94 buick lesabre

I am having trouble with my car. he service engine soon light comes on and a red light flashes above the temperature gage. Before this happened my car would just die as I was driving down the road. It hasn't died lately, but I took it to the dealer and they said the temperature sensor chip was out and replaced that, then they found electric current in the radiator and said old anti-freeze could cause this, so they drained the radiator and put new anti-freeze in it and the light went off. They said I needed to do an engine flush, but I had to wait til I had more money. Well, I drove the car for a couple of hours and the ses came on and the little red light started flashing. Any ideas? Is it safe to drive like this? thanks