The Morning Call (Sunday)

Don’t top off your gas tank

- Bob Weber Send questions along with name and town to motormouth.tribune@gmail.com.

Q: My wife owns a 1999 Subaru Forrester. Recently, we smelled gas after her gas purchase, and, after some conversati­on, she decided it was best to stop when the nozzle automatica­lly shuts off. No more topping off. The problem is that after her last gasoline purchase, when she drove away, she saw that her tank was only ¾ full. Do you have any recommenda­tion for being certain her tank gets a true fill-up while not suffering any bad results from topping off?

— M.S., St. Charles, Illinois A: Squeezing that last drop of gas into the tank is a bad idea. It is a throwback to when most people paid with cash and tried to avoid getting weird change. Check your owner’s manual for the tank capacity. With that you can extrapolat­e the amount pumped versus the gauge reading after the fill up. The gauge may be off.

Q: In Bob Weber’s response to a question spark plug replacemen­t, he mentioned the problem only occurring on the Ford Navistar engine. I am a Navistar employee and all engines sold to Ford were diesel engines which do not have spark plugs.

This response implied that our engine had an issue that could not be true. In a future column, I would appreciate a

correction made. — Deborah Shust, Navistar

A: Right you are. I mistakenly wrote Navistar engine when I meant to say Triton engine. The spark plug removal issue was common with the three-valve Triton V-8 engine in the late 1990s and early 2010s. Good catch.

Q: I enjoy your articles including the one today having to do with poverty inspiring learning about repairing cars. That certainly was the case for me. Acouple of weeks ago you discussed a problem having to do with battery voltage and commented

that 12.2 volts would indicate a fully charged battery. But a battery at 12.2 volts is at about 50%, while a fully charged battery will show 12.6 volts.

— D.K., Chicago

A: Right again. Automotive batteries have six cells (connected in series) having 6.1 volts per cell when fully charged. By the way, at 11 volts the battery is considered too dead to start the car.

Q: Your answer to the question about the freezing of pure water and pure ethylene glycol is flawed by one word. Your statement said “when mixed they react

forming different molecules. This is not what happens. What does happen is that when mixed they interact causing a freezing point decrease and a boiling point increase. Principall­y this is caused by the individual molecules of water and ethylene glycol being separated from one another. The result is that they cannot easily form the necessary molecular interactio­n to allow crystal formation. It would surprise me greatly if the explanatio­n from Prestone did not use the term interact rather than react. I suspect that you will hear a similar explanatio­n from

chemists around the country. Thank you for your interestin­g column. As a former “car nut” in high school, I still enjoy stories about cars and especially about engines.

— Paul Holm (chemist and professor, retired)

A: Thanks, Paul. When I read your message, I remembered that mixtures can be separated physically, but compounds chemically. Coolant is a mixture of antifreeze and water. I will be glad to see 2020 fade from my rearview mirror.

 ??  ?? Squeezing that last drop of gas into the tank is a bad idea. It is a throwback to when most people paid with cash and tried to avoid getting weird change. Check your owner’s manual for the tank capacity.
Squeezing that last drop of gas into the tank is a bad idea. It is a throwback to when most people paid with cash and tried to avoid getting weird change. Check your owner’s manual for the tank capacity.
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