Lower Octane in Cold Weather
Lower Octane in Cold Weather
The purpose of octane is to prevent premature detonation in the engine's cylinders. Using a lower octane than recommended (required) causes the knock sensors to kick in and retard ignition reducing power and any economies gained by using cheaper fuel. Would it be possible to switch to mid level octane gas during cold weather because lower air temps reduce the risk of knock and the resultant engine performance? If it were possible to use cheaper fuel, that would mean my next DIY oil change would be 50% underwritten by the savings or does the colder air not really do much to counter knock?
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The gas stations don't cheat the Marketteers/branders cheat since all gasoline in a particular area is the same and the minute amount of differential additives can't do much.
The problem with displayed pump octane is you don't know how they arrive at the average.........the cheap way with higher Research octane or the expensive way with higher Motor octane formulas. Lots depends on the newness of the column catalyst bed and how much the refinery is pushing it!
Each engine is different plus mileage and wear and dirty injectors so all you can do is try an 89 octane if successful then you pray that the next tankful is the same...........once its in, its too late! No amount of any aftermarket octane booster will get it back to 93 octane!
800 gallons per year [15 k miles] x 10 cents is $80 per year insignificant when compared to the other $2,000-$2,500 the Q cost to maintain and repair each year [tires, brakes, fluids, repairs].
If a few hundred or even a thousand per year is critical to your living standard you are definitely driving the wrong car!
The problem with displayed pump octane is you don't know how they arrive at the average.........the cheap way with higher Research octane or the expensive way with higher Motor octane formulas. Lots depends on the newness of the column catalyst bed and how much the refinery is pushing it!
Each engine is different plus mileage and wear and dirty injectors so all you can do is try an 89 octane if successful then you pray that the next tankful is the same...........once its in, its too late! No amount of any aftermarket octane booster will get it back to 93 octane!
800 gallons per year [15 k miles] x 10 cents is $80 per year insignificant when compared to the other $2,000-$2,500 the Q cost to maintain and repair each year [tires, brakes, fluids, repairs].
If a few hundred or even a thousand per year is critical to your living standard you are definitely driving the wrong car!
Quote »
If a few hundred or even a thousand per year is critical to your living standard you are definitely driving the wrong car! [/quote]
Always looking at ways of improving efficiency and economy.
So, in a best case scenario with good quality mid grade fuel, a nominally performing engine and air temps below 20F, engine performance would remain close to that of higher octane levels since knock is not an issue?
If a few hundred or even a thousand per year is critical to your living standard you are definitely driving the wrong car! [/quote]
Always looking at ways of improving efficiency and economy.
So, in a best case scenario with good quality mid grade fuel, a nominally performing engine and air temps below 20F, engine performance would remain close to that of higher octane levels since knock is not an issue?
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
By the way they reduce REAL octane based on altitude. Jacksonville gas vs Atlanta gas vs say Asheville gas as the air density drops 3.3%/6.6% so does the internal peak pressure by roughly the same amount and HP/torque declines the same amount assumming equal air temperatures.
But sometimes all that is available in the pipeline is good gasoline and as much as they wished it was cheaper they are stuck with paying a penny extra!
Actually Ethanol is very high octane [but 10% x 15 points is only 1.5 points for the mixture and they use cheapo regular to blend so even though the octane say 91 the motor octane is lower than non oxygenated and there is the [5%] mileage penalty to contend with.
But sometimes all that is available in the pipeline is good gasoline and as much as they wished it was cheaper they are stuck with paying a penny extra!
Actually Ethanol is very high octane [but 10% x 15 points is only 1.5 points for the mixture and they use cheapo regular to blend so even though the octane say 91 the motor octane is lower than non oxygenated and there is the [5%] mileage penalty to contend with.