Saturday, April 20, 2013

Revenge of the Onan MDJE Generator

I've told you before that I can be a real dummy.  I just don't know where my head is sometimes.  Let me give you an example.  Yesterday, I was looking for my cell phone and couldn't find it.  In my search, I found Pam's.   So I used her's to call mine, quickly locating it under a magazine where it crawled to hide.   I put Pam's back, flipped open mine (yes, I'm that antiquated) and saw that I had a missed call from Pam.

"Huh", I thought.  "I wonder what she's calling about?"

It only took about five seconds.   But duh.

Concerning the generator overheating problem, I have decided that the problem can't be on the freshwater side.  Everything there has been cleaned, tested, flushed, and otherwise deemed to be in good working order.  But how can the problem be on the raw water side?  It seemed implausible because the raw water pump spews water like crazy.  My friend Dick, who is mechanically inclined and savvy, along with several readers, suggested I check the raw water impeller.  Maybe it's just not moving enough water.

OK.  Whatever.  Looks fine to me.

I removed the raw water pump cover.

Where did the impeller go?  Maybe it's behind that black gunky looking thing.  I pulled the pieces out, one by one.  Sadly, that is the impeller.  Happily, I had all six vanes, although small pieces were missing.  

I looked on the pump.  No identifying numbers anywhere.  Nothing.  I looked in my Onan Parts Bible.  Not even anything in there.  I measured the impeller shaft and the diameter and depth of the pump body, and hied myself over to West Marine where they had an impeller of the right dimensions.  I skipped happily back to Drift Away where I carefully compared the old impeller (what was left of it) and the new one.  It all looked good, until I saw the set screw in the new package.  The old one didn't have a set screw.  I looked at it with a magnifying glass and saw a small flat.  The shaft on the pump is D shaped, and the new impeller used a set screw.  It wouldn't work.

For my landlubber friends, this is the thing about the marine industry that makes us boaters insane.  You would think that there would be some standards and uniformity to boat parts, but no.  If that was the case, you could probably pay $5 for this rubber part instead of $66.

So back to West Marine, where a nice young associate returned the one I bought and ordered the correct one for me.  It will be in next Friday.  Meanwhile, I'll try to hunt one down locally or over the internet.  It wouldn't hurt to have a spare.

Just to finish up, I took my specially set up hose and flushed out the seawater intake line, as well as the one running from the pump to the heat exchanger.  All was good.

Early in this project, I had removed the fitting on top of the expansion tank that the radiator cap attaches to.  I did this to feel for the thermostat inside the expansion tank.   There was a 33 year old gasket under there that sort of disintegrated and it was now leaking.  I removed the fitting and sealed it up with Form-A-Gasket.  It's great stuff.  Put a tube in your outfitting kit.

So I'm at a standstill until next week, but I'm pretty confident that the impeller is the problem.   How that little nub of the old impeller moved so much water is beyond me, but I think this is it.  At least I hope so.  There's really nothing else left to do besides an exorcism.


  1. I have been able to get raw water impeller's at NAPA auto parts.

    Bill Kelleher

  2. That Impeller wasn't pump'n noth'n-- All you see is exhaust bubbles....

    I take my impellers out for the winter layup so they don't get a set to them-- That way I also can inspect them at the same time....

    It defiantly didn't hurt to clean the heat exchanger!!

  3. Dave;

    Here is a very good place to get all sorts of tips on home-building.