I have a Groen 40 gal propaine tilt skillet. I'm wanting to use it on my food trailer as a deep fryer for festivals. I've only filled it with 9 gallons of oil and I can't get it to heat up above 300*. Has this happened to any of you? I know in places I've worked we've shallow fried in tilt skillets before. I read on some other threads that they can be used for deep frying, so just trying to figure out my issue. The thermostat is turned up to 450 and the flame with shutoff well before the oil gets anywhere near that.