I'll bet most Autoblog readers take pretty good care of their cars. And like me, I'll bet most of you change your oil about every 3,000 miles or so.
But recently I got to wondering whether that's the right thing to do. After all, most automakers recommend far more extended intervals, usually around 7,500 miles. And with oil prices skyrocketing, I thought it might be a good idea to start following the owner's manual. But I wasn't really sure.

After all, over the years I've heard lots of different opinions on how often you should change your oil. Mechanics and oil companies say you should stick to the 3,000 mile interval, while automakers say most people don't need to change it that often. The synthetic oil people say you can even take it to 25,000 miles.

Obviously, they all have their own vested interest. If you're selling oil or oil changes, you want people changing their oil as frequently as possible. If you're selling cars, you'd like to see them wear out so people have to buy new ones. If you're selling synthetics you want to be able to charge a lot. So who should you believe? I decided I needed to hear first-hand from both sides, the auto industry and the oil industry.

John McElroy is host of the TV program "Autoline Detroit". Every week he brings his unique insights as an auto industry insider to Autoblog readers. Follow the jump to finish reading this week's editorial.

The oil guys tell me an oil change is an awfully cheap insurance policy for your engine. They admit that following the owner's manual is the proper thing to do, unless you do severe driving. But they have a pretty broad definition of what they consider "severe." Their definition includes driving in very cold or very hot weather, in dusty conditions, any fast acceleration, stop-and-go driving, long highway hauls, or doing any amount of towing. In other words, they think most people engage in severe driving.

The car guys, on the other hand, tell me that 3,000 mile intervals went out with hula-hoops. They say that made sense way back in the 1960's when carburetors let a lot of unburned gas get into the oil. But with fuel injection, much tighter engine tolerances, extremely strict emissions standards and with much better engine oil than was available 40 years ago, most of them have more than doubled that interval. And yet, they admit that interval varies with the type of engine in a car and how it's driven.

That's why a number of automakers use oil monitoring systems in their engines to tell the driver when to change the oil. These systems look at how many times the engine is started, how high it revs and how hot it runs. Some systems, like BMW's, actually measure the quality of the oil. Others, like GM's, use an algorithm to calculate when the oil needs changing. Thanks to this system GM says that most of its customers now change their oil at 8,500 miles instead of the recommended 7,500.

But it varies. A Chevrolet Trailblazer with the 4.2 liter I-6 is seeing oil change intervals of 12,000 to 13,000 miles, GM says. But the same vehicle with the 5.3 liter V8 typically needs an oil change at 7,000 miles. That's mainly because the I-6 has a big oil pan and takes 7 quarts of oil, versus 6 for the V8.

All this can have a huge impact on how much engine oil we use. Americans buy 1.1 billion gallons of engine oil a year. Using the automakers' suggested interval could put a big dent in that number. And yet, to put it in perspective, we burn about 420 million gallons of oil a day in the form of gasoline and diesel fuel. So our engine oil usage represents less than 3 days of fuel.

But it can have an enormous environmental impact. Even though most engine oil now gets recycled, the EPA says that 185 million gallons of it gets dumped on the ground, tossed in the trash, or poured down the drain. That translates into the equivalent of 17 Exxon Valdez oil spills every year.

But back to my dilemma. My car doesn't have an oil monitor so what should I do? Stick with what I've been doing and change the oil every 3,000 miles? Or do what the manual says and change it at 7,500? I think I'll compromise and bump it up to 5,000 miles-even though I can already hear my mechanic yelling about what an idiot I am.

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