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 . . .

 

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 ...