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Originally Posted by Bladecutter
It should always be changed right before being stored, so it would be done in the winter. There's no need to change it again in the spring, simply from the fact that the new oil poured in has 100% of its acid neutralizing properties, and since there isn't any combustion events occurring when the engine isn't running, the oil isn't having any new acids being produced to cope with.
Basically, the last drive in the winter should look like this:
Take car to shop and have oil change performed.
Drive car home.
Put car in garage.
Pop hood, and hook up the battery tender.
Turn out lights, and lock garage.
BC.
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With an internal battery, like the Boxster, I prefer to pull the battery from the car.
The Boxster uses a vent tube to vent away any accumulated Hydrogen or Oxygen gas. There can also be minute amounts of sulphuric acid in this vapor as well. Normally, the air rushing past the open end of the vent tube creates negative pressure (vacuum) pulling these gasses out of the tube and away to the atmosphere.
But, when the car is not running, no air is rushing past the vent tube and so no gasses are extracted and can buildup to the point, over a several month storage peiod, where they accumulate under the hood. The Hydrogen and Oxygen pose a fire and explosion risk, but the sulphuric acid can condense on cold metal parts (hood, firewall, electronics, etc.) and can lead to corrosion - rust. Also, the battery maintains it health better in a warmer environment than in the cold car.
The downside, besides actually having to disconnect and carry the battery away, is that the DME, Tiptronic Control Module (if equipped) and Radio lose their memory functions (and security code in the case of the radio - pre-'03) and will have to re-learn once the car is put back into service. But, this is a minor inconvenience and these things re-learn after just a couple drive cycles.
