Caterpillar 509-5694 Secondary Fuel Filter Element

The Second of Two Elements in the Fuel Line

On a 320 GC, 323 GC or 326 GC the fuel side of the service is not one filter, it is two, and they are different parts with different jobs. The separator element 523-4987 sits in the water separator housing upstream; its job is to take out free water and coarse contamination before the fuel reaches anything expensive. The secondary fuel filter element 509-5694 sits downstream and does the fine work. Cat's own product copy for the separator line says it plainly — Cat Fuel Water Separators are built to extend the life of your secondary filter and precision fuel system components. If the upstream element is doing its job, the downstream element lives longer.

Physically they cannot be mixed up on a bench. 523-4987 is 4.043 in (102.7 mm) across and 10.169 in (258.3 mm) long; 509-5694 is 3.484 in (88.5 mm) across and 6.654 in (169 mm) long. Both are cartridges with out-to-in flow and polyamide plastic construction, which is exactly why a photo of one looks like a photo of the other — and why the wrong element turns up in a kit marked with the right machine model.

Why This Number Gets Quoted Wrong

Two reasons, both visible on Cat's own pages. First, both numbers sit in the same branch of the catalogue — 509-5694 is filed under Engine Filters > Fuel Filters, and 523-4987 under Engine Filters > Fuel Water Separators — and both pages carry the same price-less "Check Price" and the same C4.4 machine list, so a search for "320 GC fuel filter" returns both. Second, Cat's description block on the 509-5694 page uses the fuel water separator wording, while the part title says Secondary Fuel Filter Element and the specification sheet says cartridge, out-to-in, 88.5 mm × 169 mm. When the copy and the spec sheet disagree in wording, trust the spec sheet and the dimensions.

The practical test when a supplier offers you one number for both positions: ask for the diameter. An 88.5 mm element will not seal in a housing machined for a 102.7 mm element, and the length difference — 169 mm against 258.3 mm — is visible with a tape measure in seconds.

The Machine List Is a C4.4 List, Not an Excavator List

509-5694 is not a 320 filter that happens to fit other things. It is the C4.4 platform element, and Cat's compatible-model list runs across machine families:

Machine family	Models on Cat's list for 509-5694
Excavators	320, 320 GC, 320 GX, 323, 323 GC, 323 GX, 325, 326, 326 GC, 330, 330 GC, 333, 333 GC, 335, 336, 336 GC
Forestry excavators	FM538, FM548, FM558 (plus 538, 548, 558, FM528 and FM528 LL under Forestry Products)
Wheeled excavators	M314, M315, M315 GC, M316, M317, M318, M320, M320 GC, M322, MH3026, MH3040
Wheel loaders	926, 930, 938, 950, 962
Motor graders	120 GC, 140, 140 GC
Material handlers	MH3022, MH3024, MH3032, MH3040
Mobile hydraulic power unit	330 MHPU
Industrial engine	C4.4

The two elements' lists are not identical, and that is worth knowing before you order a kit. 523-4987 carries a wider excavator list than 509-5694: it also names the 316 GC and the 340, 345, 345 GC and 350, it adds MH3050 and MH3250 material handlers and the 336MHPU and 340MHPU power units, and the forestry list includes the 568. So a 326 GC needs both numbers, while a 350 needs the separator number at least — check the machine's own parts book rather than assuming the pair always travels together.

What the Same Service Usually Also Needs

Cat's own "frequently bought together" block on the 509-5694 page is a decent description of a full service: 509-5694 with 523-4987 (the fuel pair), 322-3155 (engine oil filter element), 479-8989 and 479-8991 (primary and secondary engine air elements), 500-0957 or 580-5439 (cabin air filter). We stock the whole cluster for the Next Gen 320 / 323 GC / 326 GC family and quote it as one shipment, which is cheaper and simpler than four separate orders from four suppliers:

