H18WK04 Fuel filter

Compact spin-on fuel filter for MAN diesel engines, equivalent to MAN OEM 51125030045. Typically fitted to medium-duty TGL and TGM platform variants, the H18WK04 provides primary fuel filtration and water separation in a low-profile, easy-access format suited to tighter engine bays. Despite the smaller size, the protection it provides is identical in function: removing particulate and free water from diesel before it enters the injection circuit. A fuel filter left beyond its service interval restricts flow progressively — the first sign is hesitation under acceleration and reduced power at high load, advancing to hard starting and eventually complete fuel starvation as the element becomes fully blocked. Hengst manufactures the filter in Germany. When fitting, the most common installation error is failing to remove the old O-ring from the filter head seating face — the retained O-ring combined with the new filter's seal creates a double-seal condition that leaks immediately under fuel pressure. Pre-fill the filter body with clean diesel before installation and check for leaks after the first start before returning the vehicle to service.