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What about oil changes?

September 8, 2011 - Larry DeHays

How often should you have your car's oil changed, and what kind of oil should you use? Good questions, and the very definite, absdolutely firm answer is......"It varies". Not very helpful, I know. Here's the scoop. The reasons oil is changed is twofold; because it gets dirty and because it wears out, or looses its' viscosity. How quickly this happens depends almost entirely on the type of driving it has been subjected to. Car manufacturers give a recommended schedule for "normal" driving and another interval for "severe" driving. Severe duty is defined by them as operation in high or low temperatures, dusty air, or stop and go traffic. In other words, normal driving is defined as a steady speed on clean interstate highways in moderate temperatures. So unless your driving is strictly interstate, you fall under the "severe" condition.

The usual interval recommended is 5,000 miles for "normal" driving, and 3,000 for severe. The average american drives 1,000 per month, so every three months is about right for oil changes. If you drive less than that, you might think you can stretch out the interval, but here's the kicker. The primary reason to change it is contamination, and that happens with time, even without driving. Water, gasoline, ozone, sand, metal shavings and more accumulate in the oil over time. Three months are usually enough. The second reason for changing oil, (wearing out) simply doesn't happen. Modern oil is tougher than it used to be. It has to be changed because the contamination harms the engine. An old machinist once explained to me that inside an engine, all those moving metal parts never touch one another. They are all separated by a thin film of oil, so you can appreciate how important that oil is.

That brings us to our final subject, the type of oil to use. Synthetic oils are getting popular, and recommended for some high-end cars, like new Corvettes. Its' main advantage is that it's tougher than mineral oil, and better able to handle temperature extremes. However it costs much more to buy. Synthetics do a better job of protecting your engine, but remembert that contamination is the primary problem, and both oils contaminate at the same rate, so don't be tempted to keep it in longer because it is so pricey. Doing so will eliminate the advantage of using it.

Larry DeHays is the owner of DeHays Automotive, Inc. of Fort Myers Beach, an A.S.E. certified automobile Technician, and an arbitrator with the Florida Lemon Law Program.


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