Fact or fiction: Diesel is less polluting than gasoline.

Dear Car Talk

Dear Car Talk | Mar 01, 1998

Dear Tom and Ray:

My husband is buying a new Ford pickup. He wants to buy a diesel engine because
he says it's more fuel-efficient, will last longer, and is less polluting than
gas. I don't know about the first two, but I find the last argument hard to
believe, especially since diesel fuel stinks so badly. Can you clear the air for
me? -- Alice

RAY: I don't believe for a second that he's interested in reducing global
pollution either, Alice. We both know he just wants a big, honking truck. But
we'll address the pollution issue anyway.

TOM: It's somewhat complicated. Diesel fuel is just one step more refined than
primordial ooze. In fact, you can usually see mud, sticks and leaves in it as
you pour it into your car. But since diesels operate at a much higher
temperature than gas engines, some types of pollutants are reduced. For
instance, diesels produce half as much carbon monoxide as gasoline engines.

RAY: On the other hand, diesels produce twice as much hydrocarbon emissions,
four times as many nitrous oxides and five times as much particulate matter (a k
a soot).

TOM: In their favor, however, diesels do seem to deteriorate less (in terms of
how much they pollute) over time. So while gasoline engines pollute
significantly more as they get older, diesel engines start out bad, but, in
their defense, don't get much worse.

RAY: That's what my mother says when she's asked to praise my brother.

TOM: But despite that, I still come down firmly against diesels. As the owner of
a convertible (a '63 Dodge Dart), to me there's nothing worse than driving
behind one of those stinky, disgusting, particulate-belching ash cans. Actually,
there is something worse: getting stuck in traffic behind one!

RAY: And I share my brother's bias. Not because I drive convertibles, but
because I do occasionally drive with my window rolled down.

TOM: And as I said, cutting down on pollution has nothing to do with why your
husband wants a diesel, Alice. He has MDE; Male Diesel Envy. Diesel engines
appeal to guys' "survivalist" instincts. Diesels work by compression only, so
they don't need electricity or spark plugs. Therefore, they -- theoretically --
will still run in the aftermath of a nuclear attack.

RAY: And that's probably what appeals to your husband. After Armageddon, he
thinks he's going to be riding around in this Ford pickup, helping himself to
the latest movies on video (which used to be all gone by the time he got to the
video store, when there were still other people on the planet).

TOM: A lot of diesel engines do last a long time. They are durable, and they do
get pretty good mileage. But they're also noisy, slow, stinky and hard to start
in very cold weather. And, in my opinion, that far outweighs their advantages.
But I can tell you've got no chance of talking him out of it, Alice, so buy
yourself a good set of nose plugs and matching ear plugs -- and good luck.

* * *

RAY: Hey, did you hear that our pamphlet, "Ten Ways You May Be Ruining Your Car
Without Even Knowing It!," is a million seller!

TOM: That's not what I said, you knucklehead. I said I had a million of them in
the cellar!

RAY:Oh. Well, it still has lots of good information on how to make your car last

TOM: Order your copy by sending $3 and a stamped (55 cents), self-addressed,
No.10 envelope to Ruin No.1, PO Box 6420, Riverton, NJ 08077-6420.

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