When to get an oil change.

Dear Car Talk

Dear Car Talk | Dec 01, 1990

Dear Tom and Ray:

I drive very little since retiring, and have put on only 2,300 miles in the last ten months. My owner's manual says to change the oil every 7,500 miles or six months, whichever comes first. But with 5,200 miles to go before I hit 7,500, it seems like a waste of time and money to go in for an oil change. Your opinion, please.

TOM: Well, Irv, there are two basic reasons for changing the oil frequently. The first is that after a certain number of miles, oil starts to lose its lubricity. That's why you change it every 7,500 miles, even if it only takes you a week to drive that much (we actually recommend changing it every 3,000 miles).

RAY: The other reason to change your oil is to get rid of contaminants inside the engine. One of them we call "dirt"--things like metal filings, varnishes, acids, carbon, and sludge.

TOM: Another is water, which is produced by the combustion process. That water mixes with the oil, and except for that extra-strength Perrier you could get with benzine for a limited time last year, we know water is a lousy lubricant. And since you don't drive very much, Irv, you're particularly susceptible to water build-up. Short, infrequent trips never allow the engine get hot enough to vaporize that water so it can escape.

RAY: So the way to get rid of the "dirt" and water is to change the oil. And the reason you should change it every six months is that even if the oil isn't dirty from the mileage, it could be getting "water-logged" from the short trips.

TOM: On the other hand, Irv, you're in kind of a unique position. The negative effects of not changing your oil don't really present themselves until the engine has about 50,000 miles on it. At the rate you're driving, that should be about 25 years from now. So you may want to consider NOT changing the oil. If your car survives, you might end up in Ripley's Believe It Or Not!

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