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Re: [Amel Yacht Owners] Onan Generator Troubles

Bill & Judy Rouse <yahoogroups@...>
 

Duane,

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.

Best,

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