This new puzzler is gonna be better than last week's crummy puzzler. I'm not sure it qualifies for greatness status. But it is better than last week's puzzler.

Okay, here it is. Not an original puzzler. This didn't happen to me, but it is still good.

Here it is;

My friend drives an '83 Toyota Tercel. She took it to a mechanic because it was overheating. The mechanic checked it all out and he replaced the radiator. The entire radiator. But this made the problem worse. The car was still overheating. Replaced the radiator and it overheats more. This is intriguing.

She returned the car to the mechanic. He and all of his co-workers, not just one or two, but all of them were completely baffled. They stood around while the car was running, smoking cigarettes, and drinking coffee, which is what mechanics do when they can't figure out the problem. They do that little mechanic shrug, smoke a cigarette, and drink coffee. They were trying to figure out what was wrong. 

Suddenly, one mechanic exclaimed, "Ah ha! I've got it!"

What did he see? 

The hint is, of course, that there was nothing wrong with the new radiator. There was, however, something wrong with the old one and they did well to replace the old radiator. 
But that mechanic saw something while he was sitting there smoking a cigarette that told him what was wrong.

What was wrong? What did the mechanic see?

Good luck!