Is it reall possible for a starter to draw 125 AND 400 amps during two different tests?

Dear Car Talk

Dear Car Talk | Sep 01, 1993

Dear Tom and Ray:

I own a 1976 Chrysler Cordoba. My deceased husband was a good mechanic. However, like the proverbial shoemaker never repairing his own shoes, my husband was negligent in doing his own mechnical work. Consequently, the car needed $3,000 worth of work recently. I feel fortunate in having my late husband's boss as my mechanic. He did the work and replaced everything but the starter. Wouldn't you know the starter died a sudden death while he was out of town. I was at the mercy of another mechanic, and had no reason to doubt his ability. But after he put in a rebuilt starter, the car didn't always turn over, and I heard a low growl when I started the car. Later, I asked my regular mechanic to check it out. He said it was drawing 400 amps and suggested I take it back to Mechanic #2. Mechanic #2 also tested it and said it was only drawing 125 amps! But since he also heard the growl, he replaced the starter again at no extra charge. So far, it's been fine. What I want to know is, why would one test show 400 amps, and another show only 125?

RAY: Well, Maridel, it IS possible for a starter to draw a different number of amps at different times. And the number of amps it draws is one of the best ways to tell whether it's working correctly.

TOM: To put it in perspective for you, as a general rule, a four cylinder engine will draw 75 to 100 amps, a six cylinder engine will draw between 100 and 150 amps, and an eight cylinder engine draws 150 to 200 amps.

RAY: You don't say which engine you have in this Cordoba, but you can see that unless your late husband dropped in an engine from a Caterpillar tractor, 400 amps is way too much.

TOM: My guess is the starter's gears are binding up some of the time. When that happens, the starter encounters a lot of resistance, and it tries to overcome that resistance by drawing a lot of amps. This is probably what it was doing when mechanic #1 tested it. That could also explain the growling noise.

RAY: When mechanic #2 tested it, it probably WASN'T binding up, which is why you got a more normal reading.

TOM: We should also mention another possibility, even though it's unlikely in this case. Mechanic #2 may just have been saving face. Mechanics, like fathers, husbands, and boyfriends, hate to admit that they were wrong. So by saying "well, it's drawing the right number of amps, but I'll be a nice guy and replace it anyway," Mechanic #2 gets himself off the hook for not noticing it was defective in the first place.

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