Life expectancy of a raw water pump

[pablosgirl]

I have what I think is the original Oberdorfer 202M-15 raw water pump on my m25XP engine.  I replaced the shaft and lip seals 3 1/2 years ago and have replaced the impeller every season with one ordered from Depco.  We use the boat year round and a few weeks ago I noticed that the amount of water coming out the transom was not what it should be, so I ordered a replacement impeller.  I replaced the impeller and the flow rate did not improve.  I investigated further and found a stick loged in the thru hull removed it with a long screw driver after taking off the raw water hose.  Put it all back together and much to my suprise the water flow did not improve.  Took of the pump cover plate and polished it's surface and reinstalled.  Still very low water flow.  Took all the raw water hoses off and verified that they were clear.  Took off the heat exchanger end cap and rodded out the tub sheet with a coat hanger.  Still low water flow.  I even ran the engine with the end cap off the heat exchanger to observer the output of just the pump and low water flow.  Thinking that I had toasted the new impeller, I purchased another and installed it.  Still very low water flow.  So I am thinking that the pump body is so worn that I am not getting a good seal on the back face of the impeller.  Is there any way to recondition these surfaces or am I destin to purchase a new pump?  What is the useful fife of these pumps? 3000 hours?

[Stu Jackson]

Paul,

1.  Have you refinished the faceplate?  That's usually where the drop off occurs.  Either fine sand it down or buy a new one.

2.  Longevity:  We replaced the Oberdorfer we had when we bought the boat at around 900 hours.  I did this because I didn't want to pay almost as much to have the shop redo the seals as for a new pump.  This is pretty much what a lot of new-to-them owners do.  Then I got smart and read Ron Hill's excellent writeup of how to replace the seals, and did it myself, for all of the $10 for the seals and a few hours of work.  http://c34.org/bbs/index.php/topic,6766.0.html  2,501 engine hours.

[pablosgirl]

Hi Stu,

1. Yes, I sand/polish the face plate each season when I replace the impeller.  It is so smooth, it has a mirror finish.  I might try taking a wooden dowl and wrap it with sand paper to do the sides and back of the pump cavity to see if that makes any difference.

2. Yes Ron did an excelent job on the lip seal replacement write up.  It is what I used to do mine.

[Ron Hill]

Paul : Before I sprang for a new pump, here's what I'd try first:
1. change the inlet hose from the thru hull to the pump
2. change the exhaust hose from the pump to the HX.  Look (CLOSELY) at the exhaust elbow on the pump to that hose and make sure it is clear!!

Don't know if these are original hoses or not?, but I'd change them.  The inlet hose needs to be a wire reinforced because it's on the suction side and the exhaust hose can be a nylon reinforced because it's on the pressure side.

A few thoughts, good luck

[lazybone]

The most important question is;  What is your engine temperature?

If your temp is good then you just might be chasing windmills.

[pablosgirl]

Hi Ron,

I replace all the raw water hoses 3 years ago with reinforced hose when I replaced the lip seals in the raw water pump.  Also, I have removed both of the water pump hoses and held one end of each hose to the end of a water hose and got full flow.  I ran SS rigging wire through the pump elbows to make sure that they were clear. I installed my temp/emergancy electric raw water pump and got plenty of water throgh to the transom with the engine staying at a rock solid 160 degrees through all RPM ranges.  So the problem is definitly in the pump.   I can't think of anything else to try but another pump body.

Lazybones,

The flow is really low.  It pushes a cup full about once a minuet at 2000 RPM and much less at idle.  The temp ran at 185, but the water temp was 55 degrees.  It definatly won't work in 85 degree water we have in the summer.  If I increase the RPMs above 2000 the temp rises.

[Ken Juul]

My guess is the heat exchanger is partially blocked.  Run the engine with the raw water pump exhaust hose in a bucket and see how much flow you get.  If it looks normal then the pump is not the problem.  Might also be an intake blockage, rather than the screwdriver try cleaning the thru hull with a piece of dowel, can't remember the size, but it is here on the forum in one of Ron's posts. 

In my experience, overheating is normally a HX problem.

[Ron Hill]

Ken & Paul : The size of the wooden dowel to clean a stopped engine intake thru hull is 3/8".

If your temp remains at 160F with very little coming out of the exhaust then you have two problems:

1. There is a stoppage somewhere in exhaust water from the raw water pump.  If the raw water pump will pump a bunch of water into a bucket, if the elbow is clear and a new hose to the HX, then check the water output of the HX, the hose to and the anti syphon valve and the water output from the anti syphon that goes into the exhaust riser. 
The muffler should be OK as it's two simple 1 1/2" PVC pipes so the blockage should be before the muffler.
2. Little water and a steady temp of 160F then you'd better check the temp sender that's screwed in to the thermostat housing!

