulling any water? Would the leaking impeller shaft be introducing that much air in the system as to keep it from creating suction?

Any advise would be greatly appreciated.

 

[RichH]

Two things possible
1. the Oberdorfer type vane pumps have a removable 'cam' surface which causes the impeller blades to compress/bend. If the 'cam' also came out with the impeller and was lost the impeller will not function properly ... and you will see a teeny ~3/32 'hole' on inner horizontal surface of the pump body where the 'cam' mates with pump body if the cam is now missing.
2. The Oberdorfer type pumps depend on a specific 'clearance' (~0.001") between the side walls and cover plate and the impeller sides to 'seal' (with water). If you applied a THICK replacement gasket to the cover plate or you see a large amount of abrasion wear on the inside of the cover plate, etc. ... leakage internal to the pump and little to no flow due to water 'leaking' past the SIDES of the vanes.

if you need: http://www.oberdorfer-pumps.com for parts lists, diagrams/sketches & parts lists, etc.

 

[kloudie1]

Had a similar problem on a friend's Catalina 34.. For the rreplacement impeller, he'd bought the "blue" one that talks about being able to be run dry. What we found was that the blue impeller for the Oberdorfer was a smidgen smaller in diameter and a smidgen thinner.. We could get it to pump by pulling water through it then starting the engine.. It would pump fine .. but when shut down for 30 minutes or more, it would un-prime ..We changed the hoses on the suction and discharge side of the pump and the problem was better but it still needed priming to begin pumping. We changed the seal and that helped ... then after all that, went back to the original black impeller and it has been working fine for a couple of years now.. Check hoses, hose clamps (you won't see water leaking out of the small cracks, but air may be leaking in).. HAve the pump seal changed and check the bushing while in there.. This problem is well discussed on the Catalina 34 forum..

 

[Stu Jackson]

To add: make sure the inside of the faceplate is smooth. If not, sand it down or buy a new one.

 

[Kenny C]

Thanks for the info. I did get the orignal black impeller so thats not an issue. The faceplate didn't appear to be scored too bad (but i'll re-check that), The cam is still installed and I used the thin repleacement gasket that was exactly like the one that came off it. I did notice that the shaft lock ring shown on the Oberdorfer documentation was not installed, could that be an issue with side play on the impeller?

Also after looking at the Oberdorfer site it doesn't appear that the right pump is even installed. With an M-30 engine i'm supposed to have a Pump Number N202M-15. According to the info i'm seeing it appears that i have a Pump P/N N202M-03 or N202M-07 installed. Got to love it!

 

[Ron20324]

And the thru-hull is not clogged? Maybe there is a strainer you overlooked? Just thinkin'.

 

[onecoolair]

This is for a 1982 Universal M-30 with a Oberdorfer Raw Water Pump.

Last weekend started the engine and noticed no water pumping out the exhaust. Pulled the impeller cover plate off and sure enough the impeller was toast with no water what so ever in the impeller housing. Ordered a new impeller and gasket and installed yesterday. Still no water being pulled through the impeller housing. Started pulling lines off and checking for obstructions, everything clear. Pulled the impeller cover plate off to check if the impeller shaft spun when the engine cranks, spinning like a top. I filled the impeller housing with water to try and prime the pump still nothing. Applyed suction to downstream side of pump and was able to pull water through that way so i have water to the pump for sure.

Note: i did notice that water was dripping from the impeller shaft when i had water in the housing.

Here's where i'm stumped, how can the impeller be spinning but not pulling any water? Would the leaking impeller shaft be introducing that much air in the system as to keep it from creating suction?

Any advise would be greatly appreciated.

Try back flushing your raw water heat exchanger. Look for what's left of your impeller in there. Also take the time to clean out any build up of crud inside engine heat exchanger too.

 

[Kenny C]

Update: The pump installed is not the N202M-15 as called out in the Oberdorfer documentation but rather the N202M-03 that has been converted to fit this engine. After talking to the guys at Oberdofer this should not be a ploblem especially as it has run like this for who knows how many years.

So now back to the orginal problem. I removed the downstrean (engine side) hose to eliminate the heat exchanger and associated plumbing and the pump is still not drawing water. Next question: Is there a special trick for re-priming the pump? This setup does not have a water strainer installed but rather a straight hose from the thru hull to the pump. (Like i said earlier i do have good water flow from the thru hull to the pump.)

I did go ahead and order new seals and a new shaft and will install them this weekend but i'm having a hard time believing that the water seepage i'm seeing around the shaft would completly shut down the pump suction. What in the heck am i missing?

 

[Delezynski]

Saw this SAME thing take place a couple of times. Each time it was traced down to the face plate gasket. More often than not, it is two of them in place, or that the face does not seat properly. ANY THING that increases the side clearance of that impeller render the pump useless.

Hope you find the problem!

Greg

 

[Stu Jackson]

What in the heck am i missing?

Greg gave you a good idea. Have you done EVERYTHING that was suggested?

 

[Kenny C]

Update: Replaced the 2 seals, installed new shaft, re-faced the faceplate. Water Pump Pumps! Thanks to everybody for putting up with my frustration. Between here and the Catalinas website there is a wealth of knowledge and I greatly appreciate it. Now, if i can just get someone to come down here and get in the water to remove the dockline that i ran over thats tangled up in my prop everything would be all right.

 

[Glenn17467]

start at the thru hull, pull hose and open thru hull. Should get a stream of water. Next, take hose off at raw water strainer, open thru hull. Has the strainer been cleaned?

Another point of blockage, though it does not seem to be your problem since you are in a inland lake. Others could find this useful. The inlet to the HX can get blocked with salt build up and create back pressure from the raw water pump. I had this problem and eventually had water in the crank case. Now I pull the inlet hose off the HX and clean out the inlet, you cannot see in it w/o a mirror. I do this every couple of months.