Went on a 1200 mile road trip with a friend of mine, rented a Le Sebring Convertible. When my buddy filled up for the first time I noticed that he filled the tank with premium. I told him he was crazy to use premium in a rental car. His response was: better gas better milage, so saving money on the long run.

He drives some high end cars, so I can understand he uses premium for his own cars, but for a rental.

Is he right, or just a good consumer...

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

There are more than a few threads in the technical forums discussing grades of gasoline and octane readings. Better MPG? It depends on too many variable to just say that premium unleaded is better than regular unleaded.

The key element is the octane rating, which is currently an averaged number, representing the fuels resistance to detonation. The higher the rating, the more resistant the fuel is to premature combustion. Higher compression ratio engines do require higher octane fuels to avoid predetonation, or ping. Race fuel is in the triple digits. Modern cars have knock sensors (seismic devices) that can adjust the timing to eliminate or reduce predetonation, but do so with a loss in available HP. So in a modern car, using the proper octane for the car should get you better MPG, but putting premium in a car that doesn't need it would be a waste.

That's my conclusion, in a nutshell. The 190e got mid or premium; the Mustang does not. The VW bus gets it as it pre-detonates easily on warm days. The Jetta gets neither.

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1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

How about using premium to improve the smog numbers? Mine's coming up. Or even octane boost?

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5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)

jim
just make sure to get her good and hot before you get to the shop.

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'O=00=O'
bmw 2002.
long live the legend

Yep, good and hot is the way to go. You can loosen up the valves a little too. That seemed to help my old Isuzu trooper.

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-livin' in the terminally flippant zone

I noticed that the fuel requirements for a 2000 Saab 9-5 Turbo V6 were only 89 Octane which is mid grade are around Milwaukee but it was run on regular to mid grade for 70k miles with no problems. Does anyone else have their turbo Saab run on regular or mid grade fuel?

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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power!
1977 6.9 3(A) - 84k