Q: This has been bugging me too long. The first time I heard about nitrogen in tires I thought it was a joke. When I saw the $10 per tire I was charged WITHOUT my prior OK, that did it. Someone came up with this gimmick to make money and I think it's a scam. Air already has 70 percent nitrogen — I'm good with that. Tell us what you think.
A: Don't sugarcoat it, now. I do think that charging 10 bucks per tire for a nitrogen fill is a bit steep, but there are benefits to filling tires with this inert gas. Granted, nitrogen makes up 78 percent of the air we breathe, but the remaining components — oxygen, carbon dioxide and moisture — aren't of any real value in pressurizing our tires. In fact, oxygen and moisture can be detrimental, leading to deterioration of the rubber and corrosion of the wheels. And due to the moisture content, temperature changes lead to larger changes in tire pressures. Any tire used in any type of performance scenario will benefit from 100 percent nitrogen primarily due to more stable pressures, more predictable pressure changes and less heat build-up.
Pure nitrogen does cost more than plain air. Suppliers and shops must buy and maintain systems to create and dispense pressurized nitrogen. Is it worth the extra cost for our mundane daily drivers? Unless it's free or costs just a buck or two per tire when new tires are mounted and you're willing to add only pure nitrogen when necessary, probably not. Most shops install nice bright-colored valve stem caps when filling a new tire with nitrogen as a reminder. Adding plain old air to a nitrogen-filled tire negates the benefit of the original nitrogen fill.
I look at nitrogen sort of like rustproofing — it can be of benefit, but only if you maintain it regularly.
Q: We have a 2002 Saturn LW300 that is well-maintained and has almost 61,000 miles. Our shop says that because of the age, the spark plugs should be changed even though they are rated for 120,000 miles. The car runs well. Any comments or opinions would be much appreciated.
A: My ALLDATA automotive database shows a 100,000-mile replacement interval for spark plugs on your vehicle. Thus I don't think replacement at just over 60,000 miles is necessary, nor advisable. Why not advisable? Two factors: cost and potential removal problems.
To replace the spark plugs on Saturn's 3-liter V-6, the intake manifold and ignition modules have to be removed to gain access. The flat rate labor estimate for spark plug replacement is just short of three hours. Access is less time-consuming on the 2.2-liter four-cylinder engine but the ignition module must still be removed.
Here's my main concern — getting the old spark plugs out without damage to the threads in the aluminum cylinder heads. After 13 years and 60K miles, there's a significant chance of electrolysis and corrosion between the steel plug threads and the aluminum threads in the head. Removing a "stuck plug" can easily damage or destroy the aluminum threads, leading to potentially expensive repairs.
