FLUCTUATIONS IN OIL TEMPERATURE IS VERY NORMAL
Both when starting up and during operation it is quite normal for the oil temperature to exceed the set temperature. It happens for a variety of reasons. After-warmth in the heating elements is one of the reasons. When the temperature sensor detects the correct temperature, the heating elements turn off. However, there will always be some after-warmth which causes the oil to rise slightly above the desired temperature. It is normal and does not harm either machine or oil.
The fluctuations in temperature are also due to the amount of oil in the vat. The less oil in the tub, the less oil is there to absorb the heat and a small amount of oil will also have a larger drop in temperature when food is put down in the hot oil.
The type of food you fry also affects the temperature of the oil, and thus the fluctuations. If you deep fry large portions of fish fillets it affects the temperature more than if you put a small portion of French fries into the oil.
Therefore, it is quite normal that you experience fluctuations in temperature. The graph shows how the oil temperature fluctuates during operation.