i have a 2002 buick that is over heatingso i flushed radiator changed thermostat so it work for 24 hours but i keep getting air in my coolant system its been pressure tested no sign of blown gaskets

Just run it with the Cap loose So it will burp all the air out of your coolant system

i have tried it seems to suck the air right back in

Then you have to add coolant

The proper test is a combustion leak test. the kit is about 40 bucks. Also, many mechanics have a sniffer for your exhaust that will tell the tale

the combustion test kit is that something i can get a autozone

they should have it, i know napa does. you will need some kind of vac pump to suck air through the blue fluid. some kits come with something for that. you will see what i mean when you look at the kit. Scottykilmer.com has a great vid on how to perform this test check it out.