Kohler generator overheat issues?

[CurrentObsession]

1999 kohler 7.3e

Overflow bottle on the side goes from empty to full back to empty within minutes of running and shutting down.

Recently installed new impeller and coupling and radiator cap. Removed and confirmed the thermostat opens at 165 degrees and the heat exchanger is flowing well. Replaced antifreeze with new 50/50 premix.

Mechanic I spoke with says there is a pressure relief cap on top of the unit that helps burp the coolant and even showed me one in his shop but my unit does not have anything similar that I can find.

 

[Grub54891]

Well, your cap is pretty rough looking. I’d replace that. All the ones I’ve worked on had a small plug that you had to take out on that raised area to burb any remaining air out of the tank. In my opinion, poor design. If it wasn’t burped the set would shut down.

 

[km1125]

Have you used an IR gun on the motor to see how hot its actually getting before it shuts down? And is it shutting down itself, or is that when you shut it down when you're done using it?