In the week after my car underwent an oil change, the oil temperature indicator displayed higher temperature readings than usual, sometimes above 100 deg C. Why was this so? I did not change my driving style or commuting routine.

First of all, an oil temperature reading above 100 deg C is not abnormal.

In fact, oil temperatures in normal driving should be between 95 and 110 deg C for optimum engine oil performance.

You need to be concerned only if your engine's oil temperature exceeds 125 deg C.

On the other hand, an oil temperature reading of 90 deg C or less when the engine is warm and running is also cause for concern, as this would be below any engine oil's rated operating temperature.

It is also important to ensure that the correct oil has been used in your car's engine, which will make a difference in your oil temperature reading in day-to-day driving.

Always check the owner's manual of your car to make sure that the engine oil is the right grade and has the correct viscosity, as advised by the manual.

Do note that a retrofitted oil temperature sensor may not be accurate or ideally located to measure the engine's oil temperature.

Shreejit Changaroth