My car coolant is bubbling until I stop and continues?

So, what are some ideas? Here's basically what happened:

Car: Toyota Tercel 1991 DX (Deluxe) with 135,000 miles automatic

So, originally my car stopped running after a short cold drive from my house to the store, and after coming back it stopped to where I had to push it off to the side of the road where we thusly called the Sheriff and explained the situation (It wasn't towed).

So, we got it home, my dad towed the car himself with his GMC truck and soon afterwords we couldn't get it started again, till we tried a silly suggestion my friend had: remove the gas cover and the screw (Don't laugh at me, I don't remember what it's called right now >_<)itself that you take off when you put in gasoline. Shortly after doing this, we tried starting the car again and miraculously it started, but to end this day of miracles (sarcastically) I drove my car around the neighborhood to double check everything was working, including heat. Heat was working as I pulled back into my driveway, we heard a bubbling noise inside the hood. So, I left my dad as he insisted to check what was wrong, and he came back to tell me, there was extra fluid inside the oil, which he didn't check what it was.

We haven't replaced the thermostat, but replaced the water pump, by a professional mechanic recently.

So...help?