Rosalie's got a 10-year-old car with less than 12,000 miles. So, why does she need to change the oil every six months?

Dear Car Talk

Dear Car Talk | Aug 01, 2006

Dear Tom and Ray:

I have a question about cars with VERY low mileage. I have a 10-year-old car that has less than 12,000 miles. What maintenance should I be doing or not doing? I am told at the dealership that, due to the "time" element, I need "flushes" on a routine basis, etc. Is this true? -- Rosalie

TOM: Well, most manufacturers recommend that you change your oil every 7,500 miles. But for you, that would be only once every dog year, Rosalie. There's a "time"-based recommendation as well.

RAY: For most cars that get very little use, the recommendation is to change the oil once every six months. In general, we'd agree with that. Here's why.

TOM: When you run the engine, it produces water. It's one of the products of combustion. Some of that water always ends up in your crankcase, mixed in with the oil. Normally, when the engine gets good and hot, that water evaporates and is expelled by the crankcase ventilation system.

RAY: But if you only take short, little trips -- like two or three miles a day -- you never get the engine hot enough to get rid of that water. So you have watery oil, which doesn't lubricate well.

TOM: So if you take lots of short trips, get your oil changed every six months.

RAY: On the other hand, if you have low mileage because you use the car infrequently, but you really let the engine heat up when you do drive, then you can extend that oil-change interval. For instance, if you drive the car only once a week but drive it 20 miles every time, you're less likely to dilute the oil, so you can change the oil once a year instead.

TOM: As for other stuff, you'll want to change the coolant once every five years or so to renew the rust inhibitors. Those dissipate over time. And you'll need to keep an eye on rubber components, like belts and tires, because those get attacked by ozone whether you use them or not.

RAY: But I wouldn't let the mechanic talk you into too much else. You don't need a transmission service. You don't need a fuel-system cleaning. You probably don't need new brakes. You might need a new air freshener. But the vast majority of cars wear out from use, not from lack of use. So you're doing fine, Rosalie.

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