'94 Camry V-6. Open highway mileage is always easy to peg, and my machine (with 120k miles) is on the high end. On an annual trek of 640 miles. I get around 32mpg, and have gotten as high as 33.6. With air conditioning off and holding the speed to 65mph ±.

City mileage has always varied a lot. Usually around 17. Well, last week I had the oil changed and switched from 10-40 to 5-30. Overnight I noticed a bump in MPG of about 5-8 MPG. Am I dreaming?

 

that's weird!I haven't seen anything like that before.

 

Isn't one of the two reasons for using Synthetic Oil over Petroleum that fact that for any given viscosity, there is a mileage increase. The Synthetic is more "slippery". Thus, less drag from the moving engine parts.

The other reason is that Synthetic doesn't break down under high temps.

 

yep, would be my thought. 37-40 mpg on your special trip?
If it's confirmed let us know the details...

wouldn't get too excited over one data point, I try to wait for at least 4.
best data consistency I've found is by filling up the same time each fill-up.
I do fill-ups now in mornings, < 8AM, when it's cooler, btw.

 

The long trips were repeated several years in a row. Twice annually. That was with the heavier oil. On about 5 or 6 journeys I got around 32 mpg, and on one trip, 33.6.

Short drives in traffic here in Santa Monica vary a bit, but usually the result is 16-17mpg. The increase following a change to 5-30 is on the short drives with stop and go driving. I won't have to fill up for another 10-15 days, and then I'll have an exact number.

But, I'm estimating based on the fact that the needle is at the half tank point, and the odometer is clocking about 40 elapsed miles more than usual. And the driving pattern isn't different. I'll give an update when I fill up and then again when that tank is empty and refilled.

 

Disappointed. Refilled tank after 220 miles of city driving. The average was on the low side of 15mpg.

One recent evening, I crawled for 90 minutes through 4 miles of creeping traffic. I think that ended the good-luck run I was temporarily having.

 

appreciate your following through and (unfortunately) closing out the topic; not all do that.