PERMA-PRESS COOL DOWN ON WASHERS
If you followed the directions for washing PP fabrics they always suggested using a cold rinse setting. But on most KMs and WPs that had separate temperature settings in the 1960s and into the 1970s if you used the PP cycle and set the temp switch for a warm rinse not only would it rinse in warm but the CD would be all warm water. Huge waste of hot water, later machines would override the warm selection if used on the PP cycle.
Mark its too bad that your Grand mother didn't know that all she had to do to get a cold rinse on the normal cycle on the 1964 LKM was push the cold wash F button immediately after selecting a hot or medium wash on the normal cycle and the machine would give the hot or medium wash temp with a cold rinse. I think the owners manual explained how to do this, saving hot water is nothing new.