Why can’t pro mechanics loosen up a bit?

Dear Car Talk: I’ve changed my own oil for many years now (less and less as I get older and when the outside temperature is cold). It’s one of the few things I can do anymore. My question: Why do oil places have to tighten the drain bolt and filter so tight? My dad taught me to tighten the drain bolt finger tight and then just a little more; for the oil filter, handtighten it and then turn it another halfturn. I’ve never had either one leak on me. However, when I’m the next one to change my oil after the pros, I have to use a 12-inch pipe as a wrench extender, along with a hammer, to loosen the bolt. I also have to use several varieties of filter wrenches to loosen the filter. Why?

— David

Answer: Well, it could have something to do with your advancing age, David. How often do you have to use that oil-filter wrench these days to open a jar of applesauce?

Actually, the reason those guys tend to overtighten the drain plug and filter is due to painful experience. Several years ago, Rocko the oil-change guy got distracted and let some guy drive away with a loose drain plug. A few days later, the guy was back, demanding that his boss at Pokey Lube pay for his engine — which had seized up. And the boss took it out of Rocko’s paycheck.

So ever since then, Rocko says, “OK, Mr. Funnyman, let’s see you leak oil now!” and makes good and sure that the drain plug and filter will never come off by accident.

Unfortunately, you can do damage by overtightening things, too. If you overtighten the drain plug, you can strip the threads. And while it’s harder to do, you can damage the rubber gasket atop the oil filter if you really overtighten it.

Most likely, though, it’s just going to make it really difficult for the next guy to remove the plug and filter. And I guess Rocko, and his brethren, are counting on someone else being the next guy.

But I don’t think they’re doing it maliciously, David. They’re just erring on the side of too tight rather than too loose.

There is a happy medium, of course. And you’ve come pretty close to identifying it. In the shop, we tighten the oil plug about as much as we tighten a spark plug. I don’t know what that is, but it’s probably in the neighborhood of 20-30 foot-pounds of torque. I’d describe it as “hand tight, plus a little more.”

And for oil filters, we suggest tightening it as tight as you can get it by hand — so you turn it until it stops naturally, and then you might be able to twist it another quarter of a turn.

And if you have to use a 12-inch breaker bar to get it off, then back off a little next time.

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