Re: Onan 6500 genset can't put out rated power, output fluctuates

Bill Kinney


If the engine speed is changing, I would guess that the likely problem IS with the engine side. The engine speed is mechanically governed, and shouldn’t vary more than a few percent under any load.  As the engine speed varies, the frequency of the power will change as well. This can put some of the plugged in equipment at risk of damage.

I think it is unlikely that the engine power output could be half normal without other problems. But DO check fuel availability.  A weak primary fuel pump, or clogged fuel filter could be the issue by choking the engine when it demands more fuel to maintain speed under higher load. If there is sufficient fuel, then the governor and/or injection pump are the next candidates.

It is also possible that there is something wrong with the electrical control of the generator that is overloading the engine, but I can’t think what that might be, assuming that the voltage stays in specification before the engine starts to struggle.

Bill Kinney
SM160, Harmonie
Fort Lauderdale, FL

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