I think that washer fluid makes your car run a little cooler. Isn't that coolant addative some kind of alcohol? If it is washer fluid wouldn't do much. Don't feel bad I almost got fired one time for leaving a radiator cap on the first click not the second. When the car got hot coolant gushed out of the radiator when the lady was going home. And she noticed the car smoking and proceeded to drive for another 20 miles that way. She had her vehicle towed back in from her house. It was ok just a little low on coolant. My boss got really hot he was telling me to change t-stat, gasket, head gaskets, basically anything to make this woman happy. I told him that it wasn't my fault she was an idiot. When your car smokes and you just had it worked on you should pull over and raise hell not drive another 20 miles. But in the end I filled it back up with coolant, road tested it for about 20 miles to see if it ran hot. It turned out ok. I just had to swallow my pride and admit I made a mistake. More then half of the techs I worked with at the dealer didn't even do fluid checks and I always did. So I guess my concern for customers caught me in the end.