As a follow-up to my column regarding nitrogen use in tires, this from John MacBain, Ph.D.:
"Nitrogen obeys the same universal gas law as oxygen, hydrogen, and every other gas known to man. Both nitrogen-filled tires and air-filled tires will show exactly and precisely the same pressure sensitivity to ambient temperature changes. As to comparing the tires on the vehicle to the spare to see which if any are nitrogen-filled, this too fails for the same reason plus an additional reason. The tires on the vehicle will lose a small amount of air during normal driving beyond the amount lost by the spare due to flexing of the tires against the rims and the flexing of the rubber itself. About the only advantage that actually accrues is that nitrogen may leak out of a tire more slowly as the molecule size is physically larger than that of oxygen and most other components of air. But since air is 78 percent nitrogen, the net advantage even on this score is minimal at best. The nitrogen "advantage" is a ridiculous hoax stemming from the fact that Indycars and other racers fill their tires with nitrogen.
The truth is that these racing circuits use nitrogen in their tires not because of any vehicular advantage of doing such. They need pressurized nitrogen in the pits for other purposes, and using that pressurized nitrogen source for tires as well simplifies their lives by requiring only one pressurized gas source rather than having pressurized air as well. I appreciate your consideration. Please stamp out this ridiculous theory and be part of the solution in educating your readers. If you want further concurrence, please consult with any physicist or mechanical engineer at the U of M."
A: Having been a racer for four decades, I would say you could not be more mistaken. I can assure you that nitrogen is not used to fill race tires just as a convenience. If there were no reason to use nitrogen in tires, why would racers pay the extra cost for nitrogen versus compressed air that works very nicely for air wrenches, air jacks, etc.? The prime benefit of nitrogen is more predictable and stable tire pressures under racing conditions. Pure nitrogen is moisture-free. Since race tire temperatures often exceed the 212 degree F. boiling point of water, moisture vaporizing inside the tire would play havoc with tire pressures, a huge factor in light of the fact that a one-half pound change in tire pressure can significantly affect the handling of a 3,400-pound NASCAR stock car.
In regard to the validity of comparing nitrogen-filled tires to the air-filled spare, you correctly identified the precise benefit — less pressure loss in nitrogen-filled tires due to the larger size of nitrogen molecules. And of course, the lack of moisture in nitrogen reduces the potential for wheel corrosion.
"Hoax"? I think not. Granted, the benefits of nitrogen in tires are small, but very real. I can't help but wonder who the physicists or mechanical engineers would concur with. Academia vs. real world? I'll take real world any day.
Q: I have a 2010 Grand Caravan. At a recent oil change after 3,000 miles the engine was a quart low. There is no sign of a leak, blow-by or excessive exhaust. The service folks indicated that Chrysler calls this normal and acceptable. Can this be true?
A: Yes. Oil is consumed in the act of lubricating cylinder walls and valve stems. Normal assembly tolerances will allow a small amount of oil to remain on the cylinder walls and valve stems, where it will burn. Normal wear and tear, perhaps a bit more. Most manufacturers do not consider oil consumption a concern until it exceeds one quart per thousand miles. Unless there is a significant change in the rate of oil consumption, I wouldn't worry.
To put oil consumption in perspective, an engine that burned one drop of oil per cylinder per power cycle would consume a quart of oil in roughly four miles.