replacing the Oberdorfer salt water pump impeller on the universal M25
December 8, 2011pretty much right out of the Owners Manual, but with pictures
Oberdorfer 202 M-15 (4 screws), Impeller: OBE 6593 (replaces Universal/Oberdorfer 295628)
I admit it, I had my doubts. Sometimes it seems like every boat project has a hidden gotcha - but changing the impeller wasn't one of them, in fact it was so easy this is now my favorite diesel maintenance task on the boat!
How to change the impeller in the Oberdorfer 202 M-15 salt water pump
- Buy the impeller, the gasket, and glycerin for lubrication
- Oberdorfer 202 M15 impeller part # OBE 6493 - $30.22, San Diego Marine Exchange
- impeller gasket part # OBE 6599 - $5.95, San Diego Marine Exchange
- glycerin - $5.61, Rite Aid pharmacy
- optional (if yours is missing) - Snap Ring part #5373, San Diego Marine Exchange
- Have some paper towels or rags on hand to mop up any sea water spillage when you take the cover off of the Oberdorfer pump
- Close the raw water intake valve.
- Unscrew the 4 screws on the cover of the Oberdorfer 202 M-15 pump
- Tap cover on side to loosen, being careful not to damage the cover mating surfaces (oops, missed this part! Oh well, the cover came off easily)
- Remove the cover
- the 2 top screws are shorter than the 2 bottom screws.
The last time the impeller was replaced was Sept 2006 - 183 engine hours ago. A lot of salt water calcification gunk around the cover plate
- Remove the snap ring
- Snap ring? What snap ring? I thought there wasn't a hidden gotcha on this project! The manual calls out a snap ring on the end of the shaft in the center of the impeller - there wasn't one.
- There WAS a washer on the back of the impeller - not a snap ring. The Universal M25 parts manual doesn't show a washer, but an updated parts data sheet from Oberdorfer shows both a snap ring on the front and a washer on the back of the impeller.
- Hold the shaft in place with a screwdriver to keep it from sliding forward and gently pull/pry the impeller off the shaft with another small screwdriver. I'll probably use needle-nose pliers for this next time.
- Remove any traces of the old gasket and clean up the surface.
- Clean out the calcification build-up inside the pump body.
- Clean up the inside of the cover plate - a green Scotch-Brite scouring pad works great for this
- Lube up the new impeller with the glycerin and put the impeller on the
shaft. There's only one way to do this because of the notch on the shaft and
impeller. It was easy to orient the blades to the correct rotation, where the
blades are squished by the shoe they have to go some direction - might as well
be the right one. The rotation on the 202 M-15 is counter-clockwise (reference the pics and the
Oberdorfer 202M series data sheet.)
My Oberdorfer 202 M-15 doesn't have a grease cup, it has a carbon bearing that the shaft slides into, so other than the impeller, cover and body there's nothing else to lube.
- Lube the inside of the cover with glycerin, put the gasket on and put it back on the pump.
- Tighten the cover screws evenly.
- Open the sea water inlet valve and check for leaks.
- No leaks? Start the engine, check for sea water coming out the back. Check the temperature.
EASY! And a good thing it is, because I'll be doing it again soon - thought to call Oberdorfer Tech Support about the washer I found at the back of the impeller. The washer is there to help with wear and, because I didn't see it on the part callouts in the Part Manual, I put it on the front of the impeller. The Oberdorfer advisor said this shouldn't cause a problem because the impeller has indents at the front and back. The updated parts data sheet from Oberdorfer for the 202M series shows both the washer and spring clip.
From page 32-33 in the Universal M25 Owners Manual
SEA WATER PUMP:
Your engine is equipped with a rubber impeller type sea water pump.
CAUTION: DO NOT RUN PUMP DRY AT ANY TIME OR YOU WILL DAMAGE THE IMPELLER, CAUSING ENGINE TO OVERHEAT.
You can use methyl alcohol based anti-freeze compounds such as Zerex, Shell Zone, Pyro Permanent, Permagard and Dowgard.
REPLACEMENT OF SEA WATER PUMP IMPELLER:
- Be sure engine is stopped. Turn off sea water inlet valve.
- Loosen and remove the pump cover screws.
- Tap cover on side to loosen, being careful not to damage cover gasket and remove cover.
- At this time, be careful not to pull the pump shaft forward or out of its present position. If the shaft does come forward during the changing of impeller, it will be necessary to remove complete pump.
- Remove the snap ring located on the end of shaft in center of impeller, with shaft held in place.
- The impeller can now be pulled off the pump shaft. Be sure to hold shaft in place with a screwdriver or etc., when removing the impeller.
- Replace with the new impeller by rotating. (You can lubricate impeller with vasoline or oil prior to installing.) This will also prevent burning of new impeller when first starting engine.
- Replace snap ring, being sure it is in the groove all the way around.
- Replace gasket and cover (oil inside of cover).
- Replace the cover screws and tighten evenly.
- Open sea water inlet valve, check for leaks.
- Engine can now be started, check engine temperature.
NOTE: IF DURING IMPELLER REPLACEMENT THE PUMP SHAFT CAME FORWARD, IT COULD HAVE COME OUT OF THE GROOVE AND DRIVE ADAPTOR. IF SO, YOU MUST COMPLETE THE FOLLOWING.
- Loosen and remove the two capscrews holding the pump body to engine.
- Slowly move pump away from engine as the adaptor will come out.
- Complete the replacement of impeller as noted above.
- The pump shaft will now be protruding through the body mounting flange.
- Place the adaptor on to the pump shaft aligning the pin on the groove.
- Align the slot on the other side of adaptor with the drive shaft in engine and place pump on engine.
- Hold in place and start the two mounting capscrews. TIGHTEN FINGER TIGHT SO PUMP IS FREE TO MOVE AND ALIGN ITSELF.
- Open sea water valve and start engine at idle. This will align pump to the drive and adaptor.
- Now tighten capscrews carefully while engine is running. CAUTION: BE VERY CAREFUL DUE TO V-BELT MOVING ON FRONT OF ENGINE.
- Feel the bearings to make sure they are not hot; they are located in the center of pump body.
NOTE: THERE ARE TWO TYPES OF SEA WATER-RUBBER IMPELLER PUMPS USED. ORBERDORFER PUMP HAS 4 SCREWS SECURING COVER TO PUMP BODY AND SHERWOOD PUMP WHICH HAS 6 SCREWS SECURING COVER TO PUMP BODY. NOTE WHICH PUMP YOU HAVE ON COVER OF THIS MANUAL. IT IS RECOMMENDED TO HAVE A SPARE IMPELLER AND COVER GASKET ON BOARD AT ALL TIMES.
ORBERDORFER IMPELLER NO. 295628 - COVER GASKET NO. 295626
SHERWOOD IMPELLER NO. 287439 - COVER GASKET NO. 295745
CAUTION: DO NOT RUN PUMPS DRY OR WITH SEA INLET VALVE CLOSED. LACK OF WATER WILL CAUSE EXCESSIVE HEAT BUILD UP DAMAGING OR DESTROYING THE RUBBER IMPELLER, AND ENGINE WILL OVERHEAT.
IF VANES COME OFF IMPELLER THEY MUST BE LOCATED AND REMOVED TO INSURE THEY ARE NOT BLOCKING OR RESTRICTING THE COOLING WATER FLOW IN THE ENGINE, HOSES, OR FITTINGS.