Beware the Bench Test

In case any of you are celebrating the Imperial Depression of 2009 the way I am -- that is, by keeping a beater running -- watch out for your buddies at Auto Zone, Advance Auto Parts, and so on. A few weeks ago, the starter in my 1992 Mercury Topaz ceased working. I didn't have time to fool with the thing then, as I was busy closing out Physics 219, so I parked it and hopped into my much-less-fuel-efficient backup ride: my 1992 Ford F150 longbed pickup truck. Gas isn't super-expensive at the moment, but I am an engineer and I do hate waste, so I was anxious to get my economical little rustbox back on the road. Pulled the starter out of it, and took it to the Auto Zone where it was purchased (lifetime warranty!), and they of course tested it ... and it tested "good." Hmmmmmm, thought I. I don't think the poor underpaid counter guy at Auto Zone was cheating me, but they do have a financial interest in the starter being good (they don't have to replace it for free). So, I went down the street to Advance, where they have the opposite incentive -- if it tests bad, they presumably sell me a replacement. It tested good there, too.

So, the starter and I went home, where I reinstalled it in the vehicle. Maybe the battery was bad ... I could check that by swapping it for the truck's battery, and I did, and it still wouldn't start the car. Cables, maybe, although they looked fine. At least, they looked fine until I removed the positive cable, one more time, and the battery-terminal clamp on the end of the cable cracked. So I now needed to replace it anyway; $14.30 later, I did. The negative cable I simply removed and showed it to my multimeter, which reported its resistance as zero. No surprise there; it looked fine, as I said. The new positive cable, on being installed, made no difference. Still no starter function. The starter relay? Clicking away just fine when the key was turned, and shorting across its terminals with the classic screwdriver made no difference; it was good. So I brooded for a day. (Well, I did some yard work while I brooded, and I took my daughter to a par-three course for nine holes of pseudogolf. You see, I've been around for a few years now, and I think I know a bad starter when I'm up against one, and that starter was BAD. Still, it's hard to pull the trigger on a part that'll set you back almost a hundred bucks for a rebuilt, when everybody who tests it says it's good.

But, I was getting extremely tired of playing with the thing, and I was out of alternatives. So, Sunday afternoon, I bought a starter. An hour and a half later -- it worked perfectly. My former starter may have tested "good" in the bench test fixture, but it certainly tested "bad" under the car, bolted to the bellhousing. And today, Auto Zone got it back after all. And I can now get the starter in and out of the Topaz really quickly, what with all the practice I've had lately. Still, it cost me the skin off the first knuckle of my right pinkie-finger, and several bitter profanities, and too much of my time.

So, as I say: take those bench test results with a grain -- no, make that multiple grains -- of salt.