I currently have 55K miles on my automatic 04 TL. I had the oil changed the other day, as well as the air filter. Prior to this I would avg 20-21 mpg with the a/c in city/highway traffic. Now I'm averaging 17-18 mpg. Is this temporary or what?

P.S. I also added Seafoam to my gasoline tank.

 

Probably a temporay decrease as seafoam works the crud loose
Usually 1 can to 1/4 tank of gas os good
1 oz per gallon fuel for regular cleaning
2 oz per gallon of fuel for super duty cleaning

 

Did they use the recommended 5w-20 oil, if they put in something thicker this will robb your gas mileage!

 

The brand of oil and air filter can effect it too, but most likely just a phase
Check your tire pressure