Winter/Summer grade fuel mileage difference

[Firebirdjones]

Here is an interesting difference I have found since we have now switched to summer grade fuel about 3 weeks ago.

My wifes Z28 consistently gets 20 mpg around town on a regular basis, all winter long (when roads are clear ) with a log that fluctuates from a low of 20.4 and a high of 21.0. It has had summer grade fuel for the last 3 weeks with a fill up once a week and logging the mileage now shows something interesting. It's lowest reading was 21.6 and the best was the last fillup yesterday at 22.5!!!!

My 02 SS was getting about 19 mpg,,,with logs that fluctuated from a low of 19.1 and had a best of 19.7. Again the last 3 weeks have been summer grade fuel and this car showed the most improvement. With a low of 21.2 and the best was the last fillup yesterday at 22.1.

Both cars drive the same routes, mostly back roads with alot of stop and go, and both cars get filled up at the same station, with Sunoco 94 octane.

Interesting how both cars have picked up slightly in mileage with summer grade fuel.

[Spikito]

Ive never seen summer or winter grade gas, just the three octane ratings, regular 87 super 89 premium 92....i think thats what they are

[Firebirdjones]

Ive never seen summer or winter grade gas, just the three octane ratings, regular 87 super 89 premium 92....i think thats what they are

You wouldn't see it anyway,,,you live in Texas

It's common among the Eastern states, although it's never advertised at the pumps.

[ghettosled]

i never drive the camaro during winter so i cant speak in terms of that car, but on my DD 1996 camry i4 my fuel economy in the summer is usually 30-32 mpg, but during the winter its about 27-28. throw on my ski rack and snow tires and i run 24-25 mpg.

[kf4knf]

What about the Ethanol content of the gas? Did that change at all?

[Bottesini]

In winter you will also have to colder temps which can have a big impact as well.

[Firebirdjones]

In winter you will also have to colder temps which can have a big impact as well.

It would seem. But we just switched to summer grade fuel a little over 3 weeks ago,,,yet we have had warm temps in the 70's and 80's off and on since the beginning of April. We sometimes have warmer than usual winters as well. Last year it didn't even snow until January and temps were in the 60's in December.

They switch to winter grade around October/November while the temps are still tolerable. So in general there are plenty of weeks where temps are warm while using winter grade fuel, and get a fair comparison with summer grade fuel mileage.

As a matter of fact,,,that winter grade stuff is what I complain about in the carburated cars when the weather is warm,,,,,it causes major vapor lock problems and is a royal pain in the rear until the switch to summer grade is made.

[Firebirdjones]

What about the Ethanol content of the gas? Did that change at all?

Good question. Ethanol is not wide spread here in SW Ohio yet. There are plenty of stations that don't use ethanol, sunoco is one of them, which is where I fill up 100% of the time.
But as science will tell you, any ethanol content will lower gas mileage, as to how much would depend on the content.

As far as summer and winter grade fuel differences, I could check with Scott and Gary and get the inside scoop. I do know that winter grade has a lower flash point (as in lower octane so to speak) to make easier cold weather starting and prevent fuel line freeze up. Problem is the lower flash points also make the fuel more susceptable to heat soak and vapor lock, which is where the carburated cars (with lower fuel pressure) start having problems if the outside temps start warming up.

The more octane you throw at it the lesser the problem.