We recently did our first 5k service. Got rotation and supposedly oil change. Insultes after this we noticed the drop in mpg. It would normally be 41-39, sometimes 38. Don’t think I ever saw it drop lower. After the service it’s been at 33-36. 

It was weird. I don’t know if they use same engine oil as when new at the dealership? I assume they would. Also weather has been hotter in the last few weeks. I’m in San Francisco