TOM: Yes. Bring a fresh shirt to change into, Juan. Most waiting rooms are on the petite side.
RAY: If I had to guess, I’d say you’ve lost some refrigerant. The fact that your air conditioner’s performance has degraded so slowly (it changed very little in the past year) suggests that you have a very slow leak.
TOM: In that case, the prudent thing to do would be a vacuum test, to confirm that your leak is very minor. If it is, then you can just get your system recharged — that is, have it filled back up with refrigerant.
RAY: It may be another year, or more, before it gives you problems again. By then, with any luck, your Volvo may be sailing over to Korea as scrap metal, preparing to return to America as a Home Depot chimnea.
TOM: I mean, if you were really environmentally conscientious, you’d ask them to do a dye test to find the leak or, more likely, leaks. And then you’d fix them, no matter what.
RAY: If your system was losing its charge every week, or if your car was much newer, that would be our suggestion, too. And you’d have to do it, or invest in a lot more shirts.
TOM: The reason it’s nice to do the diagnosis is because you may find a relatively simple problem. If your biggest leak is just a cracked hose, for instance, fixing it could cost you as little as $100.
RAY: But if it’s one of the major AC components, that’s more like $1,000. And since you’re driving a 15-year-old car with almost 200,000 miles, I’m guessing you don’t have a lot of extra money to spend.
TOM: In that case, you should do what most of our customers with slow leaks do, and just recharge it. At least see how long the charge lasts. If it lasts only a week, you’ll obviously have to reassess. But if it lasts the summer, it may be the last charge you ever need.
What do gas-enhancement claims really mean?
Dear Tom and Ray:
Is there any merit to the claim that nitrogen in gasoline has any benefit for cleaning the engine? What’s the chemistry behind it? Or is this just the latest gasoline-additive scam? — David
TOM: Hmm. Maybe they’re trying to get rid of all that excess nitrogen that they couldn’t talk people into buying and using in their tires?
RAY: You’re asking about Shell Oil Company’s latest campaign, David, in which it claims that its gasoline is “nitrogen enhanced.” And like most of the “enhancement” offers that come via e-mail these days, David, this claim probably should be ignored.
TOM: Shell claims that its new nitrogen-enhanced gasoline keeps your engine cleaner.
RAY: Here’s the story. Every gasoline is required to use a certain minimum amount of deposit-control additive — which does help keep deposits from forming on your valves and other engine components. All of these additives contain small amounts of nitrogen.
TOM: But nitrogen is only one of several ingredients in these cleaning additives. So my guess is, Shell has increased the amount of cleaning additive in its gasoline, which has “enhanced” the nitrogen component.
RAY: And more cleaning additive is good. I mean, why not? It’s such a small amount of nitrogen, compared with the volume of gasoline, that it doesn’t affect the amount of nitrous oxides that come out of the tailpipe. And if your engine runs cleaner, then all the better.
TOM: But what the claim “nitrogen-enhanced” doesn’t tell you is how much additive the gasoline had in the first place, and how much it has now. Maybe Shell used to add the absolute minimum necessary? Maybe it already was good, and got better? There’s no way for us to know, as these are trade secrets. And by claiming its gasoline is enhanced, all we know is Shell is using more now than it was before.
RAY: Right. It would be like me and my brother claiming that our newspaper column is now “enhanced with right answers.” It could mean that we really are trying harder and putting more time into answering each question. Or it could mean that we’ve enhanced the column to the point that we now get at least one answer right a year.
Send your comments or questions for Tom and Ray to: Car Talk Plaza, P.O. Box 3500 Harvard Square, Cambridge, MA 02238. Listen to them Saturdays at 10 a.m. on 91.3 FM or 88.5 FM. Visit them on the Internet at www.cartalk.com.
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