• Caterpillar 523-4987 — separator element, 102.7 mm × 258.3 mm, Ultra High Efficiency
• Caterpillar 322-3155 — engine oil filter element (cartridge)
• Caterpillar 479-8989 — primary air filter, Ultra High Efficiency, non-round
• Caterpillar 479-8991 — secondary air element that pairs with it

One Number Cat Prints Twice

Before you order the separator, look at the length. Cat's specification sheet for 523-4987 gives Length 10.169 in, which is 258.3 mm. The attribute line in the description block on the same page gives 250.3 mm (9.85 in). That is an 8 mm gap inside one Cat page, and it is the sort of difference that decides whether an element seats in the housing. We publish both figures rather than picking one and calling it settled, and we ask for a photo of the old element against a tape measure. If you are comparing a 250 mm and a 258 mm quote from two suppliers, measure yours — the answer is on your bench, not on the internet.

What We Do Not Publish

No price, because the honest variable is quantity, lane and whether you buy the pair or the full service set. No hour interval, because service intervals belong to the machine manual and the duty cycle — Cat's own maintenance-kit pages group intervals at 250, 500 and 1,000 hours by equipment type, and we will not convert that into a number for a machine we have not seen. And no claim that a cross-reference number is a guaranteed fit: catalogue cross lists are leads, and the two we can verify for 509-5694 (HIFI SN40859, SF-FILTER SK48942) also sit alongside a 103 mm diameter figure that belongs to the separator. Send the machine model with serial prefix, the numbers stamped on both old elements, and the diameters, and we come back with the pair, the seals and a price, shipped 3–7 days FOB Shanghai or CIF to your port.

FAQ

Q: What is Cat 509-5694?
A: 509-5694 is the secondary fuel filter element Cat lists for the Next Gen C4.4 machines — 320 GC, 320 GX, 323 GC, 326 GC, 330 GC and the rest. Cat's parts store publishes it as a cartridge, flow direction out-to-in, diameter 3.484 in (88.5 mm), length 6.654 in (169 mm), material polyamide plastic, with Meltblown media and glass-filled nylon end caps. It sits downstream of the separator element 523-4987 and is not interchangeable with it.

Q: Is Cat 509-5694 the same as Cat 523-4987?
A: No. They are two elements of one fuel system in different positions and different sizes. 523-4987 is the Element-Separator, Ultra High Efficiency, 4.043 in (102.7 mm) diameter and 10.169 in (258.3 mm) length; 509-5694 is the secondary fuel filter element, 3.484 in (88.5 mm) diameter and 6.654 in (169 mm) length. Cat's own wording for the separator line is that fuel water separators are built to extend the life of the secondary filter — the separator is upstream. An element that is 103 mm across does not go where an 88.5 mm element goes.

Q: Which machines does Cat 509-5694 fit?
A: On Cat's published compatible-model list: excavators 320, 320 GC, 320 GX, 323, 323 GC, 323 GX, 325, 326, 326 GC, 330, 330 GC, 333, 333 GC, 335, 336, 336 GC and the forestry excavators FM538, FM548, FM558; wheeled excavators M314, M315, M315 GC, M316, M317, M318, M320, M320 GC, M322, MH3026, MH3040; wheel loaders 926, 930, 938, 950, 962; motor graders 120 GC, 140, 140 GC; material handlers MH3022, MH3024, MH3032, MH3040; forestry 538, 548, 558, FM528, FM528 LL; mobile hydraulic power unit 330 MHPU; and the C4.4 industrial engine. The separator 523-4987 carries a wider list than this one, including 316 GC and the 340 / 345 / 345 GC / 350 excavators.

Q: What cross-reference numbers are quoted for 509-5694?
A: Two aftermarket catalogue numbers appear against 509-5694 in more than one catalogue: HIFI SN40859 and SF-FILTER SK48942. Those are catalogue equivalences, not proof of fit — catalogues also print a 103 mm outer diameter figure beside the 88–88.5 mm one, and 103 mm is the number Cat publishes for the separator element 523-4987. We quote Cat's own figures (3.484 in / 88.5 mm diameter, 6.654 in / 169 mm length) and confirm against the element you are replacing.