Synthetic Oil Decreased MPG??
 

I went in to the dealer last weekend for my 2nd oil change and this time I got Mobil 1 Synthetic Oil instead of the standard oil that they offer (not sure what it is). After getting the oil changed I've noticed that I haven't been getting nearly as good of a MPG average.

I do 75%+ of my driving on the interstate so I used to get 24-25 mpg averaged across a whole tank of gas. However, when I filled up last night the reading said 22 mpg for the tank that I had filled up right before going to the dealer for the oil change. I'm only like 50 miles into my 2nd tank but it's at 21 mpg right now. I'll be doing 80-100 interstate miles tonight so I'll see how that affects my average.

The only other thing I can think of that is different now than before is my use of the A/C. I have been putting the A/C on Auto lately instead of putting it on a low setting. This may make a slight difference but I wouldn't think this would affect my mpg by such a large amount.

I'm 400 miles into the first synthetic oil used in the car so maybe I just need to wait a little longer.

Anyone experienced something similar whether it's changing the type of oil or increase A/C usage?

Other factors are at work here, not the oil. And as far as the A/C goes, it is either on or off, meaning that no matter the setting, the compressor is going to be either on or off. When on, it engages and disengages at relatively the same rate no matter the temp or fan speed setting. And yes, using the A/C will slightly decrease mileage because of the extra load on the engine. My best guess is it has more to do with the increasing summer temps outside.

.... all I can say...:bowrofl:

X2....:tup:

op - you are aware our cars use 5w30...(?) if you put thicker oil i suppose it could loose mpg...(?):icon14: