Imperial deep fryer IFS40 pilot lights, turn on gas valve main burners come on run for awhile then everything shuts down main and pilot. You can disconnect the thermostat and the same thing happens, main burner lights for awhile then both the pilot and main go out.

Hi there, it sounds like your thermopile, for the pilot, is failing during use, when this happens, the small DC voltage it generates is less than the gas valve requires to stay open, and shuts off the pilot, which shuts off the main burners. Another thing that could be happening, is the hi limit is opening prematurely, instead of shutting of the pilot at 450 deg. it now is opening at 325, or 225 or 250. Sometimes the sensing bulb gets broken where it pass's through the oil tank causing this symptom. If you temporarily bypassed the hi limit to test this also, and it still goes off, you need a thermopile. If it stays on, check your temp with a reliable thermometer, and see if it reads fairly close to your setting, if so, then you need a hi limit.
Hope that helps, and thank you.