Since I have been using the Motorcraft Cetane Booster @ 4oz per tank full(26 gallons) I have noticed the factory exhaust tips are turning a darker color. Before the Cetane they stayed pretty much grey. Been using same Exxon fuel station for every fill up as they run through alot of diesel.

I have read posts on here about issues and things that could be wrong if tail pipes going black, most say they should remain clean which mine used to. All filters are new and truck runs great.

I have noticed lately that it does a regen about every 300 miles and soot level goes back down and DPF shows 0% when done. I wasn't worried about the miles per regen as it varies 300-500 depending on how I am driving, mostly why is the exhaust tips going dark on inside.