One of the tests would be viscosity. He got the gel point, checked his viscosity and found that there were significant differences, even though it was within specs. The head had caused the oil to break the molecules down. There's always energy and a measure of random energy is temperature. Temperature is a basic measurement in degrees - Fahrenheit or Celsius.
Temperature is measured with a thermometer.
There's always time rate of change involved in the transfer of heat energy which is temperature. We measure temperature from that time rate of change of the energy going into the thermometer. When we have temperature, we say the molecules are wild and they're going in all directions. These molecules are moving in all kinds of directions with temperature. We have a long, snaky looking molecule.