Welcome back to our series on automotive tools for the beginning do it yourself mechanic. In this article I'm going to talk briefly about how to properly handle a difficult screw that just won't turn to back itself out. Screws tend to be more problematic than nuts and bolts in this manner simply because the head you are given to turn is much smaller and usually more fragile. If you live in an area where rust is a problem this is even more true. Typically the head of a screw will rust so badly that any miscalculation in how much force you should apply can ruin the screw.
The first thing you should try to do is turn the screw as if you were trying to tighten it, but just slightly. So give it just a little force clockwise. You don't want to use so much force that you strip the screw, hole or screw head - just enough to break the tension on the threads. Make sure that you apply adequate pressure downwards on the head, because if the screwdriver bit slips out of the head, you may destroy the head depending on how badly it's rusted.
Another helpful thing I like to do to break the tension on the threads is pretty simple. I'll put the screwdriver head into the screw, and tap the butt of the screwdriver down towards the screw. Don't hit it so hard that you might damage the screw or threads, just enough to break the tension on the threads. I normally use the handle of another screwdriver to tap with. If you use too much downward force you could potentially damage both the screw and whatever is below it, so be responsible with how much force you apply.
If both of those fail, I'd recommend lubricating the threads if you can reach them. If you can't reach the threads, spray around the outside of the head of the screw. Typically good penetrating oil will do the job. You will want to let it sit overnight if possible. However, under no conditions should you apply the oil if the engine or surface you are working on is hot. The oil can and possibly will catch on fire.