Question: I have, perhaps naively, been flummoxed for some time over the fact that my cars all “require” gasoline rated 87, but, whereas 87 is the regular gasoline sold in most states I have visited, in New Mexico regular is 86 and “plus” is 88. Therefore, I am always buying the intermediate grade of gas, as at least one local auto tech has told me the lower grade will cause knocking, especially at this elevation. Would you be so kind as to explain what’s really going on and whether you think there is a sufficient difference to justify the “plus” grade? And, why don’t N.M. gas stations offer the 87 rating as regular? Thanks. — David Burling

Answer: You raise a good point, David, about fuel grades and what should be used in your car. I have to say, the advice you were given was pretty much dead-on. If your car requires 87, you need to use 87 or higher to avoid detonation (pinging). Granted, newer cars have built-in sensors to monitor detonation and make adjustments to reduce it. The only problem is they’re reducing the power of the car — that is, if everything in the system is working properly.

If you are light on the pedal, you probably will not experience much detonation or feel the power loss. However, if you find yourself quite familiar with the lower half of your throttle pedal, you will want to meet the manufacturer’s minimum requirements for the octane rating. Something to consider is that a smooth-running engine with the proper fuel is actually burning fuel smoothly in the combustion chamber. When it detonates, there is actually an uncontrolled explosion blasting the inside your engine. This can lead to costly engine damage (check out the piston below).

You also bring up a good point on the mysterious 86-octane rated gasoline. This fuel is specially blended for the Rocky Mountain region because of our higher elevation (it comes as low as 85 octane). Since we are higher up in elevation, we have less atmospheric pressure. So, essentially your car has less outside force pushing air into your engine’s combustion chamber.

In turn, this causes less compression, and with less compression you don’t need as high of an octane fuel to prevent detonation inside your engine. (This does NOT apply to cars with forced induction like turbochargers or superchargers since they actually produce pressures well over atmospheric.)

So, does this mean you don’t need a higher octane rating of fuel? Personally, I would still stick with what the manufacturer recommends. My reasoning is that, with higher elevation, we also have those things that make the elevation higher still: mountains. When climbing them, we are placing a high demand on the engine, and you will want things operating as efficiently as possible.

In the end, it is just a few more dollars for the right fuel for the car. There might be a chance you could get away with a lower octane rating, but it would all be for nothing if your engine is damaged by detonation.

One other tip on fuel: You will want to use Top Tier fuels in your car to keep the buildup of deposits to a minimum. Those are offered by basically all the top-brand fuel stations around town (see www.toptiergas.com for specific providers). Personally, I avoid all “discount” fuel stations for my car. Plenty of the running problems I encounter at my job can be attributed to this special low-priced fuel.

Jason Dickman is an ASE and a Saab Master Technician and works at Don Chalmers Saab in Santa Fe.

Learn basic auto knowledge at SFCC

Does the thought of changing your spare tire scare you? How about buying or selling a used car?

If so, there is a class designed just for you: Automobile Empowerment will be held Sept. 29 at Santa Fe Community College. Instructor Jason Dickman has more than 14 years of professional experience as an auto technician. He is ASE and Saab Master Certified and writes for Drive.

The class will cover:

• Changing your spare tire,
• Locating and changing a fuse,
• Maintenance like changing light bulbs and wiper blades,
• Buying and selling a used car,
• How to jump-start a car,
• Items you need in your car,
• Plus a plethora of car tips not commonly thought about.

To sign up, call 428-1270 and ask for the continuing-education class Automobile Empowerment, LS390. Cost is only $29.