CinciPrius said:
Also be sure to check your oil level - it should be below the full mark - if it's at or above the full mark, that will also hurt your gas mileage.
Lots of folks have reported mileage increases at 5k. The reason has less to do with oil level and more to do with the natural break in of the vehicle. Now, Toyota products are very well engineered and the tolerances of manufacturer are very tight, so break-in isn't so much a special period of use where you have to treat the car differently, however it is more or less the period of time where the moving parts of the vehicle set in to a natural orientation, alignment, placement or however you want to describe it.
Now, most of us have experienced a couple different stages of "break-in". I know I noticed the car becoming more efficient before my first oil change, around 3k. And as I approach 10k I notice greater efficiency just about every time I fill up, although it is starting to plateau. I keep my tires at 40 front and 38 rear and usually check them about every 2 weeks and adjust as necessary.
But here is the real kicker with regard to my experience. My oil has always been "overfilled". What is overfill? Well, some define it by the marks on the dipstick. I find that entirely questionable because a dipstick is not a precision instrument. It includes no specific graduations indicating oil height in pan or indicating specific volume in milliliters. It is just 2 dots embossed on a metal rod which is supposed to give us a general idea of how full the sump is.
If the dipstick were a precision instrument I would take it very seriously, however it is there to give us a general idea of the safe level of oil in the sump, not to give us a specific measurement of oil in the sump.
Oil overfill would have a negative effect on FE if the sump was so overfilled that even when the oil system was pressurized there was oil in the sump that was being struck by the crank as it spun. That would put resistance on the crank, along with creating a situation of oil foaming because the crank would be hitting the oil in 4 places very quickly and thus agitating the oil as if it were in a blender or food processor. In fact, if oil overfill was such that this condition was occurring, it would be a short time until the possibility of engine damage occurred. FE would be the least important problem that an engine overfilled to this level would be suffering.
So, the book volume of oil in the sump is 3.9 quarts; which is 3.690 L. 4 quarts is 3.785 L. That is a difference of .095 L and .10 qt. That isn't enough liquid to appreciably change the oil level in the sump so that crank strike happens, let alone an oil foaming issue or even a loss of FE.
