I've seen windshield washer fluid used in place of a product called 'Heat" in diesel engines. Before I retired, the people who used to service our emergency generators kept gallons of washer fluid on the trucks to add to the fuel tanks in winter. Got my attention when I first saw it but they swore by it and we had a full service contract so if the engines messed up, they were responsible for them.
STP: LOL, I once worked for a Chevy dealership. They used to add STP to noisy differentials in the used cars. Made them quieter, that's for sure. At least until they were out the door. And, an old mechanic once told me that 'back-in-the-day' they used to mush up bananas and fill a noisy differential. He swore it kept them quiet. Now that I think about it, doesn't WD-40 sort of smell like over ripe bananas?
Wow, talk about highjacking a thread..................