Why is my 1987 Jeep Cherokee overheating?

I have a 1987 jeep cherokee! The engine is a 6 cylinder 4.0 l i think!I can't keep it from over heating. I have replaced the thermostat with the same one that read 195 Fahrenheit. I let it sit idling for about 15 20 minutes. It started bubbling at the overflow bottle. This Jeep does NOT have a radiator cap on the radiator. The clutch fan seems to be working. I tried to stop it with a bottle. The water pump is not dripping water. I can feel the water flowing threw the top radiator hose. Though it doesn't seem like it was flowing that fast and it seemed as if it got hot real quick. Should the water flow slow or fast threw the hoses? I checked the temperature gauge it was reading about 195 to 200. But why would the overflow bottle start to flow up and bubble. I didn't have the screw cap on the overflow bottle. I lost it somewhere in between the engine and the fender well. Could the cap not being screwed on the bottle cause the overheating? Not creating pressure? I noticed a little water in my passenger floor under the dash. If the heater core is clogged could that be a cause? Im all out of idea's

DETAILS ABOUT THE CAR: IT has been sitting for 2 YRS. then started and drove for a few weeks then sat for another YEAR & HALF. ITs been overheating senice i cranked about two or three weeks ago??
THANKS FOR TAKING THE TIME TO READ AND ANSWER MY QUESTION!!!!!!