My car manufacturer calls for 91 octane gas but my local pump only has 89 and 92.

Dear Tom and Ray:

I recently purchased an 8-cylinder Lincoln LS. 91-octane fuel is recommended. My local gas stations carry 87, 89 and 92. What should I do? -- Rex

RAY: Well, my brother can get 91 octane near his house, so he suggests that you just give him the car and go buy yourself something cheaper that runs on 87 octane, like a nice Hyundai.

TOM: Not to worry, Rex. The simplest thing to do is to use the 92. You'll be wasting a little money and creating a little extra pollution, but the car will run fine on 92, and absolutely no harm will come to it.

RAY: If you want to be more economically sensitive (i.e. cheap), you can mix the 92 and the 89. If you put in two-thirds of a tank of 92 and a third of 89, you'll create your own 91-octane.

TOM: And don't worry about being absolutely perfect every time. This car, like most modern cars, has a knock sensor that keeps the engine from knocking itself into oblivion when the octane's too low. So the car can handle an occasional tank of lower-than-recommended octane gas without damage.
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