Got stuck in a bad spot this weekend and decided to get gas at the local SAMs Club. Filled up with their 91 grade.

I was on fumes and was really pressed for time and my normal Shell station was 10 miles and 30 minutes out of my way.

Now, 1 day later, and my car won't get off the line at all. Hit the gas while cruising to pass a slower car and there is a major delay and the motor just falls on its face.

Now I have 7/8 of a tank to muddle through.

 

You might consider picking up a bottle of octane boost at a local auto parts dealer. All that preignition can't be good for the engine.

 

10XF, the gas that you got varies from station to station, and possibly even at the same station depending on how long the gas has sat. In this case, because a lot of stations are shifting from the winter blends to summer blends right now, the gas in the tank may have been manufactured back in say September and has sat all winter long.

Like was mentioned, you can try a bottle of octane booster or you can try a little bit more driving (getting the car down to say 5/8th of a tank and then refilling at your normal station to help minimize the amount of bad gas that the car is seeing at any one time.

 

Don't waste your money on bottled octane boosters. Most don't do anything at all , the others that do work 'raise' the octane by 1/10th of a point per bottle.

If you're convinced that you got a bad load of gas, go back to the retailer and complain. There might be others that have done the same.

 

I think you just got a bad batch of gas, possibly from the bottom of the tank mixed with water, or who-knows-what. While I wish we would have higher than 91 octane fuel available here in CA, the quality should be decent and you should not feel any performance difference from brand to brand or station to station. Nearly all gasoline is manufactured at the very same refineries before they are being shipped out to brand or discount stations.

 

+1

 

You'd gain nothing even if octane levels higher than 91 were available. The number has nothing to do with quality in any way, just a reference number for resistance to detonation. 91 octane is all that's required to achieve detonation-free operation and full performance from your engine. Anything higher is wasted money.

 

As more and more gas stations shift to 10% ethanol 90% gasoline blends, performance will get worse. Since ethanol has less a less BPU, it is going to give a worse gas milage, and more importantly, significantly worsen performance. The gas station closets to me uses this 10% to 90% blend even in the 93 (its a BP). The other BP I fill up at has 92 but it has no ethanol and there is a significant difference! Since our cars are "performance" cars, we need to use 100% gasoline to get optimal performance from the gasoline. Sam's club, Costco, QT, they all have the ethanol mixed gasoline. Go to any shell or BP and ask them if they mix, if not, then use that because trust me, your car will love it and you will too!

 

E10 gas might be new in some areas of the country but much of North America has been routinely using it for 20-30 years.

There is a small mileage penalty (around 3%) but otherwise no difference in performance. Some people who insist upon using pure gas, if they can find it in the correct octane range, are also finding that it carries a 7-10% price penalty.

 

Must be a special kind of arithmetic you're using.


Grade for grade, market for market a 7-10 percent price penalty would not exist.

That is, the pricing between different brands of 91 octane is going to be almost identical in any given neighbourhood in North America.

To get a 7-10 percent difference, one would have to be comparing between grades.

For example 87 octane versus 91 octane.

Then, and only then will there be a cost differential.

But, in that situation volume consumed per mile with the higher octane is less than that with the lower octane due to the ecu being able to adjust ignition timing upwards. Volume consumed per mile within an octane grade is also less for ethanol free gasoline as opposed to ethanol blended fuel due to the reduced energy of the ethanol.

The above is the expected and known behaviour of gasoline. It is also observable using obd-ii logging.

There are also sites which track the price gaming of gasoline retailers. Their prime output is MP$. Miles per dollar. That's the number that matters when peering into the wallet.

The long term result is that on a MP$ basis, it is often a wash. Pay less per gallon and use more gallons or pay more per gallon and use less gallons.

For new members to JF, the above is essentially what I have posted multiple times.

 

plums-

You really need to get that chip off your shoulder.

Case in point:

An acquaintance in the US sent me a picture taken at a local gas station asking for advice. He's not mechanically inclined in any way but wants 'the best' for his car. He's heard all the sky is falling horror stories about E10 and just wanted the truth. The station now offers E10 in three different octane level and one octane level of fuel that's 'pure gas'.

