its loose
Neither your oil filter, or the fill cap need to be loose, the filter should be screwed on as tight as you can get it by hand only, and the fill cap should fit snugly so it does not come off. If the oil filter is loose or too tight you can blow out the seal which will cause you lose all your oil.
The threads are worn and the vibration of the engine causes the oil cap to loosen. Replace the oil cap or try a little teflon tape on the male thread as a temporary fix.
Yes, just had exactly the same problem, I tightened oil cap correctly and cleaned the oil thst has splattered around the engine compartment and it has solved the odour of oil / fumes.
Not likely but possible.
None, it might cause oil to spill on your engine or inside of your hood, or a dash light might come on.
That would be moisture in the oil.
Make sure the oil-filler cap is properly installed. Some engines rely on engine crankcase perssure in order to run properly. If the cap is loose or improperly installes, this pressure may drop or not allow for the proper venting of crankcase pressures. You may also have PCV valve issues as well. Start with the filler cap and go from there.
A major leak.
If its for your car it will leak oil faster and therefore make you change your oil more often.
Open the oil cap in the engine bay, jack the car up and on the oil pan theres a bolt, undo the bolt and the oil will drain, when its finished draining screw the bolt in make sure it is tight, put the car on the ground, change the oil filter, then pour the new oil into the oil cap hole, put the cap back on and your done. Make sure you don't put to much oil in, i think the recommended amount is 4-5l, check your cars manual to make sure.
I have never seen a locking oil cap. If you mean that it is loose or off, then you might get oil splatter all over your engine compartment. No big deal, as long as the oil level never got too low. Check the oil level, clean everything up and rest easy. No damage done.