tell me, in the days of microprocessor-controlled engine timing....

you are a car rental company. you rent vehicles that use regular. you rent vehicles that use premium.

how do you fuel your fleet? regular across the board and let the engine control module adjust the timing accordingly. or do you fuel selectively based on the vehicle manufacturers recommendations?

i ask this because hertz rents the majority of its vehicles that are intended for 87 octane, but rents some in its premium collection that are supposed to be fueled with 93 octane. but i have concluded that all are fueled with 87 octane gasoline.

am i right? am i wrong?

The last time I was at a rental car agency I saw two grades being used.

Haasman

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'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)

Thats a good question, and octane was one of the subjects in a new Q/A column in this weeks Wall Street Journal.

Mercedes benz is very specific about how the car should be used on their premium cars if only medium grade gas is present, no more than 2/3 throttle, no full throttle, no more than 3K rpm, refill with premium as soon as possible.

Rental cars get rid of their cars at what fixed mileage? and if any probems were to develop from using the wrong gas the car would probably be long gone from their fleet.

Could the wrong fuel grade cause an issue where potential litigation forces rental fleets to stock two fuel grades?

most manufacturers set their cars up so that if you put the wrong gas in the tank, it doesnt explode, because if it does its a warranty claim.

its either short sighted, or really brave to sell a car in the usa that wont run if you put the wrong fuel into it.

i live in the mazda world, and we miss out on a lot of cool cars because we (the usa) complain too much.

that is exactly right. they have to because they know some people will put 87 octane for cars that specify 91 (on the flip side, there are people that waste money by putting high octane in cars that don't recommend or need it). On older pre-OBDII cars you could get more performance out of car by chipping computer. That was generally doable because chip would set fuel/ignition/timing curves so car would make more power but at the price that if you don't use 91 octane engine may blow because of knocking. If you search you will find info re: how US 300Es have a resistor that retards timing just in case 87 octane is used, whereas the Euro ones instead of a resistor have an adjustable thing that at the regular setting has no retard (more power than with retard) but requires high octane, but it can be adjusted to retard timing if you are somewhere where you can't get high octane.

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2005 Mercedes C230k sport sedan, 6 speed
1987 Porsche 924S - 968-engined track car

Most modern engine control systems have enough timing authority to keep "premium fuel" engines out of detonation if 87 PON fuel is used, and manufacturers are getting away from their dire warnings of "engine damage" if less than the recommended octane is used.

New Corvette owner's manuals say that 91 PON is recommended, but NOT required. This is for the 6.0L 400 HP base engine, which has a CR of 10.9:1.

The new LS7 7.0L 500 HP Z06 engine's CR is 11.0:1, and the same applies.

What you loose is some power, especially at the low end, and fuel economy might be worse, especially in stop and go driving, but probably won't be affected at freeway cruise speed.

Duke