Scotty - My 2014 Chevy Cruze diesel used to get over 50 mpg routinely on the highway, then last November I had the oil/filter changed at a Valvoline shop. I gave them OEM filter to put on and they also put in a new air filter.
Immediately after that oil change, I started noticing my MPG dropped way down, down to about 38-40 mpg on highway trips. About 95 percent of my driving is highway. Suddenly I went from 50-53 mpg average to 38-40 mpg average. The motor runs perfectly though, starts up perfectly, has the same power, etc.... and no check engine lights have ever come on.....I cannot see anything under the hood that isn't connected as well.... so I'm stumped.....
I have had a new fuel filter installed, but it didn't really do much to help, maybe about 2-3 more mpg is all.
Do you have ANY ideas as to what happened? It is very coincidental that the MPG dropped right after that LOF at Valvoline last November. Makes me suspicious they did something (probably by accident) to affect it, but I have no clue what it could be.
I hope you can give some ideas. Thanks in advance.
Mark LaPoint, Virginia, Minnesota