Continued overheating, coolant spewing from radiator when warming up...

[Da6onesupra]

Having a problem with overheating. 87' 7-MGE started overheating when the weather was cold 2 weeks ago, but then would cool down after driving it on the highway. Last week it started getting hot while driving on the highway and cooled down after I had to pull off to the shoulder and turn the car off. I brought it home and left it in the garage. I put coolant in it the next day and it ran perfectly.

Started it the next day and while idling and warming up the radiator light came on in the dash. The car was still relatively cold (temp gauge at about 10-20%) and I opened the radiator cap; coolant spewed out everywhere. The radiator light then turned off on the dash, however after warming up the engine then began overheating again!!!

I thought it was the thermostat, so I replaced the thermostat and it is still having the same issue!!!! Please if anyone has an idea of what it could be, respond and give me some pointers...thanks