Nitrogen offers no significant plus in tires

Dear Bob: I recently bought four tires at a local vendor, and they now have a policy of putting nitrogen into the tires instead of regular compressed air.

They claim that the nitrogen holds up better with temperature changes and road conditions. I have not noticed a difference between the two.

The problem is that, when I do have to bring the tires up to the proper pressure, nitrogen is not something that you find at the local service station.

Any opinion?

— No Name, via e-mail

A: Nitrogen, a colorless, odorless and tasteless gaseous element, makes up about 78 percent, by volume, of the earth’s entire atmosphere. Oxygen, another colorless, odorless and tasteless gaseous element, accounts for 21 percent. Other rare gases make up the remaining 1 percent. This is what you get when you fill your tires at the local service station.

I talked to the people at Michelin, and they told me that nitrogen, for the most part, offers no significant advantage over regular air. The reason it is used by some tire dealers, such as yours, is that it tends to hold up slightly better over time, and can keep tires from losing pressure quite as fast as they would if normal air were used. That advantage is only a slight one, however, especially if you check your tire pressure every few weeks.

As far as keeping your nitrogen-filled tires up to snuff, it’s fine to simply add normal air to the nitrogen — after all, as we have seen, normal air is itself 78 percent nitrogen. Of course the nitrogen will be diluted ever so slightly each time you add air. But that’s nothing to worry about, because we have been driving with air-filled tires ever since the first pneumatic was invented.

And remember, we breathe this stuff each and every minute of our lives. If it’s good enough for our bodies, seems like it should be good enough for our tires.

Dear Bob: We have a 1994 Buick Roadmaster Estate Wagon, and when I turn off the motor a fan under the hood continues to run. Several times I have gone out of the house and heard the fan running. If I get into the vehicle, start it up and then turn it off, the fan stops running.

I have never had another vehicle that did this. What can I do to fix the problem?

— C.C., Newburg, Pa.

A: This may not actually be a problem at all — it might very well be perfectly normal operation.

The electric cooling fan is supposed to run awhile after the car is shut down to help cool the engine, especially during warmer weather. You don’t say whether this happens in warm weather, cold weather or both, but if it’s happening in warm weather after the car has had a good run, it’s probably normal for the fan to run for five or 10 minutes after shut-off to help provide cool-down protection.

After this period, of course, the fan should shut off automatically. If the fan continues to run for, say, half an hour or longer, then obviously something is awry, probably in the fan switch. Have a shop check the unit and, if necessary, replace the switch.

Dear Bob: Would you print the e-mail address to obtain the current government Fuel Economy Guide?

— J.D., Dallas, Texas

A: You can download a copy of the 2005 Fuel Economy Guide, a very useful reference for anyone considering buying a new car, at www.fueleconomy.gov. For a printed copy, e-mail a request to fueleconomy@ornl.gov or write to NREL Fuel Economy Guide Request, 1617 Cole Blvd., M.S. 1633, Golden, CO 80401.

AMERICAN DRIVERS FIGHT BACK

Here’s a tip that will help you get better gas mileage while fighting terrorism and cutting our nation’s dependence on Mideastern oil:

This gas-saving driving technique is one you can benefit from a thousand times each year. When approaching a stop sign where cars are already stopped in front of you, slow down to allow the other cars to pass through the stop sign before you reach it.

If you don’t adopt this technique, you’ll often have to stop several times at each stop sign, stopping when you reach the end of the line, pulling forward as the first car leaves, stopping a second time, pulling forward again as the second car leaves and so on. Slow, stop-and-go driving eats gas, and you’d be surprised how much you can waste at stop signs.

If you plan ahead by even a few seconds, though, you can minimize the wasted gas, stopping only once when traffic permits and at all other times avoiding an extra stop or two each time out. You’ll be calmer and less frustrated … and you’ll save gas and money as well.