The Oil Light

Apr 02, 2022

This is a real-life puzzle. We had a fella that came into the shop with an 85 or an 86 Dodge Caravan as luck would have it, with a 2.2. engine. The smallest engine that they make. And he had a bad camshaft and his mechanic had put a new one in there because this other camshaft was made out first.

So instead of having clack, clack, clack, clack, clack, clack, clack, clack, clack from a worn out camshaft, he had a relatively quiet engine. He replaced the camshaft and all of the hydraulic lifters and the rockers rather. Okay, so he had this new camshaft in there, and everything was great. Except that he had a little problem. The oil light was on all the time. So he went back to the mechanic and the mechanic checks the oil pressure and says, "You don't have enough oil pressure. That's why your oil light is on." So he said, "How did that happen?"

Because the oil light had not been on prior. So he said, "Okay, what do I need now? Another 300 bucks for a new oil pump?" And the mechanic says, "Yeah. Debris from the old camshaft must have gotten in there and chewed up the old pump."

And as you might suspect, he did the oil pump did do the oil. So the light didn't remain on, but an interesting thing happened. The light no longer came on ever, even when he turned the key on the on position. But what he didn't notice is that the engine was racing all the time. Oh, that's when he took the car to us, the court of last resort. We had the car for a month and we indeed verify that he had low oil pressure. But interestingly, the light was not on.

Well, we found the light was not going on because it was unplugged. Oh, so we plugged it back in. And lo and behold, the light came on.

The question is what's going on here? The hint is what's going there's nothing wrong with the rest of the motor. The engine is fine. At least, all the parts that could cause oil pressure, are all fine. But! Something else went awry on this job. So what is it?

Now, this is not an easy puzzle. This is tricky. It has to be tricky, because, yeah, we didn't figure it out for a month.


You know what, it's time for the puzzler. And I want to apologize in advance for this puzzler show because I was under pressure.

I was under pressure from the motorheads. (Those are those guys that have all the issues of car and driver in the bathroom and whatever that that really focus on the stuff, really want to get into the engine.) And, and they have been tormenting me with phone calls, saying, "Gee, the puzzles are kind of wimpy. They're math puzzles and grammar puzzles and what kind of non-macho, wimpy stuff is this anyway?"

So last week, I succumbed to the pressure and came up with what my brother called the worst of all possible puzzles (though to be fair, he said that about a lot of the puzzles). So last week, if you remember was about the camshaft on the Caravan. And the question was what, if anything, did the first mechanic do wrong?

Well, what he did was he installed the wrong camshaft, and it had bearing journals that were too small. Although the difference is only a few thousandths of an inch, it was enough to cause a problem. Because of that small difference, it dropped the oil pressure down and made the light come on at idle, and made him think that, in fact, the oil pump was bad.

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