Think You Know it All?

I just bougt a 1987 420SEL. The car has 99,000 miles on it and is in pretty good shape. I drove the car for about a week with no problems untill yesterday. The second day I had the car on the road I added some injector cleaner to a full tank of gas.
A day or two later I drove down to the beach, about an hour and a half away. I came back the same night and the car was great exept the coolant level light came on and off a few times. I checked the levels and everything looked OK.
The next day, after my 1/2 hour commute home I stoppped for some gas. About 2 blocks from the gas station I noticed some white smoke around the car. I got a little nervouse and drained a little coolant and added some fresh antifreez and water. I smoked all the way home.
The next day.......I checked the coolant. With all the levels checking out OK I drove to work. The car wasn't smoking? I got all the way to work with no problems! On the ride home after getting off the highway I stopped in a lot and it was smoking just a bit. Within 10 min after noticing the small amount of smoke it had turned into a huge amount of smoke? ALL the fluid levels are fine, the car has plenty of pickup and the smoke doesn't smell? WHAT IS GOING ON????????!!!!!!!!