I got my first oil change (5000mi) at the Stevens Creek Toyota in California because they gave it to me for free (the dealer I bought the car from was a bit sketchy and I complained when they called me to ask how the service was). Just last week, I changed my oil myself (10000mi) to Mobil 1 (full synthetic). In the last week, I've noticed a consistently higher mpg of my car. Before it was consistently getting around 45mpg, but it's been slowly climbing up to ~48 (still increasing). Do you think it's possible that they didn't change my oil? I know that synthetic should help a little, but I didn't expect it to help this much, that's why I suspect some foul play. When I removed the filter, there was a lot black pieces that overfilled from the top, is this normal? Is there any way to check whether or not they actually changed my oil?
If you saved some of the oil you drained, you could submit it for used oil analysis. Otherwise, no there is no way to determine if the dealer really changed the oil. I know of some OCD folks who will put a piece of tape on the hood, and on the filter, to determine if the car really had an oil change. If you have to worry about it that much, just do it yourself I do my own oil changes as I can use a far superior oil, and have the assurance the service was performed correctly
I think you are just seeing the increase in MPG from completing the break-in period combined with warmer weather. There is no way to determine if the dealer changed the oil at 5K since you have already changed to Mobil1 at 10k. Don't worry about it, just enjoy the increased MPG.
But I hit 10000 miles before I did the oil change. At it was an instant change... Oh well, I guess I just won't go back. I hate that dealer anyways. I guess driving 5k miles w/o the first oil change won't hurt my car too much.
Ghatid If you get used oil analysis at your next oil change, the results will tell you if anything got scratched etc. in there. I am always recommending this because for $20 to 30 you get a real good look inside the engine.