Today I was getting gas at Sunoco with my friend when the tank was 1/4 full. He offered to do it for me as I went inside the gas station to buy a coffee. When I came out, to my surprise, he had already pumped 20 Litres of regular 87 octane gas!

When I told him I have been using only 91 octane, my friend (always quick with numbers) quickly calculated that putting another 30 L of 94 octane will get you 50 L of 91. (I later calculated at home that the resulted octane is 91.2 using a linear mixing method). Is this linear calculation correct?

(20L x 87 + 30L x 94) /50 = 91.2

While I was pumping the 94 octane MYSELF, he calculated that he is actually saving me money. The calculated cost of the gas is :

(20L @0.73 cents/litres of 87 + 30L @0.85 of 94 octane ) / 50 = 80.2 cents

While the cost of 91 octane at the pump is 83 cents!

Does this make any sense? I hope mixing octane won't do any damage to the engine.

 

I've mixed octanes myself without any bad effects. To my mind, the results should be identical, provided the proportions are correct.

Your calculations seem to result in a cost saving too.

To do the same mixing at my pumps would not yield the same savings since the higher octanes are proportionately higher in price.

(and we don't often see $.73/l of regular anymore either.)

C.

 

Have no fear. You have done no damage to your car. When driving around home I have been using premium fuel. I take occasional long distance interstate trips and use 87 when I do. The car performs perfectly and my mileage averages about 25mpg cruising at 74mph. Cruising puts only a light load on the engine and 87 works great.
Streaker

 

When you put 87 in the timing in your engine is retarded. Why buy a new performance sports sedan and put 87 in? This isn't a Civic...