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Q: I understand that the composition of gasoline is adjusted seasonally ("summer blend" and "winter blend") due to EPA requirements. Given that many people are driving less during the pandemic, what would be the effect on drivability if you filled your tank shortly before the market switched over to the summer blend and you ended up driving with winter blend deep into the summer? Likewise, what about the converse situation into the winter season?

A: This is a timely question because the switch to summer blend is about to happen. Winter blend gasoline has a higher Reid vapor pressure (RVP) to make the engine start easier. The fuel vaporizes at a lower temperature. The RVP generally is 15. In the summer, RVP is usually 7. Running winter blend gas in warm weather can cause engine performance problems such as stumbling and, occasionally, stalling. Winter blends also evaporate quicker in the summer, contributing to ozone issues and smog.

Gas stations typically make the switch to summer blend on or near June 1. Even if you need only a half-tank or less, fill up with summer blend as soon as it's convenient. You don't need to worry about this as much the other way around. When it gets cold in fall, summer blends create less of a problem.

Don't shoot

Q: Back in the "old days" when we had to buy an aftermarket GPS that sat on the dashboard, we were cautioned that thieves could break into the car while we were at the movies or sporting events. They could steal the GPS, push "HOME," drive to our house and steal our stuff at their leisure. My GPS never was stolen, but just in case, I had programmed in the address of a neighbor who was a firearms dealer. He, his wife and daughter carried weapons with them at all times. It would have been a rude greeting for someone breaking into their house.

A: I hope you cleared this with your neighbor first.

Don't guess at repair

Q: The fuel economy of my 2005 Subaru Outback 3.0-liter, 6-cylinder with 151,000 miles went from the low 20s to not even in the teens. Shade tree mechanic friends are telling me it is the O2 sensor. I'll need about $800 in parts alone to replace four sensors. The Subaru dealer says it's not the sensors because the check engine light isn't on. They are suggesting a tuneup, which will cost $400. The spark plugs are the originals, which means they're 16 years old with 151,000 miles on them. Could getting new plugs really double my gas mileage?

A: The dealer is correct that even one bad O2 sensor out of the four would trigger the check engine light. But it sounds like they are guessing by suggesting a tuneup. I have a hunch it would not help that much. Find a technician who knows how to analyze what he sees on a scan tool.

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