Motor Mouth: Tire tread penny test now costs a quarter

Q: I've heard people talk about doing the penny test on your tires to determine if they have enough tread depth. Would you please explain what that means?

A: The space between the edge of a penny and the top of President Lincoln's head is 2/32 of an inch. (Math purists, please don't write me a nasty letter. I know that is 1/16 of an inch, but tire treads are measured in 32nds.) If you can see the top of Lincoln's head, your tread depth is less than 2/32 of an inch and it's time to replace your tires.

At least, that's the old standard. Lately, the advice is to use a quarter. If the tread touches President Washington's head, you have at least 4/32 of an inch of tread remaining, Goodyear says.

Q: Both of my Toyotas will take an extra gallon or more after the gas pump first cuts off. To fill my 2016 Toyota Sienna requires me to wait about five seconds after gas pumps cut off and then open the pump handle just a little bit. I have never had any problem with filling them up to the top, but I have heard that is not a good idea.

What is the downside of doing this?

A: Pumping more gas after the nozzle has clicked off runs the risk of allowing fuel to get into the evaporative emissions control charcoal canister. It is very expensive to replace. Sure, you might be able to squeeze in a few more miles between fill-ups, but it's not worth it.

Q: The service manual for my vehicle indicates that I should replace the brake fluid every three years. I have not found any technician or knowledgeable vehicle service person who can tell me why I need to do it that often. At the dealer when they wanted to do this, I asked why in this age of advanced technology, Honda couldn't make oil capable of lasting more than three years. They did not answer but simply skipped this step. Am I risking damaging something?

A: Brake fluid is a glycol-based compound. It is hygroscopic — it attracts water. Water boils at a much lower temperature than brake fluid, and that can cause brake fade. Plus, the water vaporizes, and, as you know, a gas can be compressed. That's not good in a hydraulic system. And if that's not enough reason, water in the system can damage some components. You need not change it at exactly 1,095 days, but do so regularly.

Q: After using Rain-X on my windshield, even new wipers leave streaks. How do I remove the Rain-X?

A: A mixture of equal parts water and white vinegar will work. Once you have the glass squeaky clean, polish it with a dry terry cloth towel or, better yet, a microfiber towel.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to motormouth.tribune@gmail.com.