Rebuilt Oberdorfer raw water pump and now engine temp rises with RPMs

[pablosgirl]

All,

I finally got around to rebuilding my Oberdorfer raw water pump using Ron's excellent article in the May 2002 Mainsheet.  The pump no longer leaks, but now I find that the engine heats up when the RPMs are over 2K.  So at 2500 RPM, temp 180 and at 3000 RPM, temp 200.  Before the rebuild always a solid 160.  The old impeller was intact, so there are no impeller bits in the HX.  The only thing that I can think of is that I reversed the hoses on the pump body.  Can anyone tell me the proper water path?  Does the thru hull hose go to the left or right pump nipple?   After some searching on the web site I found that the pump impeller rotates clock wise (thanks Stu!).  With a clockwise rotation, I would think the right pump nipple.  I do not remember which nipple I installed the thru hull hose to now.  Any other thoughts?

Thanks,
Paul Shields

[SeaFever]

Paul,

A quick check would be to see if you are getting water coming out of the exhaust while the engine is running. If you are, then the hoses are connected correctly. If not, or very little, switch them and check.

[Ken Juul]

According to the OEM spec sheet the rotation of the impellor determines the in and out ports.  Having your hoses reversed would severely restrict water flow, giving you your overheat condition.

[Stu Jackson]

Paul, if you are getting the right amount of water thru the muffler and out the transom, then the next step is to check the faceplate and the thin paper gasket.  Did you get a new faceplate when you rebuilt the pump or just the seals and carbon bushing?  I once had an engine water problem, fixed it and then just as I was starting to pull my hair out, checked the faceplate and realized it was scored.  Got a new faceplate and all was well.

[SeaFever]

Hi Paul,

I agree with Stu, you could have problems if you have scoring on your face plate. However, you seem to have a more 'severe' issue than that could be caused by scoring. Also given that you recently rebuilt it I am assuming you would have noticed scoring on the face plate if there was some. Clearly as noticed by you, you may have a simple issue of crossed hoses. Ken has provided the correct comment that the water flow in the water pump depends on the direction of rotation. Since you know the direction of rotation of your pump (or can check that pretty easily). Here is a generic explanation that may help.

As always a picture is worth a thousand words. Attached is a picture of a water pump shell I stole from Main Sail's website for illustration. In this case if the impeller is rotating clockwise the nipple on the right would be input. If the impeller was rotating anticlockwise (as seen from the front of the picture) the nipple on the left would be the input. Basically, depending on the direction of rotation, the nipple that precedes a longer traversal for the water before reaching the next nipple, would be the input. This allows the impeller to collect a volume of water before shoving it into the HE.

I am sure Stu and Ken will chime in if my explanation is incorrect. Although this picture is not that of an Oberdorfer pump that you have, I hope this helps you determine your input nipple. Cheers.

[Tom Glennon]

I just installed a new Oberdorfer pump... has the nipples on the lower left as you face the engine, not across like the picture of the pump shown here... it had 5 mounting holes and the face plate has 4 screws holding the plate ....

[pablosgirl]

Stu,

I am getting water out the exhaust port at the transom and it does increase with RPMs, but I am not sure what the "right" amount of flow would be?  How much water should I see at say 2500 RPMs?  The odd part of this whole experience is that when I disassembled the pump, I found the face plate severely scored.  I mean to the point the there was a circular grove in it from the impeller hub and you could see where the impeller blades had scored a circular "donut" into the face plate.  And the dam thing worked great!  Like I said earlier, I never say above 160 even at 3000 RPM for 30 miles on a trip just last month.  I also had to replace the shaft because a grove was worn where the water seal contacted the shaft.  This was probably the source of my water leak.  The shaft still fit tight in the carbon bearing so I did not replace the bearing.  I resurfaced the face plate my self using wet/dry sand paper and starting with 100 grit then to 220, then 400, then finished it off with 1000 for a nearly mirror smooth finish.  Took a couple of hours one evening, but is always more fun to do boat stuff than watch TV!  The face plate is a little thinner now, but that should not matter as long as it is smooth. 

SeaFever, I had the same theory on pump operation as you.  I was hoping that Stu or Ron would confirm that the right pump nipple connects to the thru hull fitting, given that Stu's earlier finding that the impeller rotates clockwise.  I plan to go down to the boat tomorrow and check which hose is where and hopefull need to swap them as this will answer this question.  I'll let you know what I find.

Thanks,

Paul Shields

[SeaFever]

Tom,

You missed the following text from my last para.."Although this picture is not that of an Oberdorfer pump that you have, I hope this helps you determine your input nipple"....

[lucky]

pablosgirl
I have a oberdorf pump on my 1986 c34.As you look at the pump from the front of the engine the bottom nipple hose goes to the HE the top nipple hose gets water from the seacock.
Al
Lucky #13
c34

[Ron Hill]

Paul : Had a lengthy reply that went out into cyber space somewhere!
 
If you are looking at your pump from the front, the bottom nipple (approx "7"o'clock) is for the exhaust and the top nipple (approx "8/9" o'clock) is the inlet.

It almost sounds like the brass insert in the impeller is not solidly attached to the rest of the rubber impeller.  Try a differant impeller. 
And/Or make sure that the stainless shaft is firmly inserted in the cam slot in the engine.   Hope this helps

[pablosgirl]

Ron,

I got out of work a little early today and went by the boat on the way home to check the hoses.  It looks like I connected them correctly.  So it has to be either the impeller or the face plate.  I will try swapping in the old impeller next to see if that improves things.  Thanks for all the advice/info.

Paul Shields

[Ron Hill]

Paul : Also look at the way you attached the face plate!!  
There are 4 bolts(screw heads) 2 are shorter than the 2 longer - check the holes that they are going into!!  They are short and long for a reason!  A thought

[pablosgirl]

Ron,

OK, I checked my bolts and indeed two of them are just slightly longer.  So I did not pay attention which ones came from which hole originally.  Can you tell me which holes get the longer screws?  I have taken the face plate off to polish it some more and will put the screws back where you tell me.  If that does not solve the problem I will swap in the old impeller and give that a try.  I wonder if anyone else has had problems with the DEPCO impeller kit?

Thanks,
Paul Shields

[dgill]

One other thing you may check is whether your engine box insulation might be intermittantly touching the sending unit on the front of the thermostat housing.  I had this issue and indeed when the throttle was increased the water temperature increased on the gauge.  I put at piece of rubber over the wire/nut and the problem disappeared. 

[Stu Jackson]

Can you tell me which holes get the longer screws? 

Paul, one would believe the deeper holes.