Hey guys, I was super worried because I might of melted my cap onto the tank, but in the end I got it open and here's how...
If it's just too tight.
Then, seriously, just heat the car up, by either idling/revving OR driving it until hot.
hen turn the car off and wait for 20 minutes (not enough for the car to fully cool down).
Go ahead and wear a glove and covering your face (nothing happened to me, but safety first), slowly open the coolant cap (remember lefty loosey). Loosen the cap only about a quarter of a turn, and never fully or even till pressure escapes. Then you should leave it, wait till it cools down fully, then it'll be safe enough to fully open the reservoir cap.
I got mine open after work, when I got home, went upstairs cooked something to eat, came back down, and did as described above. Haven't checked on it yet. Will do in the morning when I go to work again, I'll just add some anti-freeze. It's ratio is consistent of mainly water at the moment. After my car overheated on the way to work a week ago, because I didn't put the cap back on properly the pressure boiled over, spilling antifreeze all over the engine.
If that doesn't work. Buy a wrench that fits around the cap and wrench it open that way, but try to do this slowly so you can assess the situation and not cause further damage. UNLESS of course it tells you specifically to push down before twisting.