New to this forum

Well i am new to this thing, but i would like to ask u all a few questions regarding my lumina. first of all i own a 1990 chevy lumina 3.1 v6 euro she has 238,000kms but im having a few problem and i was hoping maybe some of u could help me! well ive been having problems with my temputre gage, since it started to get warmer out it runs preetty high and the other day when i was driving it went to the red line and the light started flashing, i went to pull over to make sure the coolant was all good but all of a sudden it went back down to normal. Any suggestions? Next is my power steering, when the car is cold the steering makes a really loud noise untill it warms up. i add fluid on a regular basis, but when i drove to the gas station the other day and decided i was going to check my fluid , i opened the cap up and all the power sterring fluid was foamy, anyone know what it could be? Any help would be greatly appreciated!

Basics first, is your cap allowing the correct pressure in the system? How's the airflow through the A/C condenser (the thin radiator looking thing in front of the cars radiator) thence through to the radiator itself. How's the health of the coolant?
The sudden temp swing can be associated with a faulty thermostat. After the basics, that's the first thing I'd check.
Good luck.