Tuesday, April 16, 2013

Tackling the Onan MDJE 7 1/2 KW Generator

I've been showing Drift Away to both real prospective buyers and many dreamers lately.  The subject of why Drift Away has two generators comes up every time.   My answer is that I don't know for sure.  But this is what I suspect.

I think Drift Away came from the factory with only the 15 KW generator.  I'm surmising this because it looks like the engine room control panel was modified to add the 7 1/2 KW generator.   Why did the first owner add another generator?

Well, diesel engines like to be run under load.  I've been told by several savvy mechanics that this is very important.  Running the big 15 KW to brew a pot of coffee isn't really much of a load.  So I'm guessing that the original owner (Mr. Tiner, who follows our blog, so maybe he'll comment here) added the small generator for light loads, and saved the big 15 KW for when all the A/C units were running, TVs were being watched, and dinner was being prepared.

The 15 KW has start controls in the helm station, and so I remember to start that one every few months.  I hadn't started the 7 1/2 KW since Norwalk almost two years ago.  Since the boat is for sale, I thought I should make sure everything was OK with it.  So I crawled over the starboard side Ford Lehman a few days ago and cranked it.  I cranked just fine, but didn't fire up.  Nuts.

I mentioned in a previous blog that I had redone the fuel lines on the engines a year and a half ago and that possibly I messed something up.  I pulled up the floor panel to take a look...

and decided to postpone sorting this out for another day.  That day came.

I needed to pull the soundproofing off the generator so I could trace the fuel lines.

I unloaded the stuff sitting on top of the generator and opened the cover.

I followed the fuel lines from the engine.  One, the return line, was tee'd to the starboard Ford Lehman's return line.  The other, presumably the fuel feed, vanished under the floor.  Rats.

I like to label things.  I saw where I labled the preheat and start/stop switch two years ago.  Why not just give it another go?  I held the preheat switch and watched as the heating coil glowed bright orange.  I held it until it got no brighter, about 20 seconds or so, and then released it and hit the start switch.  The generator fired right up and purred like a kitten.

I went topsides to check for water flow to make sure it was pumping OK.  Man, I guess so.  What a mess on the dock.  Good thing no one was there.

I switched ship's power from shore power to the generator and turned on a few appliances to put a load on it.  Everything was working perfectly.   I went down to the engine room to shut the generator down and walked into a steam room.

Uh oh.  I held my breath and reached in and shut down the generator and then flipped on the engine room fan, and then ran out and shut the door.  After waiting about a half an hour, I went back to the engine room.   The air was clear and the engine was cool enough to check things.  Maybe when I checked the coolant level I didn't get the radiator cap on tightly?  It looked OK.  I started up the generator again and watched.   After some time, I saw a few wisps of steam coming from the radiator cap.

I can handle this.  Just take it one step at a time, from the easiest fix to the more difficult.  It might be a bad radiator cap.

I took both generator caps and a Ford Lehman cap to Autozone, where the lady there was totally useless.  She asked what kind of car I had (while munching on a sub sandwich).  When I told her it was a boat, she looked at me with an exasperated look and waved her hand at a wall of radiator caps.  She handed me one.  It was the wrong size (you measure a cap by the full exterior width, the width of the fill, the height, and the pressure release.  All were wrong.  I took my caps and went back to the boat.

I later went to a local auto part store, and the fella there was really helpful.  Withiin five minutes I had all the correct caps.   Back at the boat, I replaced all the caps and fired up the 7 1/2 KW generator.  It still overheated.

Next step, the thermostat.   The problem here was finding it.  According to Onan, it is in one of three places.  Why three places?  Because marine manufacturers like to mess with people's minds.

I decided to go for the easy one, which would be to remove the expansion tank.   I squirted the bolts with PB Blaster.

PB Blaster is a great penetrating oil, so add this to your list of must-haves, along with ratcheting crimpers.  It saves a whole lot of cuss words.

I waited a minute or so for the oil to penetrate, and then popped the bolts right out.  I pried up the tank, and sure enough, there was the thermostat.

See that little green hole under the tank?  That's where the thermostat was.  

I took the thermostat up to the galley, got the nastiest pot we own, dropped it in the water, and turned the burner to its highest setting.

Within a few minutes, the water was steaming and the thermostat opened.  It functions properly.

The next step is to flush out the cooling system.  I believe the raw water side is fine because it pumps water like crazy.  It must be a blockage in the fresh water side.  Now to figure out how to flush it.  Luckily, I have an Onan Master Service Manual.  It must be in there somewhere.

Since I already had the pot out, I used it to heat up chicken noodle soup for lunch.

Maybe I'll flush the cooling system today.  Maybe not.  It's going to be another beautiful Golden Isles day.


  1. Dave: I would look into the heat exchanger next, including the plumbing from the FW pump to exchanger. Look for little pieces of impeller.

    1. I think you're right, John. Read tomorrow's blog.