Good luck

[Stu Jackson]

I have been "relentlessly" suggesting for the past 14 years of our 15 year C34 ownership that skippers REMOVE their HXs, because the inlet port of the HX from the rw pump gets full of salt, if you're in saltwater, it simply drops out there because it's the first place the hot hits the cold.

If you're in fresh water, it can't hurt either, who knows what's in your water? 

[Indian Falls]

2 things:  if you sand and polish the plate everytime you service the impellor maybe you've take off too much material by now. 

Second: what RPM are you checking your flow at? A very small RPM change is a big change in water output at low idle. It may be possible to find some data concerning GPM at a given RPM and then you can rest easy. 

[pablosgirl]

Hi All,

There seems to be some confusion on what I tried and have not tried.  So let me try again.
1) Symptom: very little water flow at 2000 RPM. Maybe 1 8oz cup every minuet.  I would normally get 15 times that amount at this RPM.  I get even less at idle.  Engine temp at 185 deg with 55 deg bay water at 2000 RPM, any increase in RPM pushed engine temp higher.

2) replaced impeller and gasket with Depco kit.  Still little water flow.

3) Went into trouble shooting mode.

3a) took raw water inlet hose off thru hull and found very little water flow.  Took, long screw driver and pushed out blockage.  Now get full flow as in this could sink the boat flow if let run.  Thought, eureka this is the problem!  But flow out transom still as before, too little.

3b)  Next the HX.  Took off the end cap where both the raw water lines attach.  Found salt deposits partially blocking tubes.  Took coat hanger and roded out each of the tubes.  Ran engine with end cap off of HX and still very little water flow.  So problem must be between HX and raw rater thru hull.

3c) Next took off both raw water hoses and used dock side water hose to "flush" out both hoses.  Water flowed through hoses at same rate as dockside water hose, so no blockage there.  Found a blockage in the inlet raw water pump elbow and cleared that.  Ran engine again and still very little water flow.  Conclusion, must be poor seal inside pump body.

3d) Thinking that I "toasted" the new impeller I had put in due to the low water flow issue.  I put in another new impeller and ran the engine AND still very little water flow.  Conclusion the other surfaces (back and sides) in the pump must not be making a good seal.

4) to confirm this I took out my trusty emergency raw water pump and put it in place of the engine driven water pump.  Ran engine and had near normal water flow.  The emergency pump is a Rule 500 GPH live well bait pump that runs on 12v.  Every one should have one in their spares kit.  I once motored over three hours at 2500 RPMs with this pump and it got us home after the raw water impeller quit pumping.  The impeller did not loose any vanes, just quite pumping water that time.

So as I have previously stated.  I sand the cover plate side that contacts the front face of the impeller to remove the groves that the impeller wears into the face plate.  I use a series of sand paper ending in a 1500 grit that puts a mirror finish on the cover plate.  Ron, recommends this in his article, except I think he recommends taking it to a machine shop.  The brass is soft enough that sand paper will true up the surface to provide a good seal against the impeller.  This does not alter the clearance aspect of the pump, but I suspect the the impeller is also wearing down the back surface.

The question is....  Can you polish the sides and the back surface of the pump body as you do the front cover plate or is the pump shot and needs replacing?

I hope this clears up this discussion.

[Indian Falls]

yep sorry I did miss a few of your details...

What about air?  Is your pump getting/sucking air from somewhere between the housing gasket and the through hull?  The water line is below the pump I think, someone else can clarify that. 

Mine pumps what you describe when I get a lot of air in the hoses.  Since that time I always fill the hose with water and reattach to the sea cock.  I also use vaseline on the impellor at install.  Once I used Neosporin cuz I had nothing else.  I think it helps the dry impellor get rid of air better, not to mention lubrication until the water reaches it.

Is the cam nice and flush with the housing face?  Another place for air to get around the fingers.

Can you measure the width of your impellor with a dial or digital caliper?  Is there a possibility they are just a bit too narrow?  I have two spares I can measure for comparison,  both are the standard Sherwood rubber type.

The oring in the depco kit wouldn't happen to be just a bit bigger cross section than what usually goes in there?
Meaning that something is keeping the housing from squeezing the impellor up against the plate.  (seen that on a different pump just last month)