I have a 87 jeep cherokee well it just turned cold here and my heater would not get warm at all hardly so I pulled the thermostat housing to check out the thermostat well it didn't even have a thermostat so I bought one and put it in tonight and have not cranked it yet to see if that fixed the heater the people I bought the jeep from took the thermostat out so I'm guessing it was running hot wats you guys input on this and if you think it is running hot let me know what you think is causing this

 

I think your going to need to start it up, and see if it is still running hot. Thats the only way to know. Don't try and figure out why previous owners do things. You never will!
Make sure to get all the air out of the system when you do.

 

I'll bet after the water pump, radiator and fan clutch are replaced, the heater will work fine and it won't overheat.