well, can you describe what the windshield resevoir is hooked up to and what is the coolant expansion tank hooked up to and what do the caps for each of these look like? That would be a really good place to start. Take a look, are the caps metal and do they screw off or are they plastic and flip open. Second, under what circumstances does this happen? Does the car overheat when this happens? What color is the liquid boiling over, and lastly has the car been out of your hands for service lately.
1985 190e 2.3