RAY: Hi, we're back. You're listening to Car Talk with us, Click and Clack, the Tappet brothers, and we're here to talk about cars, car repair, and the answer to last week's automotive puzzler. This was a good one, man.
TOM: This was a good one man.
RAY: Well, I don't know how good it was, but it was at least interesting.
TOM: Yeah.
RAY: Anyway, a customer brought his car to us a few weeks ago, and he had all kinds of problems for us to solve, as is always the case. But none of them was quite as good as this one.
TOM: Well, you know the truth is this is an automotive puzzler, but you don't have to have any automotive knowledge in order to figure it out.
RAY: Not exactly. I should have said that last week.
TOM: That's what's nice about it.
RAY: Anyway, one of the problems he had is that the cooling fan was running all the time, and that's not supposed to happen. Most cars, at least modern cars, have electric cooling fans that are operated by a thermostatic switch. So when the temperature of the engine gets to a certain point, a switch and a relay turn on the fan and then when it cools down, the switch and the relay shut off the fan. But this guy's fan never shut off, even when the car was first started in the morning. When the engine was ice cold, that fan came right on and stayed on until he shut off the engine. So we open the hood, and we're looking around, and it didn't take long to figure out that someone had actually hotwired the fan. It turned out that the fan relay was bad, and rather than fix that, the mechanic, I suspect, merely took a piece of jumper wire, spliced one end to a hot ignition wire and the other end to the fan. And the result was that whenever the ignition was on, and that wire was hot, the fan was on. So I find this jumper wire and because it was attached so poorly, I just yank it off and, of course, as soon as I do this, the fan loses its power supply and it starts to slow down. Now, I don't know what possessed me to do this next thing, but while the fan is slowing down, I take this wire in my hand and I touch it to a ground under the hood, and I get a spark. And I say, "Huh. That can't be right." So I hook it back up again, and, of course, as you would expect, the fan springs to life. It's roaring away and again, I disconnect it. The fan begins to slow down, and again, I touch the wire to ground, and again, I get a spark. So I do what any good scientist would do, I jumped to a conclusion.
TOM: Just like the spark jumped to the wire.
RAY: I say, "Ah hah!" And in my "Ah hah!" moment, I also solve another problem that the car has. And it's this. If you were running the engine and you turned the key off and even removed it from the ignition lock and put it in your pocket, the engine would continue to run for sometimes four, five, six seconds and then would finally shut off. So the question is what's going on here?
TOM: Wow, this is soŠ
RAY: And Tommy's right. You didn't need to know a whole lot about, or anything maybe about, cars, but when I pulled that wire off --
TOM: All you needed to know was Faraday.
RAY: Yeah, and we're going to get letters from all the engineers in the group, who are going to say that this can't happen.
TOM: Oh yeah, we'll say. Oh yeah.
RAY: Just like they all said, you can't have a DC motor that runs backwards, if you change the poles, which is not true either. We know that. But what happened when I disconnected that wire is the fan didn't just stop turning it immediately, it was slowing down, but it was still, like any fan that's unplugged, it continues to turn. While it was turning, it was acting as a generator.
TOM: Of course.
RAY: And it was making electricity, hence the spark. And it also explained why when I turned the key off, the thing didn't shut off right away, because, believe it or not, the electric fan's spinning now. Even though the key is off and there's no power being supplied to the fan, the fan is supplying electricity, which is running the car's ignition system.
TOM: Isn't this sweet?
RAY: And as the fan slows down, the engine begins to stumble and miss and finally, the fan is going too slowly to supply enough current to keep the engine running, and the thing --
TOM: Wow.
RAY: -- stops running.
TOM: What a beautiful puzzler.
RAY: Do we have a winner this week?
TOM: Do we ever. The winner this week is Michael Faraday.
RAY: From jolly old England.
TOM: No, the winner is Christina Stolberg from Denver, Colorado. And for having her answer selected at random from the gym bag full of correct answers that we got, Christina will get a $25 gift certificate to the Shameless Commerce Division at the Car Talk section of cars.com. And with that gift certificate, she can get a copy of our new music CD, "Car Talk, Car Tunes."
RAY: Really, you don't --
TOM: Lucky you.
RAY: I think we really struck the right balance with this album.
TOM: What? The right balance between music and us?
RAY: Yeah, exactly. All music and no us. Anyway, we'll have a brand new matchstick puzzler.
TOM: Oh, the matchstick series.
RAY: So get 16 matchsticks ready and we'll be back with that puzzler in the third half of the show, so stay tuned. In the meantime, if you have a question about your car, or anything else, please give us a call at 888-CARTALK, which is also 888-227-8255. Hello, you're on Car Talk.
[ Car Talk Puzzler ]
