New muffler and exhaust pipe, $400. New tires, $700. Third trip to find out why the “check engine” light is still on, $150. The mechanic is thinking the engine may need a head gasket. Estimate: $1,200. Trade-in value on old clunker? Priceless, in the sense that it has no value at all, not in the sense that it is worth a lot.

How do you decide when to trade in a car? Maybe I’ve made all the repairs and it will run for another 98,000 miles. Or maybe this is just the beginning, and it will need the new head gasket and then a new transmission and then a new radiator, and then the generator will go out before the thing stops running altogether.

I’ll never be able to sell it with that check-engine light on. The good news is that sometimes it goes off. Maybe I’ll get lucky and the light will be off when I try to trade in the car. Would that be wrong? After all, it has a new muffler and new tires; someone would be getting a practically new car.

Why do I have to go through this every six or seven years?

”Because you’re too cheap to buy something new,” says Sue. I’m sure she meant to say “thrifty” or “value-conscious,” and it just came out wrong. Why buy something new when you can get almost the same car for much less if you let someone else drive it around for five or six years to get the kinks out?

”You’re just buying someone else’s problems,” she says. One of the problems that came with my car was a stain in the backseat that has a remarkable resemblance to the Shroud of Turin. It must have been there when I bought it, but it has slowly become more visible over the years. Is it a miracle, or did someone spill bleach back there? I say it’s sun damage; Sue’s theory is that someone died back there and the body wasn’t found for several weeks, which is why I was able to buy the car so cheap.