Chevy Cavalier Overheating

Ok. I purchased a Cavalier from a friend, it wasn't overheating on him. It sat for about 2 years before I got it on the road.
I didn't notice anything wrong with it at first, I did a oil change and transmission fluid change on it, and it had a rough start were it almost died but come back.

I also had a few moments were when it was warmed up it didn't want to start, I noticed I could tap the gas pedal and it starts. Just warm not overly hot, but its intermittent.

Anyways the coolant was almost at its 150,000km's mark (131,000km's) and I thought its old, probably older than the 5years so I took it for a flush and fill.

First of all they did it off a hose that I didn't think they should have, almost guaranteeing air to get into the system. I was told to drive it home and open the resevoir cap... reluctantly expecting to be sprayed I did and actually all that happened was pressure release. So I closed it up and then on a drive I pulled into home and realized the temp gauge maxed out.
Thinking ill let air out I let it drop in temp abit and opened it and coolant started to come back at me like I expected to happen the first time.

So I had to top the system back up when it was cold, and I did. All was fine until today it started creeping back up. I kept it cool till I got home by getting up to 70km/h then going to neutral and coasting and could watch the temp lower.

Is this caused by air in my system... I spent several hours with the reservoir cap off and the car on... I wish the cavalier had a rad cap like normal cars...

how does the bleed valve that's installed work? am I supposed to warm up the car then open the valve? should I open the valve with the reservoir cap off? I cant open the reservoir probably without spraying coolant out again...