The car sat maybe 2 weeks, while I was in florida, and when I got back I took out my 4.10s and put back my 3.08s because of some noise and a chipped pinion. Well the car ran ok and what not but on my way home from school a day later my car temp climbed to the O and and mid N when I made it to my house which was a block away from when it started, So I figured I had air in the system so i went to auto zone for some parts unrelated and I ask if the had a 160 t stat, no they didnt for a mark but yes to a mustang GT 170 t stat. So I bought it and it climbed up again, so the next day I deciced to bleed the are out better so I let the car run for 30 minutes with the cap and crossover open, the car temp never really got to M but the t stat never opened, so I closed everything up drove to work it was fine, drove after work fine and to and from school today ran at the A all day and its 80 out side to so what gives, why is the cooling system such a pain

how do you bleed the system exactly?

I thought the cap had to stay in place, and only the crossover be opened up...?

crossover is what, the cap on the overflow reservoir?

Same problem i had back in december.

The cap is on the crossover tube....and yes...you leave it open and run the car. when its starting to lvl off, you add more through the tube.

Just a thought, when I changed my radiator out, I had the car pointed up the driveway. Air is going to seek the highest point, the crossover, and the engine was pointed upwards, giving the air a better chance to be forced out.
I hadn't had any issues with air pockets. I might have been lucky on this one.

the mustang gt t stat works right, cause on another site they said it wouldnt but, my car has been running nice and cool on these 80 degree days

Same thing happend to my 93 the other day. Temp went up and then came back down. No problem since.

ya it seems to happen if my car has been sitting awhile last time my trans went out the car started running hot then my rearend the car ran hot so I think air builds up and causes this