Q: I purchased a new car with nitrogen-filled tires as part of the dealer's accessory kit. The next morning after driving the car home I checked the tire pressures. All four tires measured 37 psi. The door-jamb tire information placard states the front tires' pressure should be 32 psi and the rear 30 psi. I lowered the pressures to the specified amounts.

I understand nitrogen is not subject to temperature changes. A few days later we had a cold snap and I re-checked the pressures and found them to be down about 1 to 2 psi. Is there any way of checking to make sure there is really nitrogen in my tires?

A: When you bled down the pressures, did you laugh uncontrollably? Oh, wait, that would be nitrous oxide, not pure nitrogen. And by the way, no one said nitrogen was not sensitive to temperature changes, just less so than good ol' air.

Typically, a colored valve stem cap is used to identify tires filled with nitrogen.

I do not know of any kind of physical or chemical test to prove nitrogen is the gas in your tires, but you could try a relatively simple experiment. If your new car came equipped with a full-size spare tire, fully deflate it to expel any nitrogen, then fill it to the same cold pressure as your car's tires. Every six months check the pressure in the spare tire. If the pressure is measurably lower than the vehicle's tires, the car's tires are filled with nitrogen.

Anyone else know of a method to confirm nitrogen in a tire?

Q: I own a 2012 Volvo S60 with 36,000 miles and a 2005 Jaguar XK8 with 65,000 miles. Both have ZF automatic transmissions which are supposed to not need to be flushed or otherwise maintained. The Volvo's manual says not to change the engine coolant. I don't drive either one hard and haven't had problems. What do you think about the no-maintenance instructions?

A: For your Volvo, you are correct that Volvo has no service recommendation for coolant changes. And under "normal" driving, and no recommendation for routine transmission service as well. But I did find a note in my ALLDATA automotive database that Volvo does recommend transmission service every 52,000 miles if the vehicle is used for towing or if a message appears on the dash. Turning to your Jaguar, I find no service recommendation for the transmission although, like your Volvo, it's fitted with both a drain and fill plug for servicing.

Both carmakers suggest brake fluid replacement every two years, and Jaguar would like you to change the coolant every five years.

All I can tell you is that despite my difficulty accepting these no- or long-interval transmission service recommendations, I do recognize significant improvement in lubricants used in modern automatics. Many carmakers and oil companies develop specific lubes for use in their engines and transmissions. Ditto coolants.

My problem is that I cannot fathom how the additive packages blended into these lubricants and coolants will not degrade, oxidize or be consumed over 100,000-plus miles and many years of driving.


Motoring note — In regards to the 2006 Mazda Tribune that the key fob would not unlock the doors nor start the car, here's a possibility I hadn't thought of. Thanks to Janice Wilson for this: "I too had issues with my Mazda CX7 remote sometimes not working and then it would — very annoying. Do you know what it was? It happened when the remote and my cellphone were beside each other in my purse! Never happened since I have different spots for each of them now."

Dang cellphones. Not only a dangerous distraction, but an evil electronic jamming device. Who knew?