Oberdorfer water pump problem

[BlindAmbition]

Hi everyone. I replaced my Sherweood raw waterpump on my M25XP a few weeks ago. Note for anyone doing that, it sits different and the brass fittings coming out of the pump and the existing hoses have to be altered somewhat. So pick up a straigh fitting and some longer lengths of replacement hose.

Anyhow, my old pump was weeping, although the engine was running at proper temp (165).  After the replacement I ran the engine a while and all seemed normal and I was getting water flow out the stern. I took the boat out a week or so later and it ran warm (180 in short order) - there appeared to be water flow out the stern, but seemed possibly light. Today I removed the impeller and checked everything out. All seemed kosher. Upon start of the engine I got no water flow out the stern. Next steps???

[mark_53]

Easy stuff first. If water temp is high, your engine temp will be high too.
Check if your through hull is open and the sea strainer clean. Check if the through hull is not blocked. To do this, remove the hose from the through hull. Then open it. If water gushed out its clean. If not, shove a piece of 14 gauge romex wire down it to clear.

[KWKloeber]

Negatory on the Oberdorfer pump aligning any different than the Sherwood, nor needing any different hose barbs.  All that's needed is a very slight mod to the base (w/ a Dremel or even a file) and a very slight mod to the hose elbows (again Dremel or flat file.)  See the TechWiki article "Replacing a Sherwood Water Pump with an Oberdorfer" -- which shows it all.

As to overheating, could be a few issues -- as Mark said check for sea water flow, obstructions in the hoses, obstrustructions in the heat exchanger (scale, weeds, or old pump impeller parts in the tubes,) and an obstruction in the muffler injection elbow (some have found it virtually blocked off with scale.)

-kk

[SPembleton]

In addition, I had a situation where i replaced my impeller when i was on the hard and forgot to shut off the raw water intake. The water ran out of the pump. When i replaced the impeller, launched and started the engine, i had no water coming out. I had to close the raw water intake, pour some water into the output side of the pump, replace the output line, open the raw water shut off and everything was fine.

[Ken Juul]

I think Steve meant pour water into the hose between the pump and the thru hull to ensure there isn't an air block.

[Stu Jackson]

The pump is just below the waterline and shouldn't need to be primed, but others have suggested it.  The one time mine didn't work was a clogged intake seacock.  I took the hose off the pump to the seacock and stuck the dinghy foot pump on it and blasted away.   That's a lot easier than reaming the seacock with a dowel, since the layout of my raw water strainer precludes that.  Some have replumbed to put a T there to allow it to be done more easily.

[Ron Hill]

Blind : I sounds to me like the sudden increase in engine temperature is unrelated to the change of one pump to another - especially on an M25XP engine!!

Are you sure that there isn't a kink, neck down or obstruction in the raw water lines? into the pump or the HX??

A thought, 

[SPembleton]

I think Steve meant pour water into the hose between the pump and the thru hull to ensure there isn't an air block.

Actually i did describe it right.  I poured water into the output side of the pump.  That way the pump body filled with water.  It started working immediately and hasnt given me any trouble since.

[britinusa]

We had an overheating issue in Biscayne Bay (grass sucked into the thru hull). I cleared it by disconnecting the Raw Water Strainer from the Thru Hull, and connecting it to another thru hull.

During that process, AFAIR, water drained from the raw water strainer, which would suggest that there was a possible loss of prime. And I would guess (rightly/wrongly?) that the pump self primed as I did not fill the hoses to try and prime it.

[Ken Juul]

Thanks for the clearification Steve.  I don't worry about filling the pump cavity, if the inlet hose is full water will be in the pump in a matter of seconds.  Yes, it should self prime, but why take the chance of ruining an expensive impellor if it doesn't?

[patrice]

Hi,

When I change the pump impeler, I rub it with soap dishes.
It lubricate it for the time required to get water inside the pump.

[KWKloeber]

Though our pump sits further below WL, the C-30s sometimes (rarely) experience this issue.  Sometimes the pump loses prime when heeled (and gets an airlock -- our seawater thru hull sits somewhat off to port.)  The easiest way may be, and what we usually do, is simply loosen the pump cover screws (no need to remove them or the cover) until water flows out.  If it doesn't, then investigate further -- screen or thru hull blocked, etc.

If this were a recurring issue, I would install a tee and quarter turn valve in the line to remove the air lock.  I have seen photos of some installing a "Prestone" auto coolant flush tee (with the plastic garden hose threaded cap) in the line.  DON'T even THINK about doing that.

FYI

There are knurled "thumb screw" cover screws available that you can replace the Phillips screws. 

ALSO - remove the deep six the cir-clip on the pump shaft -- it has no function and makes it more difficult to change the impeller in an emergency (or anytime else for that matter.)  If you have an old style (202M-) pump, there is an aftermarket o-ring style cover available (instead of the paper gasket cover.)  The new style (N202M-) pump covers DO NOT fit the old style (202M-) pumps.

-kk

[Lance Jones]

I recently had a similar issue. My steps:
1) You've done many of them already.
2) (New ideas) Make sure your coolant level is full. Mine was a wee bit low.
3) Also, this might be a good time to replace your thermostat. At least tap it when it starts getting over the 165 - 170 degree range.