MPG increase after first oil change?

[yardman 49]

Hello all:

I had an interesting experience recently.

A few days ago, I took my 2009 in for its first oil change at the purchasing dealer's shop. I asked what they used, and they said "Valvoline 5w-30". I told them that I didn't want it overfilled, but they replied that they had to put in the "amount that Toyota specifies", and gave me a printout that showed the required 3.9 quarts when changing the filter. Anyway, when I got the car home I checked and sure enough, the oil was about 1/4 to 3/8" over the full mark (this part I posted in another thread, and I've since removed the excess oil based on the advice given there).

Anyway, when driving the car home from the dealer, I noticed that the "instantaneous" MPG when the car was not under load seemed to be higher than I remembered previously. And this even though it was overfilled.

I haven't driven the Prius enough since then to see if my average MPG increases. But I'll be doing a lot of driving the next few days, so I should be able to tell then. Also, as previously mentioned, I've since removed the excess oil. (FYI: prior to the oil change, the oil level from the factory was dead on the full mark.)

So I started thinking about this. Is it possible that the oil that comes in the car from the factory is really a heavier weight oil, or possibly has some other additives that help the break in process? I've seen others write that at about 5000 miles the MPGs will go up as the car becomes broken in. But maybe the real correlation is that the original factory oil has been changed?

Just pure speculation on my part.

[dogfriend]

My speculation is no, the oil isn't a different viscosity. Too many variables (temp, road surface, wind direction) to make a conclusion based upon a single drive home.

[2009Prius]

My factory oil measured viscosity of 20 at 100C at about 2800 miles. The Shell Full Synthetic 5W30 measured viscosity of about 10. So there may be a difference.

[Frayadjacent]

Yeah, one trip of perceived or actual, could be a fluke.

HOWEVER, fresh oil can decrease friction. Keep track of your mileage and fuel consumption, and you'll be able to see an increase over time.

One of my previous cars was averaging about 21mpg. When I changed the oil with Amsoil (after the engine was well broken-in), the average for the first tank was 26mpg. The next was 24, then it leveled out to the previous average.

Also consider that your engine is either broken in or is almost there. It's been noticed that after break in, you may get better economy.

Keep track of your usage and you'll be able to see trends more easily. I use mymilemarker.com. It has an easy to use mobile page that works well on my iPhone. There are some apps, but I like mymilemarker.com since I can easily access it from any computer, and it displays some simple graphs.