I've been using STPP in my laundry since I figured out around 2001 that it was the missing ingredient in the Kirkland Clout detergent I used to like so much. Once I saw the dramatic improvement in washing it gave, I was also hooked. I clued in the crowd over at That Home Site on Garden Web. Some still felt it was wrong to use it, despite the fact that the average family flushes more phosphorus down the toilet and garbage disposal than a typical washing machine using phosphated detergent.
Only one quibble with what has been said so far: STPP wouldn't last long in antifreeze. Instead I think what is added to that is TSP. And in Europe phosphate has been phased out of antifreeze there because it forms a precipitate in their very hard water that can clog radiators. Over here I generally use distilled water in my radiator, regardless of the antifreeze formulation (and there are a lot of varying antifreeze formulas on the market today, with color being no reliable indication of what it actually is). Interestingly, silicates are also added to most antifreezes, for the same reason as they are added to laundry detergents: to protect metal parts from corrosion.
