[Razorback1980]

The oil filler cap isn't the same as a radiator overflow cap. The radiator overflow cap has a spring that helps set the pressure inside the cooling system and that function isn't a part of the oil filler cap. The primary function of the oil filler cap is to keep things out of your oil and does not regulate oil pressure in any way. If the "O" ring is worn and not creating a seal between the cap and the filler tube, dirt may get into your oil which is something you don't want. If mine ever does that, I'll try replacing the o-ring first but as long as the oil cap tightens down meaning the threads are not stripped and creates an air tight seal with the filler tube, it should be okay. One check may be to start the engine and see if you can feel any flow of air from around the cap threads. If you can't feel air moving around the bottom of the oil cap, it should be okay. Hope this answers some questions.

Tom