I disconnected the battery of one of my two cars in March in anticipation that I would be driving a lot less. I have also put a car-cover over it. Looks like I will need the car only in September. Is there anything I need to do when I resume driving it? It would have been idle for six months.
Disconnecting the battery was a good idea. But the battery could still have drained a little due to a self-discharge phenomenon that occurs with lead-acid batteries. Hence you may need to jump-start the car.
Of course, you will have to re-install your preset radio stations and, in some cars, you might also have to re-programme personalised memory functions linked to each key.
During this time, check to see that all the instruments are functioning. Check the headlights, brake lamps and indicators.
Once you have started up the engine, check that it is idling smoothly. Then have a quick look under the car to see if there are any damp or oily patches. These may indicate a leak. Just to be sure, check your engine oil and coolant levels.
Do not rev the engine. Let the oil warm up and circulate to all of the various internal moving parts. In six months, some parts may no longer be lubricated as oil would have drained down to the sump.
Good synthetic oils can resist gravity better, but nonetheless, be gentle with the engine and let it idle for a few minutes before driving.
You might experience a stubborn parking brake that is reluctant to release. This happens because the pads or shoes have been exerting force on the discs or drums respectively and there is a tendency for surface adhesion to develop. Usually, the brake will break free within a few metres of driving. Only in very rare situations will the parking brake refuse to release. If this happens, you will have no choice but to have the car towed to a workshop.
The same can happen between clutch plates and the flywheel in a manual car. You will find it difficult to engage first gear. And when you do manage to shift to first, the car might creep forward even if your clutch pedal is fully depressed. Often, this will resolve by itself after a couple of kilometres.
Finally, if your car has been left covered all the while, it would be good to keep your doors and boot open for a while to allow some fresh air to flow through the interior.