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How often/long cars need to be driven

My mom has two vehicles and only drives to grocery store, hair appts,… I know short trips aren’t as good as a few longer trips in. How often should she switch the vehicle she drives. Typically she drives one for about three weeks then uses the other one. What length of time should the vehicle be running to avoid the ill effects of four mile or less trips?

Many short trips and then sitting for weeks is not good on a car either. The cars need the occasional long drive of a half hour or more to evaporate off the water that builds up in the oil, if nothing else.

It really does not matter whether the car sits for 2 or 3, or even 5 weeks weeks; the important thing is to THOROUGHLY WARM IT UP once started. That involves a trip maybe longer than to the hairdresser or the local 7-11.

We lived overseas for 4 years and our two cars were driven by our son every 3 weeks or so. He would use one car either for the weekend or a whole week. The car could sit for a month as long as the battery does not run down.

As mentioned by js, short trips without warmup are killers.

Mom needs to sell one of those cars… Why bear the costs of owning and operating two vehicles??

Honestly I would not worry about it.

These vehicles will lead a long life due to the lack of miles even though harder miles. Just make sure to optimally change oil twice a year otherwise once a year is good.

People overthink this stuff. A car serves you and your life, you do not serve it.

My parents have a 1990 4runner(since new) that is only run twice a year when my dad is home for a total of 500-1000 miles. He started working abroad since 1995. It has 149k and runs perfectly. The only problems have been head gasket but that is a known fault of the V6 engine it has.

My relatives have a 1990 Subaru Legacy AWD wagon with 100k on Nantucket. It leaves the island on occasion but otherwise lives the life of short trips. It has been relatively trouble free even the AWD although it is manual transmission not automatic.

I am going to throw out the idea that the short trip vehicle is on the path of some catastrophic event as being a holder over from days past,we feel very comfortable passing on this type of info because of a study that XYZ oil company did in 1965 I want to see some new data.

We are today blessed with better oil additive packages,better engine controls (both in engine performance and warm up) we no longer run our cars with manual chokes closed for long periods messing with our oil. Engine materials, tolerences,quality control,design improvements all have changed how long our cars engines last and the influence that our operating parameters have on that lifespan.

Some design errors slip through like BMW’s nikaseal engine blocks and Toyotas oil sludging problems. I am not stuck on what my father or gradfather had to do to just get 20K out of a set of rings.

And I know someone who smokes 3 packs of cigarettes a day, everyday for the last 71 years, is 92 and cancer free. That doesn’t make smoking any better for you.

Well, it is known that blow-by of combustion gasses leads to buildup of water, unburned gas, soot, and acids (sulfur and nitrogen oxides) in the oil. Getting the engine thoroughly warmed up fairly often will help get most of this stuff out of the oil, leading to less engine wear. The same principle holds for water-based crud in the exhaust system and rust-out. Maybe the effects aren’t nearly quite as bad as they used to be, but they’re still there.

“Resting” a car between bouts of short driving will do more harm than good, as the crud in the oil and exhaust system never gets removed. As suggested before, Mom should dump one of the cars and make sure the one remaining car gets a reasonably long drive each week.