A reminder: Click and Clack's Great Unyielding Truth

Dear Car Talk

Dear Car Talk | Jun 01, 1991

Dear Tom and Ray:

I am the proud owner of a red, 1990 Mazda Miata. Wanting to keep it in good shape forever, I need your help. The owner's manual says the gasoline octane I use should be 87. Where I live many of the major brand, regular unleaded gasolines are rated at 86. If I'm not aware of any engine knock, do I run any risk in using 86 octane? Can I safely save a little money on gas after spending all that money for the car?

TOM: Lewis, don't you remember the famous Click and Clack Great Unyielding Truth? "It's the Stingy Person who Spends the Most." You just spent 15,000 dollars on a great new sports car. Now you're trying to save a few bucks a year on gas. C'mon, Lew! Get a life!

RAY: You should always use a detergent gasoline with the exact octane recommended in your owners manual; no higher and no lower. Lots of people think that using a higher octane does the car a favor, but it actually tends to be a waste of money and a source of increased pollution.

TOM: And you shouldn't go below the minimum, because that can make the engine "knock." Knocking is what you get when you have small, unwanted early explosions inside the cylinders. Even though you say you're not aware of any knocking, it could be there.

RAY: Even worse, Lewis, some of the real cheap gasolines don't have enough detergents in them. Over time, that could cause your fuel injectors to plug up.

TOM: So if you really want to keep this Miata forever, don't be a cheapskate. Fol??low the manufacturers instructions and use 87 octane. But on the other hand, if you bought this Miata because it was always your dream to have an MG, keep using the 86. Once the fuel injectors get plugged up and the knocking takes its toll, this Miata will run just like an MGB!

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