When storing a car for any extended amount of time I always try to do the following things:
1. Change the engine oil. Oil that has been run for some time accumulates the by-products of combustion which tend to be very corrosive to internal engine parts especially the bearings. One of the most common observations I have made upon opening an engine that has sat for some time with old oil is that the main and rod bearings have blotches on them where the oil has attacked the bearings. When changing the oil remove the cam cover and suck out most of the oil in the cam galleys (this process is not needed when doing regular oil changes) and change the oil filter. Start the car and run it just long enough to circulate the oil (maybe a couple of minutes). This will significantly reduce the risk to the engine from old oil.
[Regarding an oil change: 1) Try to drain the old oil from a warm engine, since more impurities are suspended in hot oil than cold oil. 2) Before installing the new filter, fill it about half way with fresh oil. This decreases the time it takes to reach normal operating oil pressure when the car is started. RHH]
2. Flush the cooling system and refill with distilled water and antifreeze. I install a flushing tee made by Prestone into the heater hose which allows you to hook up a hose to the tee and add water to the system while it overflows from the open radiator top. Turn on the heater and run the car until the water runs clear. Then drain the radiator from the drain plug and if you have an older car drain the block from the exhaust side petcock. Refill the system with at least a gallon of antifreeze or possibly a higher ratio if needed for low temperatures. (We don't know about those things in California). This process will assure that the pH of the cooling system is such that no attack will be made on the internals of the radiator or block caused by acidic cooling fluid.
3. If it has not been done for a while it is also a good idea to flush the brake system. Brake fluid is hygroscopic (it readily absorbs water, try adding water to a cup of brake fluid and see what happens). When the brake system sits for extended periods of time the water in the brake fluid will begin to attack the steel and aluminum brake components. To do this job use a turkey baster to remove the fluid from the reservoir and refill with new fluid. Bleed the brakes by attaching a plastic hose to the wheel cylinder bleed screw. Open the bleed screw and have someone push down on the brake pedal - close the bleed screw and then have your helper release the pedal. Continue to do this until the fluid runs clear. Don't forget to keep the reservoir full so that no air will enter the system. Start with the right rear then left rear then right front and finally left front. Don't forget to do the hydraulic clutch on newer cars.
4. Fill the gas tank. Rust will occur when a tank is only partially filled and it comes in contact with the air. If you suspect that there may be water in the tank you might want to consider draining the tank before refilling with clean fuel or run a tank of gas through the car after adding a product designed to remove the water.
5. Raising the car so that the tires don't sit on the ground is also a good idea. Put jack stands under the rear axle on a Spider. In the front, I tend to support the car with stands under the frame rails, rather than under the jacking points. I’m a little nervous about having a stand under something that moves in an arc. And since suspension pieces move, putting jack stands under the spring pans seems like a bad idea.
6. Remove the battery and store it where it won’t freeze. Wash it with a solution of baking soda (one Tablespoon) in a quart of warm water and then dry it. If you have a trickle charger, hook it up and turn it on for 24 hours at least once a month.
7. The nice part about doing all this before storing the car (aside from the protection it will give) is that the car will be ready to go when spring comes around.