QDear Tom and Ray:

One of the exhaust heat shields fell off my Honda Civic Hatchback (2001) awhile ago. The dealer told me not to bother putting it back on or replacing it, because I don't need it anyway. (1) Why does Honda (or any manufacturer) install the dang things if all they do is rattle and fall off? (B) After the heat shield had been gone for nearly a year, my exhaust manifold cracked. Could the missing heat shield have hastened the failure of the manifold? -- Holly

ATOM: To answer your second question first, the heat shield had nothing to do with the cracked manifold. So forget about that. The heat shields are actually metal guards that surround the various pieces of your exhaust system. They're there to shield other stuff from the excessive heat given off by the exhaust.

RAY: There are top and bottom shields. The bottom shields are there so that if you park on tall, dry grass or some other combustible material, your 600-degree exhaust system won't set stuff under the car on fire. It doesn't happen often, but it can. And when it does, it's very exciting!

TOM: On top, the heat shield prevents the heat of the exhaust from going upward, toward the floor of your car. And depending on which piece of the heat shield is missing, that could cause the bushings in your shifter to dry out, or the bottom of your sneakers to melt and become one with the carpet.

RAY: The heat shield is made up of a bunch of cheap, thin pieces of sheet metal that are welded in place. And since they're all under the car and constantly exposed to the elements, they're particularly vulnerable to rusting and breaking loose.

TOM: Our lawyers tell us that we must always replace rattling or missing pieces of the heat shield. Why? Because they say they're already too busy defending us against libel lawsuits from the carmakers.

RAY: But we know there are lots of people who choose not to replace the heat shield. It can cost 20 bucks to just tear it off, versus maybe $200 to install a new one -- if you can even buy the piece you need individually.

TOM: And your dealer may know -- based on the area in which you live, the kind of driving you do or your preference for asbestos-toed shoes -- that your car may be fine without one particular piece of the heat shield. If you're not permanently melted to the floor of the car, write back in a few years and let us know if he was right.

Dear Tom and Ray:

I took my car to a mechanic friend of mine. I talked to him at 11 a.m., and he said that he already had eight hours' labor in the job. I said: "What? You started at 3 a.m.?" Then he said that time is not billed out based on actual clock time, but on what "the book" says is required. He said if you're fast, you can make more money, but if you're slow, you lose money, so it comes out even. Is this common procedure, or is he a weasel? Just checking! -- JJ

TOM: The book your friend was referring to is the "flat rate book," put out by one of several independent companies like Chiltons, All-Data, Mitchells or Motor's. The book lists -- based on surveys and what manufacturers pay for warranty work -- a reasonable number of labor hours that it should take for an average technician to complete a job.

RAY: So if a guy is learning a job on your car, and it takes him all day, you won't have to pay for all the time he's walking around scratching his head.

TOM: And the book rate rewards the guy (like your friend) who has done the job before, remembers which wrenches he needs, and doesn't need to keep referring to the repair manual.

Got a question about cars? Write to Click and Clack in care of The Post, or e-mail them by visiting the Car Talk Web site at www.cartalk.com.

(c) 2005 by Tom and Ray Magliozzi

and Doug Berman