Back around the beginning of March, 2004 I switched from Pennzoil 5W-30 to Redline 10W-30 and immediately noticed a 7.1% MPG increase. The car also seemed peppier. I kept wondering if the increase was because of the oil or because the refineries switched to a more summer blend gasoline. I queried Mobil and here is what they sent me:
"There are actually a number of volatility changes that occur over the course of the year in most parts of the country. For Chicago, they are listed by RVP but note that other volatility characteristics associated with the RVP change, as well.
Month RVP
Jan, Feb, Mar 15
Apr 13.5
May 9
Jun - Sept 15 7.2
Sept 16 - 30 11.5
Oct 13.5
Nov, Dec 15
Except for the large step change that generally occurs in mid to late May, in time for the June 1 deadline, most of these transitions take place as new gasoline replaces the old inventory at the service station.
As a general rule, fuel economy is better when the volatility of the gasoline is low. But it is hard to measure the difference because of many other things that change from fill up to fill up. Engine tune, tire pressures, city vs. Highway driving are just some of the factors that have at least as big an effect on fuel economy as does the switch from winter to summer grades."
This is very interesting info. It also indicates that the increased mileage was due to the oil. (The gas I was using the entire time was Mobil regular, and all the driving was similiar city driving.)
"There are actually a number of volatility changes that occur over the course of the year in most parts of the country. For Chicago, they are listed by RVP but note that other volatility characteristics associated with the RVP change, as well.
Month RVP
Jan, Feb, Mar 15
Apr 13.5
May 9
Jun - Sept 15 7.2
Sept 16 - 30 11.5
Oct 13.5
Nov, Dec 15
Except for the large step change that generally occurs in mid to late May, in time for the June 1 deadline, most of these transitions take place as new gasoline replaces the old inventory at the service station.
As a general rule, fuel economy is better when the volatility of the gasoline is low. But it is hard to measure the difference because of many other things that change from fill up to fill up. Engine tune, tire pressures, city vs. Highway driving are just some of the factors that have at least as big an effect on fuel economy as does the switch from winter to summer grades."
This is very interesting info. It also indicates that the increased mileage was due to the oil. (The gas I was using the entire time was Mobil regular, and all the driving was similiar city driving.)
