QUESTION: A couple months ago I had a seizure. An MRI found a nonmalignant tumor, and the operation a month later was a success. But because of the seizure, my driver’s license was revoked for six months until they see if I will have a recurrence of the seizure.

From time to time a friend or relative will drive one of our two cars — a 2005 Dodge Caravan and a 2010 Volkswagen diesel Jetta — but the cars can sit for days or even weeks without being driven. Both do start up immediately when called to service.

I’m sure other people have cars they may not use for short or long periods of time. What precautions do you suggest? Should I start the cars and just let them idle once a week?

—Craig

ANSWER: Congratulations on your medical recovery. It sounds like the usage of your two cars is working out OK; the batteries holding up and they are getting some usage, which is better than none. My only concern is the fuel becoming stale.

Vehicles parked more than three weeks at a time can benefit from the use of a plug-in float charger or solar panel, if parked in adequate sun. A float charger is a smart trickle charger that provides just enough battery charge to offset parasitic losses while the vehicle sits. These run from $10 to about $20. Both take just a moment to hook up and plug in to a typical wall outlet. If the car isn’t near an electrical outlet but can be parked so the windshield sees six or more hours of direct sun, a 1.5-watt solar panel, about 6 inches by 15 inches in size, about $20, should adequately do the job. Larger 5-watt panels, about $50, work better but should be used with a charge controller —which runs about $10-$15 — to avoid overcharging the battery. Both sizes are widely available.

Gasoline begins to go stale in a little over a month, and I’d recommend treating what’s in the two tanks with some Sta-Bil fuel treatment. If either of the vehicles is unused for more than a month, it’s not a bad idea to run the engine perhaps 15 minutes and drive back and forth a bit in the driveway to exercise the brakes. Be sure to check tire pressure before anyone takes either vehicle out on the road.

Q: Your columns have proven useful, but we, and possibly others, are confused as to whether we should use miles, time or some combination to schedule maintenance, especially of various fluids. We have a 6-year-old Toyota Tacoma with 31,000 miles and a 5-year-old Toyota Avalon with 21,000 miles. We change oil and filter every 6 months, usually with less than 3 thousand miles. If the other older folks are anything like our friends, there are many with this question.

A: I believe miles are more important than months, and it’s the kind of miles that really matter. If your trips are of less than a half-hour of mostly continuous run time, I’d stick with the every-six-month regimen. If most trips involve greater than a half-hour run time, which allows the engine to fully warm up and boil off contaminants from the motor oil, I’d feel comfortable stretching the time to 12 months between oil changes. Take a look at the inside of the oil filler cap. If the bottom of the cap shows more than a little milky residue or moisture, shorten the oil change intervals.