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Dear Tom and Ray: 

My dad owns an old 1969 Ford Mustang and regularly stuffs mothballs in the tank to increase octane or whatever. I drive the car every day, and I notice a sweet-smelling but strong odor enveloping the interior whenever the car is on. It's strong enough to linger on my clothes. Could I be exposed to dangerous levels of naphthalene? – Bart 

TOM: Well, look on the bright side, Bart – I'll bet none of your driving sweaters have holes in them. 

RAY: Actually, the first thing you should do is check for an exhaust leak. If exhaust IS coming into the passenger compartment, that would be very dangerous. But this doesn't sound like exhaust, because exhaust odor is rarely described as "sweet." 

TOM: The next thing to consider is an antifreeze leak, which does smell "sweet." Antifreeze could be leaking from the heater core under the dashboard. And that's not very good for you, either. 

RAY: You could have a mechanic pressure-test the cooling system to check for a heater-core leak.  

And if that's the problem, the heater core can simply be taken out of the circuit or replaced. 

TOM: As for the mothballs, you can tell your father that all we can say in their favor is that we've never seen a moth chew a hole in a gas tank. 

RAY: Some years ago, we asked the illustrious Dr. Jim Davis, Ph.D., director of the chemistry labs here at Car Talk Plaza, about mothballs as a fuel additive.  

And after wasting most of a National Institutes of Health grant thinking about it, he concluded that they do nothing to improve performance. 

TOM: Last time we checked, there were several different types of mothballs on the market. Both WILL burn, so you will get some power out of them. But since mothballs are more expensive than gasoline, this is not a very economical way to get to work. 

RAY: If there were some magical performance-enhancing mothball, Jim says, don't you think Exxon and Mobil would be selling it to us as an expensive gasoline additive, i.e. "Mobil Super ... Now with Mothballs!"? 

TOM: The kind of mothball you mention, Bart, is made of naphthalene, which is a hydrocarbon, like gasoline. For those chemical engineers reading today, it's C10H8, and it looks like two benzene rings fused together.  

Jim says that benzene makes a very smoky fire when burned, so his guess is that naphthalene would make a lousy gasoline.  

On the other hand, he says, since it's just carbon and hydrogen (like gasoline), naphthalene probably wouldn't do any harm to the engine, either. 

RAY: Another type of mothball that COULD potentially hurt things is made of dichlorobenzene.  

That won't improve your car's performance, either, but since it throws chlorine into the mix, it can produce HCl as a byproduct when burned. 

TOM: For those of you who don't remember your high-school chemistry, HCl is hydrochloric acid, the stuff that burns through almost anything it touches. And pumping HCl through your engine and exhaust system is probably not very good for its longevity. 

RAY: Not to mention what it does to the people who happen to be breathing that exhaust. 

TOM: So, tell your Dad to ixnay the mothballs,  

Bart. And have your mechanic rule out an exhaust leak. But then definitely have him check for a coolant leak, because I think that's your problem.  

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