Cooling System Issues with thermostat

[91 Sport 90K 94 XLT 157K]

My thermostat is sticking open and i cant even get warm air through my heater no matter how long i drive or how long i let it warm up. I recently just bought a new thermostat and a new seal. but the t-stat has no weep hole at the top like other ones have, is that going to be a problem? id imagine that it would fine but you never know, and i also read somewhere on here that if you drove around with a stuck open theromstat that it would cause your engine to go in loop mode causing poor mpg and cruddy engine performance? but im not having any of that. I dont suppose it would cause any damage would it? its cold up here in North Dakota and ive been able to put up with it before it started getting in the 10 degree weather. and also, before i change it how much fluid would i need to drain? any preperation steps would be greatly apprieciated. after all that is done, is it criticle to get all of the air out and burp the cooling system?, what is the best way to make sure and tell if you dont have air in the system? sorry if im asking to much, but as always any information will be kindly appreciated

 

[Corik]

when I changed mine, I let a gallon drain out. I don't think that much was really necessary. just make sure the hole is at the 12' oclock position. I know your supposed to burp the system, but when I did mine I just sealed everything up and ran with it. I haven't noticed anything bad. I heard that it will give bad temp readings? idk it runs fine, only bad thing is I cant get it to seal good. I think the guys who put the last one in tightened it wayy too much