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regular fuel advice

5K views 20 replies 16 participants last post by  Administrator jsvette 
#1 ·
Hello forum, I have a full tank of regular fuel. will i do irreparable harm unless i siphon this out? thank you
 
#3 ·
I think the computer would adjust the engine to keep it from knocking, but you could always add some octane booster.
 
#7 ·
Welcome to our forum tcarnes7! As Glen suggested just drive it until its about half full and top it with 91. The computer will take care of everything else. Enjoy :cool:
 
#11 ·
I believe in Canada the reference octane for premium is 91 nationwide. Petro Canada has a 94 but it's their special blend. 91 in Canada should be fine. 91 in the US is for higher altitudes (or California). Near sea level 93 is considered Premium and is what you should use.
 
#16 ·
Refiners are still blending gasolines as if it was still 1970, with carburetors. Back then, there were no controls on cars to compensate for altitude, and no knock sensors. It was, and still is, common refining practice to blend gasolines intended for distribution in higher altitude areas to a lower octane specification than gasoline intended for distribution at lower altitudes. So it was common in many places to see 85 octane regular, and 90 or 91 octane premium. And it still is. As for California, the strict limits on aromatics make it hard to blend 93 octane fuel at reasonable prices, so fuel sold there is mostly 91.

In fact, long ago, it was common to see 91 octane premium even on the East coast at sea level. But as time marched on, refiners invested in refinery units that allowed them to blend higher octane fuel, so 93 is now typical.

By the way, in the old days, when oil companies advertised their octane ratings, it was the "Research octane" rating, which is typically about 10 points higher than the "motor octane" number. By federal mandate, the number now posted on the pump is the average of the motor and research numbers. So 93 octane today would have been advertised as 98 octane back in the 1960s. The highest research number octane commonly sold on the East Coast back in the 1960s was Sunoco 260, which typically had a research number of 103 to 104. Most premium fuels had research numbers from 99.5 to 101.5. I was a young engineer working for Exxon at that time, and had access to this industry information. Those of us with muscle and high performance cars loved having access to that information. Believe it or not, some of the highest octane fuel back then was sold by the "no name" brands, as they felt they were held to a higher standard by their customers, and did not want their customers leaving them because of complaints that their cars knocked on their gasoline.
 
#18 ·
My dealer kerbecks filled my tank with plus 89 octane when I picked up the z. I saw this as they filled and asked about it and was told that plus was fine to use. After reading the manual. Cover to cover, it's states that engine damage can occur with less octane. Not happy about this at all. Contacting gm this morning.
 
#21 ·
You will not have done any engine damage running 89 octane. The CPU will adjust to that octane just fine. You do however sacrifice some mpg at the lower octane. No reason to contact GM.
 
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#19 ·
I drove my 1997 C5 172,500 before I traded it in on the C7.
Only used regular fuel all that time. Never had an engine problem. Used Mobil 1, and sometimes went 6-8000 miles before oil change. Burned 1/2 quart every 2000 miles. Engine was perfect when sold.
On C7 I've used regular, but usually fill up with medium grade. Not even sure what octane that is, as it will vary with dealer.
But I have to add this...I never tromp on the throttle. Car has enough latent power that you don't have to. IF I were on the track, yes, I'd use the highest octane possible.
On a trip back from Florida in the C7, over a distance of 270 miles @ 62 mph average, my fuel was 35.1 mpg, and that was with the AC on.
Quite possible that with a higher octane it might have been a tad higher, but I'm satisfied.
 
#20 ·
The time when an engine demands the greatest octane from a fuel is when it is being loaded hard, regardless of speed. During break in, you are supposed to avoid heavy engine loads. So the 89 will be fine, but when you refuel, put in the recommended fuel.
 
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