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Mid-grade gasoline (89)

Old 01-16-2018, 03:33 PM
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Default Mid-grade gasoline (89)

Dawned on me today, WHY? What is the purpose of the mid grade octane gasoline? I get the "Regular" which is an economy product and good for most all engines and of course "Premium" for engines that demand a better product.

Seems like a waste of storage to me, who buys the mid grade? We have 2 cars that require premium and everything else gets regular (lawn equip/atvs get Rec90 due to low use).

It has to be a marketing or stocking scheme used by stations.
Old 01-16-2018, 03:41 PM
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Originally Posted by Mersiles View Post
Dawned on me today, WHY? What is the purpose of the mid grade octane gasoline? I get the "Regular" which is an economy product and good for most all engines and of course "Premium" for engines that demand a better product.

Seems like a waste of storage to me, who buys the mid grade? We have 2 cars that require premium and everything else gets regular (lawn equip/atvs get Rec90 due to low use).

It has to be a marketing or stocking scheme used by stations.
My understanding is that 89 is just a 50/50 mix of 87 and 91, so no additional storage needed.
Old 01-16-2018, 03:55 PM
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I've driven cars that "require premium" for decades. I always used mid-grade, with zero problems.

Given the price of mid vs. premium, I'm probably ahead by several thousand dollars by now.
Old 01-16-2018, 03:58 PM
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I'm grateful for mid-grade. My Stihl lawn equipment and classic car were designed for 89 octane fuel.
Old 01-16-2018, 04:26 PM
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A common misconception is that using premium (91/93 octane) fuel is better for the vehicle. It isn't like conventional vs synthetic oil.

Engines that require premium fuel run better on it because the engine is tuned for it. They usually have higher compression that requires higher octane so there isn't detonation in the cylinders.

Running high octane fuel in an engine that doesn't require it is a waste in most cases, except maybe while towing.

And, as stated above, mid grade is mixed at the pump from the premium and regular tanks. There is not separate store for mid grade. I find that older carburetor and TBI engines run better on mid grade.
Old 01-16-2018, 04:32 PM
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Correct, higher octane isn't inherently better. Octane is just resistance to ignition, so higher octane fuels are harder to burn. Lower octane fuel should actually burn more efficiently. High performance engines that compress more air into tighter spaces (like high compression ratios or forced induction) or have more spark advance need the fuel to resist igniting before the spark occurs (or to slow the flame front after spark occurs), which is why they require higher octane fuel. Putting 91 octane fuel into an engine that's designed for 87 is a waste of money. On the other hand, most modern engines that are tuned for higher octane will compensate for lower octane fuel by retarding the spark advance when they detect knock, at the expense of power output.
Old 01-16-2018, 04:36 PM
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Most modern engines recommending or "requiring" premium gas will run just fine and adjust themselves to mid-grade. The savings isn't directly proportional usually, as mileage tends to be better when run on premium. Learned this from my last three cars which all spec'd premium gas.
Edit: Thunder I see we were simul-posting there.
Old 01-16-2018, 04:37 PM
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My grandpa's Volvo was required to be ran on premium octane if he put 87 in it it would ping it's ass off. There is a need for it.
Old 01-16-2018, 05:15 PM
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Some stuff actually calls for 89 octane or higher. My truck (2008 Hemi Ram) says it’s recomended. Regarding storage, most stations have a 87 and 93 octane tank, and blend on site. Some stations have a seporate tank.

Also a lot of small engine equipment calls for 89 of higher.
Old 01-16-2018, 05:23 PM
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F200XB calls for 89. All my still equipment calls for 89. My truck is currently tuned for 89.

