i need comforting awnsers

well i got her fired up today but im worried, she busted right off, has 45psi oil at idle and is smooth, buttt i let it idle for quit a while wating for the termistat to open it never did my temp sensor is in the upper hose so i dont know how hot it got but the engine changed sound so i killed it. it fires right up but im concerned i think ill put a new stat in it for safety but i wondering if i alread hurt the motor since the idle changed and it sounded like it was struggling a bit, of chorse i may be overworked caus it has been sitting 3 years it could have been, an injector, or anything my mechanic friend said it could take as long a 15 min for it to open it ran a good 15 min with no circulation, i dont even know how much coolant is in the block i put 3/4 gal antifreese and 3/4 gal water in the expansion tank i left the lid off to add more as it went down but it never did

Probably air in the system.

disconnect the air bleed hose on the front of the cylinder head and leave it off until you get a steady flow of coolant out of it with the engine off. Park it on a hill with the front of the truck higher or jack it up so that the air bubble moves to the front of the engine.

i was looking at this a few min ago it appears that the thermostat is in the suction line does that mean when i filled the expansion tank up the coolant all went into the radiator and i ran the engine dry. im relly hopeing i did not gall the pistons or some crap. i did not relly pay much attention to that i just assumed that by filling the bottle where the cap is i was also filling the block. you know you can get in a hurry after you wait 10 years. I know the computer monoters the temp but i don't know what it does to compensate for a over heating engine. It did not sound bad just the rpms changed and acted like it was fixing to die. I killed it it fired back up and idled fine. my luck though i warped a head or something and wont find out till i get coolant in it. I figured ill let it cool over night then acces the issue cold water and hot metal don't mix lol