Piston Slap: A question of if and when?

Bill writes:

How often should cars be started when they are garaged and how long should they be run?

Sajeev answers:

This is a more difficult question to answer than one might initially consider. The answer depends on how long the vehicle will be stored. But before we proceed, read about the basics of car storage applicable to all types of storage durations/needs.

I’ve had cars sit for 1–2 years in a non-running, undriveable condition, while performing cosmetic restorations. When complete, I was surprised to see how well they ran on old gas when it was time to get ’em back on the road. They clearly ran better once I burned off the old gas and put fresh stuff in (and both were ethanol blends), but I’m getting ahead of myself: I’ve also had cars sit for 3 months and their fuel pumps died and/or carburetors got all mucked up.

There’s no easy answer, because life is more complicated than we intend, and we wind up neglecting the cars in our garages. So let’s lay out some scenarios for indoor car storage and try to answer them specifically.

1. Winter storage: Do the basics of car storage and don’t touch it until the weather is warm again and the salt is off the road. If you really want to hear it run (or if you don’t trust the fuel system) go ahead and run it in the garage until the oil gets to operating temperature. (Usually 15–20 minutes.)
2. Storage for less than a year: See #1, but add a fuel stabilizer (they make gas last for two years).
   2a. Storage for less than a year, alternatively: Start the vehicle every three months to see if the fuel system can handle running on “aged” gasoline. Run it to operating temperature or kill it immediately after realizing the fuel system is still in good shape. Do not run a stored vehicle if you don’t plan on running it for 15–20 minutes.
3. Storage for longer than a year: See #2 and consider the fact you might need to drain engine coolant, fuel, and oil out of the vehicle for a truly dry storage experience.

Keep in mind that these are rough guidelines based on my experiences with both EFI and carbureted vehicles; your mileage may vary. No matter which option you choose, remember one final nugget of wisdom: Driving is better for the vehicle than just idling in a garage.

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