Diesel Exhaust Fluid (DEF) Guide: Storage, Freezing and Buying in Bulk

If you run diesel trucks built in the last decade, Diesel Exhaust Fluid (DEF) is as routine as fuel. Run out and most trucks go into reduced power mode. Store it badly and you can damage an expensive SCR system. Here is what every fleet manager, shop and gas station should know.

What is DEF?

DEF is a mix of about 32.5% high-purity urea and 67.5% deionized water. It is sprayed into the exhaust of trucks with a Selective Catalytic Reduction (SCR) system, where it breaks down harmful nitrogen oxides (NOx) into nitrogen and water. It never goes in the fuel tank — only the separate DEF tank, usually marked with a blue cap.

Always buy DEF that meets the ISO 22241 standard and is API certified. Contaminated or off-spec DEF can clog injectors and damage the SCR catalyst.

Does DEF freeze?

Yes. DEF freezes at around 12°F (-11°C). That sounds alarming, but it is normal:

• Trucks with SCR systems have heated DEF tanks and lines that thaw the fluid after startup.
• Freezing and thawing does not harm DEF quality.
• Never add antifreeze, alcohol or any additive to DEF to stop it freezing — this will damage the system.
• DEF expands about 7% when frozen, so do not overfill tanks or sealed containers.

How to store DEF

DEF has a limited shelf life, and heat shortens it. Follow these rules for your shop or yard:

• Store indoors, out of direct sunlight, ideally between 12°F and 86°F.
• Keep containers sealed until use to avoid contamination.
• Use dedicated, clean funnels and pumps — never ones used for oil or coolant.
• Rotate stock: first in, first out.
• Check the date code on jugs and totes.

Buying DEF in bulk

Fleets and stations can save a lot by buying DEF by the case, drum or tote instead of single jugs at the pump. Bulk buying also means you never get caught short on the road.

RPS Distributors carries leading DEF brands including Blue Sky, Peak, Colonial and BlueDEF in 2.5-gallon jugs and larger sizes. Browse our Diesel Exhaust Fluid (DEF) collection.

Keep your trucks moving

Whether you run five trucks or fifty, we deliver DEF and diesel supplies across New Jersey at wholesale pricing. Request a wholesale quote or call 1-855-498-7509.