Originally Posted by brian42

the gray bottle is the cetane boost and lubricity enhancer and the white bottle is the cetane boost only for winter blend. I live in So Cal and only use the gray bottle ("winter" is anything less than 60F out here).

I've been using it in mine shortly after getting my rig and I think it helps. Quieter and around 1 mpg better (after the first couple of tanks). Since mine is the 7.3 and my rubber o-rings weren't designed around ULSD, I use it to help mileage and to lubricate all those pesky o-rings.

I use the recommended amount. The bottle says you can't use too much and I'm sure I've built a stockpile of it from the residual left in the tank when I fill it. I buy mine at Wal-Mart for about $16 for a 96oz jug (16oz bottle is around $7). I have a small 16oz bottle that I just pour into and take with me to fill up. You can also get the 16oz bottles at Kragen's (Schuck's/Checker) and Pep Boys (Pep Boys also carries the 96oz jug too).