Many of us have a second car that isn't used much; maybe we keep it under a car cover in the garage or -- worse -- just let it sit there in the driveway. This is not wise -- unless your goal is to end up with a 3,000 pound pile of West Virginia lawn sculpture.
In fact, a car with higher miles that's used every day can be in better shape -- and even last longer, ultimately -- than a car that's basically left to rot. And that is exactly what happens to a vehicle that is not properly stored or properly kept-up if it's used only occasionally (less than a couple of times per month).
For example, rubber seals and gaskets in the engine will dry out, crack and eventually leak if the engine is not fired-up and run until it reaches operating temperature. Engine oil keeps them pliable. But it has to circulate to reach many of these gaskets and seals. And for it to ciruclate, the engine has to be running.
Clean, fresh engine oil is also vital to the health of internal engine parts. Normally, the oil is supplied under pressure (or by splash effect) when the engine is running -- and afterwards a thin coat will remain on these surfaces, protecting them.
However, the film of oil that protects those internal metal surfaces will eventually dissipate -- or worse, congeal into a blob of sludge. Sludge can cause sticking valves, oiling system problems and other engine maladies -- while rust can form on the insides of cylinder walls from the mositure that gets into the engine during long periods of disuse, when there is an absence of lubrication.
Old gas inside carburetors and fuel systems leaves varnish and deposits; the gas also leaks into the engine and will wash the protective film of motor oil off of internal parts and contaminate the oil in the sump (oil pan).
Grit and gunk can cause accelerated wear, even catastrophic engine failure, when you try and start the thing after months sitting idle. At minimum, it will likely cause hard starting/rough running and poor overall performance.
Corrosion can also build up in the passages of the cooling system -- with crud building-up in the engine's cooling passages, radiator, and the heater core. This will reduce the efficiency of the cooling system and could lead to overheating -- and expensive repairs.
Some automatic transmissions can be ruined (or their lives shortened) by infrequent use; the hydraulic fluid that makes them work is also a lubricant that keeps parts such as the front pump in good working order. If seals dry out or internal passages get blocked by crud accumulated from disuse, a failure can occur when the car is eventually restarted; hydraulic problems/lack of proper oil circulation can ruin an automatic transmission very quickly.
Moisture will eventually ruin brake parts. The fluid gets contaminated and the rubber lines begin to dry rot -- or rot from the inside out. Rubber seals at calipers and wheel cylinders wear out and rust can form on disc brake rotors.
To avoid all this, you must do one of two things -- either prepare the car properly for long-term storage -- or operate the car for about half an hour or so at least twice a month.
"Operate" meaning actually drive it -- not just running the engine at idle while the car sits just there. If you don't actually drive the car, gear oil doesn't circulate in the axle and transmission (manual-equipped cars), the brake rotors and drums don't turn and the engine -- when it isn't running at more than idle speed -- isn't getting the same workout it would if you actually drove the thing.
Some people don't realize it, but simply starting the car and letting it idle is one of the absolute worst things you can do. It's especially hard on late-model, emissions-controlled vehicle because the catalytic converter and related components do not work properly until normal operating temperature has been reached. To maximize the life of these parts (as well as keep your contribution of noxious gasses to the environment at a minimum) drive the car almost immediately after you start it.
A 30-45 minute toodle will recharge the battery, circulate oil to internal seals, allow the engine to purge itself of volatile and corrosive compounds, keep the cooling system in peak shape (assuming you've kept up with maintenance of that by regularly flushing it and adding fresh anti-freeze and water), and keep the transmission/axle or transaxle (on front-drive cars) lubed.
Do this faithfully -- and adhere to a proper maintenance shedule -- and the car will last a long, long time. Fail to do it and you will have a very heavy but largely useless object d' art in your driveway.
As regards long-term storage, there are many books available on the subject (see the "transportation" area of your local book store), and it would take a separate article to detail the process. But it's definitely worth looking into if you have a car you don't plan to use for more than a couple of months at a stretch. At least, that is, if you value the car in question. For a vehicle that won't be used for six months or longer, proper storage is an absolute necessity.
Most people, however, will get by just fine with the above "twice a month" rule.
