Reference
Reading a Fleetguard filter number
The letters in front of a Fleetguard number tell you what the filter does. What LF, FF, FS, AF, WF and HF mean, and why coolant filters are the ones most often skipped.
The prefix is the filter type
Fleetguard numbers start with letters that say what the filter is, so you can tell a fuel filter from an oil filter without opening a catalogue.
LF is lube, meaning engine oil. FF is fuel. FS is a fuel and water separator. AF is air. WF is water, meaning coolant. HF is hydraulic.
So LF9009 is an oil filter and FS19652 is a fuel and water separator, read straight off the number. The digits that follow are the individual filter, not a size or a rating, so there is nothing further to decode from them.
Fuel filters and separators are not the same job
An FF filter removes particles from diesel. An FS separator removes water as well, by giving it somewhere to drop out and collect, usually in a clear bowl with a drain at the bottom.
Water in diesel does more damage than dirt on a modern injection system, and a separator only works if somebody drains the bowl. A separator left undrained until the water is carried through is doing no more than a plain fuel filter would.
The coolant filter is the one that gets skipped
A WF filter is not just filtering the coolant. Most of them dose the system with supplemental coolant additive, which is what protects cylinder liners from pitting and the system from corrosion.
On a wet sleeve engine that matters a great deal. Coolant that has lost its additive lets the liner walls pit under the vibration of combustion, and by the time that shows up the repair is an engine strip rather than a filter change. A set running on plain water has no protection at all.
When a service interval is being cut to save money, the coolant filter is usually the first item dropped and the most expensive one to have dropped.
Cross-referencing from another brand
Filters cross-reference cleanly between makers, more so than most parts. If what you have is a Baldwin, Donaldson, Mann or an OEM number rather than a Fleetguard one, that is enough to work from.
Send the number that is printed on the filter you are replacing, along with the engine model. Where a filter has been superseded, the replacement is often a different physical size, so it is worth confirming the housing it has to fit before ordering a quantity.
