Under the Hood: What if tire pressure gauges donít agree?

McClatchy-Tribune Information Services

November 27, 2017

Q. I have been working on cars for over 40 years as a hobbyist. I say this to establish that I am not new or inexperienced. My question is this: You have written about and I am a firm believer in maintaining correct tire pressure in vehicles, however, I own at least 3 tire pressure gauges, one an inexpensive pencil type and two dial type both made by reputable companies. None of the gauges provide the same reading. How can I determine which one is right and what assurance do I have that buying an expensive gauge will provide any better results? I look forward to your column every week in the Baton Rouge Advocate.

Johnny Saichuk

A. I feel your pain! The spread on my personal tire gauges is about 4 PSI, which is not acceptable. The best, but not so convenient way to figure out your best one is to see if your local tire shop is willing to check them against their master gauge (if they donít have one of these, shop elsewhere!). Accuracy of pencil type gauges can be improved by applying a shot of WD-40 or similar to the indicator shaft and manually exercising it in and out perhaps 5 times prior to use. My take on the research I did was that dial type analog gauges are usually a better bet than the typical pencil type, with the TireTek premium gauge ($15, calibrated within 2 percent) receiving high marks. Digital gauges appear as good or better than dial gauges for consistent accuracy. One digital brand, Accutire, has highly favorable reviews for accuracy, at a reasonable price ($12-20).

How big a deal is inflation pressure? Under-inflated tires cause sidewall deflection and cause the tire to run at a higher internal temperature. The increased friction also reduces fuel economy by perhaps 5 percent (at 6 PSI low) and reduces steering response and vehicle stability. An increased chance of hydroplaning in wet weather is an additional downside. Over-inflation is a lesser evil but should be avoided also as it reduces the tireís contact patch, leads to a stiff ride and increased tread-center wear, and increases the chance of a tire injury from an abrupt road surface fault. An upside is a slight increase (3 PSI max) in pressure typically enhances steering response. Studies show that perhaps 40-50 percent of the vehicles on the road have one or more underinflated tires and about 20-30 percent have tires that are somewhat overinflated.

Q. My starter groans and moans at times, barely starting the engine. I had the battery tested and it was OK. What else could be causing this? Is it the starter?

Jackie L.

A. Possibly, but tests are needed to be sure. Your battery may be suffering from a parasitic drain (glove box light or similar draining it while parked), itís receiving insufficient charging (a weak or ineffective alternator), or a cable/connection fault at the battery terminals or within the starter circuit. Tests for each of these possibilities are simple and quick for a trained tech to perform. Condemning a weak/faulty starter is easy; if the voltage delivered to and dropped by the starter, while cranking, is within one volt of that measured at the battery (10.5 volts or higher at the starter, 11.5 volts at the battery) poor performance is the starterís fault, not the battery or circuit. A tight engine, due to gummy or thick oil or an internal fault, is also a rare possibility.