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Don't remove a battery lead unless you know the radio code
If you are going to leave your car unused for a while there are a few simple things you can do to make sure that it will be in good condition and ready to use when you get back. What you will need to do depends on how long the vehicle will be left.
We've broken it down to 'up to a month', 'one to three months', and 'more than three months'.
If you're not sure if the battery will stay charged, a 'smart charger' is a great investment. These only charge the battery when it needs it and can be left connected without risk of overcharging.
In addition to the 'one month' points:
As an alternative to ventilation you could seal the garage and use a dehumidifier – cheaper and probably better than heating. (A dehumidifier will need a low-temperature shut-off though as it can't work below about 4C. Corrosion is not a problem in very cold weather, provided the car is dry and free from road salt.
In addition to the one month and three month points:
Petrol will stay fresh in a sealed container for about a year but starts to degrade in as little as a month when exposed to the atmosphere – the lighter more volatile fractions evaporate, lowering the fuel’s octane and making starting harder.
Petrol exposed to the atmosphere will start to oxidise over long periods too, producing gum and varnish deposits on fuel system components. This is more likely to be a problem with older carburettor fuel systems than with sealed fuel injection systems.
Stored diesel should be OK for up to a year, depending on temperature but will start to oxidise over longer periods, producing gum and other sediments that can quickly block filters when the engine is run again.
Bear in mind that diesel fuel specifications change through the year - fuel bought in summer will be much more susceptible to waxing in cold weather than winter diesel formulated to give protection down to at least -15C.
Unless you are able to ensure a dry stable environment, for periods over a month or so it is best to store a vehicle with a full tank of fuel to reduce the space for water to condense.
Condensation in the fuel tank can be a serious issue:
For long term storage, particularly of older (pre-injection) vehicles, consider using a fuel stabiliser additive. Stabilisers are widely used for garden machinery, and other petrol-powered equipment left unused for a couple of seasons as well as motorbikes taken off the road over winter. Follow the instructions carefully.
The work required to start a car that's not been used for a long time will depend to some extent on how well the car was prepared before being put into 'storage'.
Arrange a full service once the car is running again.
You can only drive a car without an MOT on the highway if it is being driven by prior arrangement to a garage for an MOT.
If garage work is required before the MOT then the car should be moved only by truck or trailer.
(24 December 2013)