No for Gas. My Mileage dropped off right after my oil change in the early fall. When I dropped it off was getting 8.2L. After the oil change and there f- up of the front camera when installing the block heater and scratching my right front fender / bumper. The mileage dropped to 10L. I staring to think he put the wrong weight oil in.Does Canada switch to a different gas formulation during the winter like many states down here do? I know our winter gas is oxygenated and the ethanol content varies which can drop your gas mileage.
I had an oil change in another make of car and they mistakenly put 0W/20 in instead of the recommended 5W/30. There was a significant increase in efficiency. I had them drain it and put the correct oil in after about 1,000 miles. Even though the car used less gas, it was not the recommended viscosity. With the correct viscosity it was back to my normal MPG.You have a good point with the oil weight. We run 0W/20 and if they used say 5W/30 that would increase engine drag and lower the mpg.