Well, that's a good question. I've never had either PS or Howes let me down. Never once. But, there was a tank full once when I didn't add either, and the temps seriously nose dived and I found myself limping into a truck stop to get some PS 9-1-1 to open my waxed injectors and it did the trick. And therein lies my question. The PS 9-1-1 didn't hurt anything, so I have to wonder with extreme cold, can you mix it in with your fuel that has already been treated with either PS or Howes as harmless insurance. Anyone know?
By the way, I use PS or Howes all year long, every tankful, trucks and tractors ever since the gel up, and I've not had a problem since. But...anyone know in the cases of extreme cold, if you aren't running No. 1 diesel, can you add PS 9-1-1 to make up the difference? Anyone know?