Vehicle & Equipment · Driver Training VideoFueling, DEF & Anti-Gel

Start with DEF — diesel exhaust fluid. Nearly every heavy truck built since 2010 runs a selective catalytic reduction system, and DEF is what makes it work. It's not optional and it's not a suggestion — federal emissions rules require the system to protect itself.

DEF has its own rules

Never top it off from a diesel fuel container, and never let diesel get into the DEF tank — cross-contamination can wreck the DEF injector and the whole SCR system, and that's a repair bill measured in thousands, not hundreds. DEF also freezes around twelve degrees Fahrenheit.

Now, the fuel itself

Diesel contains paraffin wax, and in cold weather that wax can start to crystallize — that's called gelling. Once wax clogs your fuel filter, the engine loses fuel supply and can stall, sometimes on the highway, sometimes on a grade, always at the worst time.

Your company standard: run a winter-blend or anti-gel additive anytime the forecast calls for temperatures near freezing or below, keep your fuel tank at least a quarter full at all times, and check your DEF level during every pre-trip — don't wait for the dash warning.

If you do start losing power in cold weather — surging, stalling, or a rough idle — get off the road and call it in before you're stuck fighting a gelled fuel line on the shoulder in the dark. A ten-minute call beats a four-hour tow.