My High mileage (277k miles) 2012 Honda told me i needed an oil change. Went 1000 miles over due to being busy. Due to being busy still I let Walmart do the oil change. Guy asked if i wanted the kind on the oil cap, i said sure but that it needed full synthetic High milage. He said they all get the same miles between changes. Had a quick red flag back and forth where i try to explain that im not asking for more miles between changes, that it needed oil designed for higher mileage vehicles. He never understood so I just told him to put regular in there.
Anyway ever since then it’s been dropping my mpg every day. Used to get 39to 40ish but now it has gotten as low as 34. Not sure what they could have done to cause that but any advice would be appreciated. I drive around 450 miles a week so this is starting to hit my wallet.
I would guess a few things. Could be wrong viscosity oil, could be something left disconnected in the induction system while checking the air filter, though this would set a code and CEL. They may have set your tire pressures too low as well.
In the future if the person doesn’t understand something as basic as high mileage oil, take your car somewhere else. They don’t have the knowledge to be qualified to be dealing with cars if they don’t know what high mileage oil is.