A rare bird asks how to properly care for a leased car...

Dear Car Talk

Dear Car Talk | Jul 01, 1990

Dear Tom and Ray:

Last June I leased a new 1989 Ford Thunderbird. The owners manual says the oil should be changed at 7,500 and 15,000 miles. Why do so many service shops tell me I should the oil every 3,000 miles or three months, whichever comes first? If I change the oil more often than recommended by the manual, will I do any damage? Mary

TOM: You're a rare bird, Mary. You're the first person who's ever written to us about how to take care of a LEASED car properly! Most people don't do anything to them, and just have them towed back in when the lease expires.

RAY: Anyway, let's start by taking a look at the motivations of the various parties involved here. The manufacturer wants you to think the car is as "maintenance free" as possible. That makes it more attractive to buy. They also know that the effects of not changing the oil don't show up for years, and that you'll probably have sold the car by then. They have nothing to lose by recommending an oil change every 7,500 miles.

TOM: On the other side, you have the service shops. They make money every time you come in for an oil change. They say to change the oil every 3,000 miles (and while you're in, you might as well have your muffler bearings tightened, the air in your tires changed, and your fuzzy dice rotated--all for a nominal charge).

RAY: But in this case, we agree with the service shops. We think that three months or 3,000 miles is the proper interval between oil and filter changes, and here's why. When the oil circulates, it not only lubricates the engine, it also absorbs the dirt and contaminants which result from combustion.

TOM: Eventually, the oil and filter become "saturated", and when that happens, the excess dirt can get between the engine's moving parts and do damage. When you change the oil, you're not only draining out the old dirt that the oil has captured, you are also adding fresh oil which can then absorb and suspend new dirt.

RAY: It's like washing your clothes in the same water for three months. Eventually, the water wouldn't be able to absorb any more dirt, and all of your clothes would turn an Eastern European shade of gray. Changing the water not only gets rid of the old dirt you've just washed out of your clothes, but the new water can then clean more clothes.

TOM: Changing the oil and filter every three months of 3,000 miles is the least expensive insurance you can buy for your engine. Now, if I could only remember to change the wash water that often.

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