I run 93 in the boat as it give a little leeway in degradation if it sits for a little bit
Old 01-17-2018, 05:30 AM
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Originally Posted by thunder550 View Post
My understanding is that 89 is just a 50/50 mix of 87 and 91, so no additional storage needed.
In most areas, mid-grade is 1 part 93 octane and 2 parts 87 octane (there is no mid grade tank except at marinas, which usually just carry mid-grade), and sells for about 2/3 of the difference between regular and premium - it is the most profitable gas a retailer sells.
Old 01-17-2018, 06:13 AM
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A little off topic if i may. Don't see it much down here in Florida, but out west (specifically South Dakota where my summer home is) gas stations vary on what they carry. Some (maybe even most) have non-ethanol in 91 octane as well as ethanol, others offer 85 octane, with ethanol. My Tahoe is 'Flexfuel' but I have yet to run it on anything but 87 regular ethanol, wonder what it would run like with the 85, it's a good bit cheaper than the 87.
Old 01-17-2018, 06:26 AM
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Aren't the octane levels there lower due to elevation? I've noticed that when out west above 4k feet or so. Regular is 85, mid is 87 and premium is 89 or 91.
Old 01-17-2018, 06:35 AM
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Originally Posted by JKBrad View Post
Aren't the octane levels there lower due to elevation? I've noticed that when out west above 4k feet or so. Regular is 85, mid is 87 and premium is 89 or 91.
At higher elevation, air pressure is lower so there's less air that makes it into the cylinder on the intake stroke. The ECM compensates by injecting less fuel. When the piston compresses the mix, the overall pressure is lower inside so less prone to preignition, so lower octane fuel is acceptable.
Old 01-17-2018, 06:37 AM
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Originally Posted by LI32 View Post
In most areas, mid-grade is 1 part 93 octane and 2 parts 87 octane (there is no mid grade tank except at marinas, which usually just carry mid-grade), and sells for about 2/3 of the difference between regular and premium - it is the most profitable gas a retailer sells.
Makes sense. Here in AZ our high grade is 91 instead of 93, so the ratio is probably different with 91/87 than with 93/87.
Old 01-17-2018, 06:39 AM
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I often wonder if anyone actually buys those other grade fuels.
Old 01-17-2018, 07:07 AM
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so, I understand the octane levels, but does the quality of the fuel vary much from station to station?
Old 01-17-2018, 07:12 AM
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Originally Posted by Jim henscheli View Post
so, I understand the octane levels, but does the quality of the fuel vary much from station to station?
Yes - where you buy fuel matters. There is a branding of fuel called Top Tier (see list below). It is superior in quality.

You want to buy from stations that a) are very active, meaning their fuel supply turns over frequently and b) not fill up when the tanker is there or was just there, it stirs everything up.

http://www.toptiergas.com/

TOP TIER™ Licensed Retail Brands
76
Aloha
Amoco
ARCO
Beacon
BP
Break Time
Cenex
Chevron
Chevron (El Salvador)
Chevron (Guatemala)
Chevron (Honduras)
Chevron (Panama)
CITGO
Conoco
Co-op
Costco Wholesale
Costco Wholesale - Diesel (select locations only)
CountryMark
CountryMark PLUS
Diamond Shamrock
Esso
Express Mart
Exxon
Fast Fuel
Fast Stop - Diesel (select locations only)
Fast Stop Express - Diesel (select locations only)
Hele
HFN - Hawaii Fueling Network
Holiday
Irving Oil
Kirkland Signature Gasoline
Kirkland Signature - Diesel (select locations only)
Kwik Star
Kwik Trip
Kwik Trip Express
Mahalo
Marathon
Metro Petro
MFA
Mobil
Mobil (Canada)
OAAI
Ohana Fuels
Petro-Canada
Phillips 66
PUMA (El Salvador)
PUMA (Panama)
PUMA (Puerto Rico)
QT
QuikTrip
Ranger
Ranger Mustang
Ranger Stallion
Ranger Thoroughbred
Reeder's
Shamrock
Shell
Shell (Canada)
Shell (Puerto Rico)
Shell Nitrogen Enriched (Canada)
Shell V-Power (Canada)
Shell V-Power (Puerto Rico)
Shell V-Power NiTRO+ (Puerto Rico)
Shell V-Power NiTRO+ Premium (Canada)
Sinclair
Sunoco
SuperAmerica
SuperFuels
Tempo (Canada)
Texaco
Texaco (El Salvador)
Texaco (Guatemala)
Texaco (Honduras)
Texaco (Panama)
Tri-Par Qwik Stop
Valero
Win Win
Old 01-17-2018, 08:00 AM
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Older cars would ping when run on low grade. Then again, it was easy enough to move the timing to compensate.

I did careful experiments on my old Dodge van (1983?). I got 10% lower mileage on Super vs. Regular .
Old 01-17-2018, 08:11 AM
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Originally Posted by Afishinado View Post
A little off topic if i may. Don't see it much down here in Florida, but out west (specifically South Dakota where my summer home is) gas stations vary on what they carry. Some (maybe even most) have non-ethanol in 91 octane as well as ethanol, others offer 85 octane, with ethanol. My Tahoe is 'Flexfuel' but I have yet to run it on anything but 87 regular ethanol, wonder what it would run like with the 85, it's a good bit cheaper than the 87.
Altitude makes the difference. Less air, lower the compression is.

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