radiator cap won’t open
First–Is the engine stone-cold?
I hope so!
Are you pressing down firmly on the cap while turning it counter-clockwise?
Did you push down on the cap before trying to open it?
The above advice is important. In my experience, you can turn the cap counterclockwise for part of the way, then you run into resistance. At that point, press firmly down and continue to turn it until it is loose.
Yes and big pipe wrench if it is stuck.
Take it to your shop, shouldn’t take much time. They solve this sort of problem on a daily basis. If you decide on a diy attempt, be very careful with how much force you apply. Possibility of damaging the radiator, requiring replacement. If diy’ering, only when cooling system is cold. You also might try heating the cap with a hair dryer a little to increase its dimensions. I have to say, I’ve never had this problem in over 60 years of driving. Radiator cap problems are usually they leak or won’t stay on.
If you can’t get the cap off, take it to a shop, and they’ll use a radiator cap wrench to loosen it for you.
If this is the original cap, after you figure out how to remove the old one, and time to put it on again, suggest to use a new cap.