The pure gas is 89 octane. The price difference between the pure gas and E10 of the same octane level was $0.33 which made it 8% more expensive and in fact more expensive than the 92 octane E10 available at the same pump.

 

I think what he means is that the E10 will net you less mpg but it costs less. The pure gasoline will net you more mpg but costs more. So it's a wash only if the mpg hit comes out to be the price difference.

 

Exactly, putting aside the fact that the car in question requires at least 91 octane, the pure gas was 8% more in cost to avoid a 3% decrease in mileage. Bad economics.

Comparable to the E85 debacle where the fuel is frequently not priced low enough to offset the dramatically increased consumption.

 

I would never run less than 93 octane unless I had no choice in a high horsepower boosted engine. An engine can be designed to run on lower octane fuel because it is not available in all areas but that doesn't mean that it is going to run at its full potential or it won't seriously pull timing if the octane is too low and it is really hot out. It's been documented all over the place that many boosted (and some non-boosted) engines that technically can run mid-regular grade gas perform significantly worse when not fed premium.

Here is a note from a GM engineer from our college's car club forum to a guy with the 2.0T ATS. This was specifically around some of the boosted ECOTEC motors (which are also technically designed to run on "regular" fuel):

 

Here's what Jag says in the owner's manual:

FUEL SPECIFICATION

Gasoline
Unleaded 91 Octane


This is from the US edition, so we can presume that this is AKI and not RON. Why would an OEM design a car that required a fuel of an octane level (93) not available on most of the continent?

If it's being inferred that more power provided by more ignition advance can be 'unlocked' by using 93 AKI, this would mean that the engine is experiencing detonation while using the recommended 91 octane.

 

There are plenty of car makers that require premium fuel (93+) in their vehicles. It is usually in boosted / high performance / strung out engines. Their cars will run on 91 but it is not recommended. Most modern OEM ECUs are adaptive and will adjust fuel trims / timing based on atmospheric conditions and the quality of the fuel you are feeding it even if they are designed to run fine on 91 or worse. Per the original poster's point, the quality of gas in America overall is pretty poor. You really notice the difference in a high performance engine when running lower octane fuel. I noticed a difference even in my old CTS with a 3.6DI engine.
Both of my old Subarus had separately tuned maps for 91 octane (in case I was in an area without 93), 93 octane and 110 leaded. All three made significantly different power levels and had a noticeable difference in driveability.

 

Most stations by me don't even carry 91. It's 87, 89, or 93. I always fill up with 93 Shell or Mobil.

 

Which is why Jag states minimum 91 octane in some literature. It does not infer that performance or mileage will improve, but simply which way to go if 91 is not offered.

 

BTW, 91 was just an example because it was the wee hours of the morning when written.

I normally pull into SHELL stations and select the premium V-POWER on the far right button.

That would be ethanol free premium then. 91 or 93? I forget.

On obd-ii, this practice nets a change from LTFT=+10 on 87 octane with ethanol to LTFT=+2 on the ethanol free SHELL V-POWER premium. And the effect is repeatable. LTFT directly correlates to the amount of fuel consumed and the fuel consumption computer agrees. There is a commensurate increase in MPG.

Locally, there is no cost differential between the SHELL V-POWER ethanol free and other brands of ethanol blended premium.

By filling a 1/4 tank or more, it is always possible to stick with the preferred gasoline. On trips, the range is great enough to be able stay with SHELL V-POWER so far. The other reason for staying above 1/4 tank is to ensure enough gasoline remains to cool the fuel pumps.

Previously, I followed the practice of a senior chemist at one of the big refiners and tried switching between brands every six months. His rationale for this practice was that each of the refiners uses different add packs and one cleans the effects of the others. This was published in relation to his Corvette. Don't forget, as a senior chemist this practice cost him money. Gas of his own brand is on the company credit card while other brands come out of his pocket.

When it was SHELL's turn in the tank, the differences above were noted and I dropped the practice.

In summary ...

Regular ethanol blended gas gave the least MPG. Premium ethanol blended gas gave better MPG due to increased timing and SHELL V-POWER ethanol free gave the best MPG due to increased energy content.


There you go ... theory blended with real world results.

And since this is a gas thread ... YMMV.

++

 

In most markets, gasoline within a grade whether ethanol free or not will be the same price. The ethanol free will yield better MPG.