[Amel Yacht Owners] Onan Generator Troubles

Stephen MORRISON <steve_morrison@...>

Duane. I had these very same codes and my generator often shut down within the first two minutes of running. I had Cummings come out and look it over and it turned out to be the exhaust sensor. A little fumbling with the wires and it has run smooth ever since. I did order a spare sensor to have on hand but the Cummings service guy said I could also just connect the wires directly and bypass the sensor as a fix if needed as in his opinion, so long as water was running through, which has its own sensor, the exhaust cannot get hot enough to be a problem.

All the best,
Steve Morrison

On Apr 23, 2017, at 11:01 AM, sailor63109@... [amelyachtowners] <amelyachtowners@...> wrote:


The generator has my attention...again.

This morning it shut down with a "3" fault code, which the manual said requires service by trained personell.  I then read there is a second level code accessed by pressing the STOP once.  I got the "58" fault code, "High Exhaust Temperature".

I checked:
-Impeller: it's all there, no apparent damage.  Although strangely one of the vanes was bent the wrong way at the "pump side".
-Coolant or raw water leaks: none apparent.
-Coolant level: unchanged in the surge tank.
-Temperature of the water in the muffler: it was surprisingly at room temperature???
-Seachest for blockage: it was clear.
-Exhaust elbow: not particularly hot (water didn't sizzle).

I tried to let it cool down and restart it so that I could get a temperature on the exhaust elbow.  It would start, but would not run for more than a few seconds, and then flashed the same fault code.

About eight months ago I had a "High Engine Temperature" and found that the exhaust elbow waterjacket had a hole in it, and the heat exchanger would not hold pressure.  I replaced them both and haven't had a problem with high temp's again until now.

I did check that water was being ejected in the exhaust immediately after starting and it was normal.  I'm perplexed, what could be the problem?

Could this be a result of the freshwater leak into the generator from the watermaker flush valve?

Wanderer, SM#477

Duane Siegfri

Wow!  Steve!  You were exactly right.  One of the wires on the temperature sensor was disconnected...the screw had fallen out.  I'm amazed I didn't notice that when I was looking at the exhaust elbow and trying to determine whether it was hot.

As I write this the genny is humming along, happy as a clam, pouring amps into the batteries and making water.

Are you going to be in Brunswick this summer?  We're headed there in early July for hurricane season.  Be nice to meet and buy you a beer or two!

Thank you for the help!
Outside No Name Harbor, Key Biscayne

Bill & Judy Rouse <yahoogroups@...>


Use your ohm meter to check for continuity between the terminals on the temperature sensor on the exhaust elbow. That temp/sensor/switch is normally CLOSED. As the exhaust elbow temperature rises above the switch tolerance, the switch OPENS. 

Remember there are a number of sensors in the shutdown system, and these switches will fail. I replaced the exhaust manifold temperature switch and the waterflow switch because of failures. I also had one situation with a loose connection on a switch.

Did you use your laser temperature gun to measure temperature? The normal temperature of the exhaust elbow is about 50C and the normal temperature of the coolant is about 80C. Were these in range? How many hours since the last impeller change?

The impeller blades can look OK, but the impeller be defective:
  1. I have experienced the rubber part of the impeller becoming unattached to the metal hub, resulting in the rubber impeller slipping on the hub, but only after the generator reached operating temperature...this was a Globe brand "Run Dry" impeller...DON'T EVER BUY THOSE
  2. I have experienced the tiny key on the impeller shaft wearing and causing the metal hub of the impeller to spin on the shaft.
  3. I have experienced the blades on an impeller wearing in such a way that they become shorter and cannot push as much water. This usually happens to boaters who only replace impellers when they lose blades, rather than at hour limit. My experience in worn length of impeller blades was also with a Globe brand "Run Dry" impeller...DON'T EVER BUY THOSE. I believe the Onan impeller should be an OEM impeller and changed every 300 hours or 12 months, whichever comes first.
I would bet big odds that you have an impeller problem because one blade was in the opposite direction...I believe that with a good impeller and pump, this should never happen. I believe that you may have one of the above situations going on with the impeller and you should not only replace the impeller, but also, with a high degree of certainty, eliminate the potential problems that I listed above.

HINT: It is always easier to remove the Onan saltwater pump (two bolts) to replace the impeller. Have your wet-vac available and a large shop towel to eliminate any possibility of saltwater getting on anything.

Good luck, and I hope this helps.


CW Bill Rouse
Admiral, Texas Navy
Commander Emeritus
Amel School 
720 Winnie St
Galveston Island, TX 77550
+1(832) 380-4970