Don’t waste your money filling tires with pure nitrogen

Q: I recently bought a used 2009 Chevy Cobalt from a local dealer. The tires are filled with nitrogen. I have been given many recommendations on filling the tires. One person told me you can’t mix nitrogen with air (from an air pump at a gas station). Another person said you can. If I can find a tire store that has nitrogen, they charge up to $30 per tire to fill. Can air be mixed with a nitrogen filled tire? — J.B., Allentown, Pa.

A: Air is already 78% nitrogen. It is a mix of oxygen (21%), argon (1%), carbon dioxide (0.04%) and small amounts of several other gases. So, why waste money on pure nitrogen? Use plain air or mix it with the nitrogen in your tires.

Most of the time you can get it for free, or for about a buck at some pumps at gas stations and 7-Elevens.

Q: I upgraded my 20-yearold snow blower to a new model that has an oil reservoir and does not need an oil/gas mixture. I still have 2 gallons of the oil/gas mix left. What is the best way to dispose of this? Could I use it in the new snow blower or my car, or is there somewhere I can take it that would dispose of it? — W.M., Chicago

A: If it is last year’s fuel, you can probably dump it into your car or truck. I have had no problems mixing one part old gas to five parts fresh gas in the tank. You would need at least 10 gallons of fresh gas to dilute the two in the gas can.

Another option is to save it until your community has a hazardous waste collection event. Check with your local authorities for times and locations.

Q: I am one of many people who do not garage their car. When I see a winter storm approaching, I put an old bath towel on my front car window. Voila. When I need to drive my car, I peel off the towel and drive away while others are sitting there scraping away. Is there a better approach than this? —

M.J., Western Springs, Ill.

A: For years I have used an old blanket to get plenty of coverage. I tuck the corners in and close the doors to hold it in place. Recently, however, I have been using a lightweight cover designed especially for the job. It even has magnets in the corners to help retain it. But I always treat the windshield.

Although Rain-X works well, I have discovered that PPG Aquapel lasts longer between treatments, though it costs quite a bit more. I also treat the side and rear window to make ice removal a snap.

Q: How do rain-sensing wipers work? I love mine — it’s like magic! — Susan

A: In most of these systems, a rain sensor is located on the inside the windshield behind the rearview mirror. Infrared light is projected outward through the windshield glass at a 45-degree angle. Depending on how much light reflects back to the sensor (rain, snow or dirt scatters the light, reducing reflect-back), the wipers are turned on at an appropriate speed and delay frequency. Vehicle speed is often another input for automatic wiper operation.

Q: I have a 2018 GMC Sierra 3500 HD with the 6.6-liter diesel engine and Allison transmission. The truck generally gets quite respectable mileage, using about 10-11 liters of diesel per 100 kilometers (22-23 mpg) on the highway. From time to time, though, the fuel consumption abruptly increases from this to 16-17 liters per 100 kilometers (14-15 mpg) for about 20 minutes and then returns to normal. This is on level roads at the same steady speed and wind conditions. Fuel consumption will even remain at 4-5 liters per 100 kilometers (52 mpg) when coasting downhill where it normally drops to near zero. Why does this occur? — Len

A: I believe what you are noticing is the truck is performing an active regeneration procedure, which involves the spraying of additional fuel into the exhaust at certain times to create significant heat so as to burn off accumulated soot (particulate matter) in the diesel particulate filter (DPF).

Duramax and other diesel engines built since 2011 employ a sophisticated and sometimes problematic exhaust emissions treatment system including (from front to rear on Duramax): hydrocarbon injector (HCI), diesel oxidation catalyst (DOC), diesel exhaust fluid (DEF) injector, selective catalyst reduction (SCR) catalyst, and diesel particulate filter (DPF). The parts we’ll focus on are the 9th injector (HCI) and the DPF.

Your diesel particulate filter traps soot and requires periodic cleaning (oxidation) on a regular basis. A combination of heat added due to fuel being injected (about 1,000-1,300 degrees F/538-704 degrees C) and precious metals within the DPF create this reaction.

If the truck is driven on the highway frequently, some soot cleaning occurs naturally (passive regeneration). Active regeneration occurs when the system either senses a level of differential pressure before and after the DPF indicating about 42 grams of soot has built up or 700 miles have accrued since the last active regeneration process.

Raw fuel is injected into the exhaust via the HCI to raise exhaust temperature for a period of approximately 20 minutes, as you have noticed on your fuel consumption readout. Other clues active regeneration is occurring are a different exhaust sound, elevated idle speed, an odor, and more noticeable heat beneath the truck as it is stationary.

Here are three informative articles that help explain this process:

■ https://blog.duramaxtuner.com/blog/how-doesregen-work-in-an-lml-duramax

■ https://www.knowyourparts.com/technicalresources/diesel-engines/ diesel-particulate-filter/

■ http://www.duramaxhub.com/duramax-emissions.html