Why it matters
Water and dirt damage injection pumps and injectors. Common-rail engines and the 24-valve VP44 are especially sensitive, so filter makers and Cummins both stress filtration and water separation.
What owners do
- Drain the water separator when the water-in-fuel light comes on, and at the interval in your manual.
- Replace filters on schedule with filters that meet the engine maker's specification.
- Buy fuel from busy stations with fresh turnover.
- In winter, use fuel suited to the temperature. Gelled fuel plugs filters first.
After a filter change, prime the system the way your manual describes.
Where this comes from
- Vaden: Fuel filter / water separator guide for heavy-duty diesels (PDF)
- Auto Care Association TSB 91-1: Solving winter diesel fuel and fuel filter problems
- Coordinating Research Council report CRC-671 (diesel low-temperature operability)
- Cummins: Motorhome quick reference guide, B6.7 / ISB (PDF)
- Blue Chip Diesel: VP44 and lift pump information (PDF)
Last reviewed 2026-10-19. General information only: your owner's manual and service information come first.