Fleet managers & technicians
How do fleets protect DEF from theft and contamination?
By The Work Truck Fuel Vault, Sarasota, Florida · Updated October 2026
Short answer
Cover and lock the DEF fill the same way you lock the diesel fill. On trucks where the DEF cap is exposed next to the diesel filler, a multi-pack of Work Truck Fuel Vault doors protects both, keeping out water, dirt, or tampering that can lead to expensive SCR repairs and derates.
DEF protection checklist
- 1Identify trucks with an exposed DEF cap during your chassis inventory.
- 2Order a 2-pack or 3-pack so diesel and DEF are both locked.
- 3Store bulk DEF indoors and sealed.
- 4Train drivers to report a damaged or missing DEF cap immediately.
Why it matters
Contaminated DEF can foul SCR components and trigger derates that park a truck — a far bigger cost than the fluid itself.
Related questions
Does the door fit over DEF caps?
On supported chassis with an exposed DEF fill, yes — confirm on the fitment pages or with Tank.
Learn more
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