Fuel Economy drop at 3500miles after oil change?

[NZ-FE Vios]

As the topic states. Has anyone else noticed a drop in fuel economy after 3000-3500. My calculations put me at 3-5mpg less city. I run the car regularly and under same conditions and always calculate at fill up. I usually end up putting 9-10 gallons worth at the same station.

Thinkin about doing mine at 3500max.

Edit: I always have the dealership change it using their syn-blend and oem filters.

[Happy Little Pony]

It's highly unlikely that your oil has anything to do with your drop in gas mileage. That's really not very many miles.

This might seem a little crazy, but they had a similar question on the "Car Talk" radio show recently. A woman claimed she could tell her car was due for an oil change because her MPG dropped. They came up with the conclusion that what was really happening was that when she went to her dealer to get the oil change, the shop also aired up her tires. The correctly inflated tires gave her an immediate improvement in MPG's. This improvement slowly deteriorated over the months as the tires lost air. The fact that the car was also due for an oil change was coincidental.

[NZ-FE Vios]

I keep my tires at 42psi. I check them at least once a week. I should do a few highway tests on my theory. That way its much easier to make sure conditions are much more similar.