Mileage test results

This is in response to these threads:

Do I really need premium gas? (VW Passat car question)
Premium Gas
Gas in Diesel Engines

And Una’s Staff report from 2004, and this Car Talk column from this past spring. I have placed it in this forum per Rico’s suggestion.

In the first thread above, I had mentioned that I would run my tests and gather more data again. In short, I was gathering data on mileage using different grades of gasoline. I waited until summer started and school was out, so my A/C usage and traffic patterns would all be similar. [ 1 ]

Vehicle: 2004 VW Passat. Manual Transmission. 4 cylinder w/ Turbo. VW recommends 91 Octane.
Prep: I waited until summer, so A/C usage and traffic would be consistent.
Conditions: Daily commute. Mostly suburban driving. Very Little Highway. Some start/stop.
Blend: I would fill up after using a quarter tank alternating between 89 and 93 octane averaging about 91 octane.[ 2 ]


Octane	Miles	MPG	Time 	Average	Fuel	Fuel	Price per	Costco/BJ's	Costco/BJ's
Rating	Driven		Driven	Speed	Used	Price[3]500 miles	Price[4]	Price per
											500 Miles
87	521.5	28.6	19.617	27	18.234	$2.822 	49.336		$2.795 		48.864
89	568.1	28.6	19.183	30	19.864	$2.995 	52.360		
93	570.6	29.3	17.55	29	19.474	$3.126 	53.345		$2.859 		48.788
Blend	424.2	30.3	14.6	29	14	$3.061	50.503		

Conclusion: Due to the better mileage with the blend, the cost per distance 87 octane and the blend (91) is negligible. While I could save money using 87 octane, I did experience sluggish acceleration and lessened performance. Personally, I’d rather spend a dollar more every 500 miles and know that my car will take off if necessary.

[ 1 ] We have had a heat wave here for the last week, which may have skewed the 89 Octane results.
[ 2 ] The Blend Data is not as complete, as we were about to take a road trip, and I didn’t want to skew the data with an additional 100 miles of Highway driving.
[ 3 ] Price take from AAA website for the Charlotte, NC region.
[ 4 ] Price recoded from the sign outside BJ’s last night.