1993 ford crown victoria lx new battery, car stopped, won't turn on???

I own a 1993 Ford Crown Victoria that, generally, runs great! However, last month, steam started coming from the engine into the car...so, I had an amatuer mechanic look at it and he said that the hoses were good but that a treatment should be put into the place where the antifreeze goes. I paid the man for his trouble, he put in the treatment and never came back. I checked on the bottle and discovered that the treatment should have been drained 3 days later. It is now over 1 month later. Most of the steam problem stopped, however, this last week the car started stopping while I was driving in the lower speeds (under 15 miles per hour--usually, parking lot speed). It completely stopped and I just coasted to a safe place. This happened, maybe, 5 times with the first 4 times my waiting for the car to cool down and then restarting it working just fine to get the car to start again. However, this last time, the car stopped as I was driving into my driveway and wouldn't turn on again. Note: the engine guage on the car was bouncin all over the place--from 1/2 full to empty ,so I put 4 bottles of 40point oll into the car and it was just barely enough (this was before the last two times that the car stopped. Please advise.