Cursa Fuel Co. / Learn / DEF Basics
DEF Basics
Two to three gallons of DEF per hundred gallons of diesel. Small enough to forget, which is exactly why it strands trucks.
Plan on two to three gallons of DEF for every hundred gallons of diesel your fleet burns. That two-to-three-percent ratio is the working number for most modern diesel fleets. It sounds small, which is exactly why DEF sneaks up on operations that only track diesel.
DEF runs at roughly 2–3% of diesel volume, small enough to forget until the derate warning hits.
Because DEF burns so slowly relative to diesel, a fleet can go weeks without thinking about it, then hit a low-DEF warning, then a derate, mid-route. The truck does not simply slow down. It drops to a crawl and forces a shop reset. A fuel you barely notice becomes the reason a truck is on a hook.
The fix is to stop tracking DEF separately. We deliver DEF on the same run as your diesel, sized to your actual burn, so the ratio takes care of itself and the warning light stays off.
Fuel delivery and emergency fueling across Upstate South Carolina and the Southeast. Scheduled service, emergency response, and everything in between.