sw686blue

So Costco gas containing up to 10% ethanol is ok for our 997s? I thought it was a no-no and so i was sticking with Shell. I'd much rather fuel up at Costco as they are typically 15-20 cents cheaper per litre.

Fahrer

All of the Shell stations in my area have the same note on their pumps... up to 10% ethanol. These cars are designed to take up to 10% ethanol in gasoline. It should state that in the owner's manual. Newer cars can use up to 15% ethanol.
The ethanol limit has little to do with the engine. The fuel system components ( plastics and rubber used in fuel tanks, fuel lines and seals) that are most affected.

ilovemaui

Costco advertises their gas as “Top Tier” basically meaning it has detergents to clean injectors. I have used it in my cars for years. Not only is it cheaper but you get 4% back if you use a Costco visa. However, like I stated in the opening post I have noticed a drop in gas mileage lately. I’m going to start trying Chevron and Shell to see how they affect my mpg.

Lately I noticed that ARCO has been advertising top tier gas, but I have always shied away from ARCO for my vehicles and won’t start now. Interestingly I filled a five gallon jug for my lawnmower at ARCO about 20 years ago and apparently they did not warn purchasers that they were adding three or four cents to the gallon price if you used a credit card. About two years ago I received a letter in the mail informing me of a class action lawsuit against ARCO and that I was included in the suit because of my one purchase. Several months later I received a check for about $220 for my one purchase. Pretty good return I’d say.

Liste-Renn

It is my understanding that every grade of a gallon of gas has the same energy content (and hence, MPG).

The differences in octane are a function of anti-knock additives. (100 octane gas can be run at much higher compression ratios solely due to additives)

If your engine compensates for lower octane induced detonation, and retards the timing, adjusts the fuel mixture, or lowers turbo boost pressure, etc., etc., then there will likely be a performance degradation. But not likely a decrease in MPG. I would attribute that to environmental factor variations: wind, slope, tire pressures, speed (drag) or even how many times one passes another vehicle with increased throttle.

Ethanol is, as posted above, inconsequential to engine performance at up to 10%- but may negatively impact the service life of rubber/plastic components in the fuel system.

ADias

Same grade pure gas and E10 have the same octane rating. The energy content of E10 is lower.

Fahrer

The differences in octane ratings are a result of different blended components of aliphatic and aromatic distillates as well as ethers and alcohols in the gasoline mixture rather than the use of a chemical additives ( tetraethyl lead was banned many years ago). Aromatics have a higher octane rating as well as alcohols. These latter items contain less energy than the previously mentioned petroleum distillates. One can design and engine to use very high octane but that is not what is normally done for road cars. You car has a certain fixed design and running parameters can be adjusted such as timing, enrichment or boost, if applicable.

The addition of alcohols are part of achieving a certain level of octane rating. It also reduces the amount of energy contained in a gallon of gasoline. Therefore, to achieve a certain amount of power at any given time, an engine would need to inject a bit more fuel if it contains more alcohol than a fuel with no or less alcohol with the same octane rating. So an engine can achieve the same level of power, regardless of alcohol content, but there are consequences regarding fuel consumption.

Nein Elf

In 15 years of making the trip between Seattle and Portland in various vehicles I often see 1 or 2 less MPG on the trip back from Portland, still not sure why though. Almost always fill at Costco. Go figure.

ManoTexas

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