My 2002 Honda Odyssey (96,000 miles) has been a great car, other than having to replace the transmission at 60,000. When we take a road trip, we notice that after about two hours on the highway, the floor of the car just behind the front passenger seat gets hot — really hot! So hot that it is uncomfortable to keep shod feet on the carpet for more than a few minutes! The underside of the right, middle-row seat gets uncomfortably hot to the touch, too. We took the car in to our regular mechanic, who generally does a good job. He said that everything is fine as long as nothing is glowing under the car when it gets that hot. It’s hard to believe that this is not a fire risk! I’m not confident I would be able to see something glow in broad daylight. Do I listen to my mechanic, or do I cave to my safety-freak maternal instincts and take this in to the dealer for what is likely to be an overpriced repair bill, whether or not they fix the problem? What do you think is causing this? Many thanks.

TOM: It sounds like the heat is coming from a catalytic converter. There’s one right in the spot you describe.

RAY: It may be something minor, like a missing heat shield. Or it could be something more significant. But it was lame of your mechanic to send you on your way without bothering to figure out what’s wrong.

TOM: So you have two problems: A heat problem, and a mechanic problem. If you don’t feel that your mechanic is willing to put in the time to figure this out, then find someone else (check the Mechanics Files at for a free list of highly recommended mechanics by ZIP code). Because, of course excessive heat can be a fire hazard.

RAY: There are three possibilities that come to mind. The simplest is that a heat shield has corroded and fallen off. Parts that get very hot, like catalytic converters, are surrounded by shielding material to prevent the heat from igniting something nearby. Like your buttocks.

TOM: But heat shields are made of cheap metal, and eventually they fall off, or start making so much rattling noise that people remove them. So first you want to see if your heat shield is intact.

RAY: The second possibility is that something’s wrong with the engine that’s causing your converter to run hot. If your fuel-air mixture is too rich — due to a cylinder misfire, for instance — gasoline will get combusted in the converter instead of in the engine. And that can produce a lot of heat — which you will feel, whether the heat shield is intact or not.

TOM: The final possibility is that your converter is plugged up. That’s what happens when converters get old. Typically, you’ll notice a drop in power because exhaust is unable to leave the engine freely, but you might not notice it. A plugged converter will run hot, and eventually glow.

RAY: Whatever it is, though, get it figured out and address it. Or your next letter to us might start out: “My 2002 Honda Odyssey has been a great car, other than having to replace the transmission at 60,000 and the four-alarm car fire at 97,000!” Good luck.

You were answering a question a few weeks ago about what type of oil to use (5W-30, 10W-40, etc.). My question is: What does the “W” mean? For years, I understood it to mean “weight.” But then I read some literature published by Shell Oil Co. stating that the “W” meant “winter,” and that “weight” was a misnomer. So, what is your take on this? Thanks!

RAY: It’s “winter.” Oil’s viscosity — or thickness — is described as an oil’s “weight,” so that’s probably why there’s confusion about what the “W” means.

TOM: According to the American Petroleum Institute, which is sort of the Vatican of oil, when you see a designation that reads, for instance, 5W-20, it means that the oil acts like 20-weight oil in the summer — or, generally, in hot weather. And it acts like a lighter, 5-weight oil in the winter, or in cold weather.

RAY: Now, since you’re an inquisitive fellow, you probably want to know why it’s not labeled “5W-20S,” then?

TOM: Because the “summer” designation is unnecessary. Obviously, if one number is the cold-weather number, the other must be for hot weather. It’s why boxes sometimes say “This side up” but don’t bother also saying “This side down.”

RAY: Wouldn’t it be more useful if boxes DID say “This side down” or “Other side up,” instead of “This side up”? I mean, once you can see the words “This side up,” you already have that side up! What you really need is “Other side up” to tell you when the genuine 4th-century Ming vase you bought on eBay for $49 is upside down and already broken.

TOM: Have we answered the question?

RAY: I think so. I mean, I’m sure you understand why we have multi-viscosity oil. In the old days, people had to drain out their summer-weight oil in the fall and put in winter-weight oil. That was a pain in the butt.

TOM: But when it’s winter, you want a lighter oil so the engine’s parts can move through it more easily. In the winter, everything’s harder to move.

RAY: Like me, for instance.

TOM: So now, oils miraculously (I think) vary their viscosity to adapt to conditions, so we can spend our time more productively, like surfing eBay for more junk.

Got a question about cars? Write to Click and Clack in care of this newspaper, or email them by visiting the Car Talk website at