Cause for concern?
 

Went to my local Mobil station to get my windshield washer fluid filled and they put it in the engine coolant reservoir! Is this cause for alarm? Do I need to have engine coolant flushed? I drove the car 150 miles before realizing the error and everything seems to be fine . . . :confused:

Uh, I would get the system flushed. I don't know what the reaction will be, but I can't believe it helps the coolant.

Get it flushed. Document the situation in case there are problems (blown head gasket, overheating) in the future: date, time, reciept, what they did, when you discovered it, etc. It can't be good for it, although hopefully it was not bad for it. Might not have hurt the engine, but ...