Today: The Bouncing Fender Test

Dear Car Talk

Dear Car Talk | Feb 03, 2015

Dear Car Talk:

I went to one of those "drive in for an oil change" places. Almost immediately after arriving, the young man started mashing down repeatedly on the fender above the left front wheel of my van. Then he told me that because the car kept bouncing after he stopped mashing on the fender, I need new struts. He said he also noticed an oil leak coming from my strut, which is more evidence that the struts are shot. Do struts really have oil in them? Wouldn't I have noticed extra bouncing when driving around? Is this a con?

-- Leisa

That's actually a legitimate test, Leisa. My brother used to do a similar test when he was buying a used car: He would mash down on the fender, and if the fender fell off, he'd know that was the car for him, and he'd make an offer.

When a strut (also called a shock absorber) is working correctly and somebody pushes down hard on one corner of the car, that corner should go down and compress the spring, and then come up once and stop. If it keeps going up and down, then the strut is worn out.

And yes, struts are filled with oil. If this guy noticed some oil on the side of the strut, that's another sign that the strut has failed. You wouldn't notice the leak yourself; it's a small amount of oil that seeps out, not enough to create a puddle in your driveway, or to lease to BP.

And you might notice the extra bouncing when you drive, but you might not. You know the story about the frog they put in water, and then slowly bring the water to a boil? The idea is that if you had dropped the frog into already-boiling water, of course he'd notice. But because the water heats up gradually, the frog doesn't notice he's being cooked until some foodie is putting extra-virgin olive oil on his legs and tucking in his napkin.

By the way, please don't sic PETA on me, folks. No actual frogs were harmed in any of my analogies.

Anyway, the same can be true of worn-out shocks, faded brakes, scratched-up windshields and live-in mothers-in-law: You don't notice how bad these things have gotten because they get just a little worse every day, over a long period of time.

In any case, I'd suggest that you get a second opinion on the shocks. You clearly don't trust this guy who changed your oil, and you don't have a relationship with the shop. In fact, you're right to be cautious, because there are shops that put mechanics on commission, so they have an incentive to urge you to do additional repairs.

I'd recommend that you either go to your regular mechanic, if you have one, or find one on www.mechanicsfiles.com. That's a database of mechanics personally recommended by your fellow Car Talk readers and listeners.

If a mechanic you trust does the same test and tells you that you need shocks, you can then be pretty sure that the oil-change guy was on the up and up with you.

And if you do need shocks, we recommend that they get replaced in pairs.


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