2001 Saturn radiator

Actually, the cap on the "overflow" bottle is the way to check fluid level on your system. You would make sure the car is cold, remove the expansion tank cap and check the level. While you are there, it would be a wise idea to check for sludge etc. Inside the tank - this may indicate something going on elsewhere - and check hoses as well.

I suggest if you plan to do some of your own maintenance, investing in a Chilton's manual - or other reputable source, would be a great idea. Good luck.