Caterpillar 479-8991 Air Filter (Secondary Element)

The Element Nobody Puts on the Order

479-8991 is the second half of the air cleaner on the current 320 family, and it is the half that gets left off the purchase order. The primary element 479-8989 is the obvious purchase: it is the big element, it is the one the restriction indicator is about, and it is the one an operator can change by hand. The secondary element sits behind it, hidden, flat, and easy to believe is still fine. On a machine working in dust that belief is expensive, because the secondary is the only thing between the intake and the cylinders during the minutes the primary is out of the housing — and the only filter in the system if a primary ever splits at a seam.

Caterpillar's parts store lists it plainly as the secondary standard-efficiency element, and its own "frequently bought together" pairing for 479-8989 puts 479-8991 next to it, which is the cleanest statement available of what belongs in one order. The 320 / 320 GC / 323 parts reference guide does the same, listing 479-8989 and 479-8991 side by side under engine air filters against the ZBN, DKJ, YBL and RAZ serial prefixes; the companion guide covering the HEX, MYK, KTN and LKS prefixes lists the same pair.

Service It by the Book: Never Clean, Replace

The handling rule is short and it is Cat's own: a secondary element should never be cleaned, and should be replaced every third primary element change or as required. Knocking it out or blowing it off with compressed air does not reset it — it pushes the retained dust deeper into the media, and the element goes back into the housing looking serviced while performing like a loaded one. That is the version of this failure that shows up as unexplained dust ingestion three months later, with everything on the machine apparently correct.

When the "or as required" case arrives is a function of the site, not of the calendar. On quarry haul roads, demolition and mining benches, the primary loads faster and therefore gets changed more often, so the third-change trigger comes around sooner. Operators running a 320 GC or a 323 on that kind of duty should carry one 479-8991 in the store for every three primary elements, and treat the restriction indicator as the honest second opinion.

Dimensions, and Why We Print Cat's Figures

Cat publishes 479-8991 as 6.811 in (173 mm) wide, 2.559 in (65 mm) deep and 14.055 in (357 mm) high, non-round, in standard-efficiency media with a polyurethane end. Aftermarket listings for the same element are close on width and depth but do not all agree on length — at least one supplier catalogue quotes its own version at 385 mm long against Cat's 357 mm. We publish Cat's figures, note where the independents diverge, and confirm against the element you are holding rather than declaring one number infallible. A safety element that is 28 mm too long does not seat, and a safety element that does not seat is worse than a dirty one.

Cross References and the One We Refuse to Print

Two numbers for 479-8991 appear across several independent catalogues and we publish both: SA160067, which different catalogue books index under HIFI and under Sakura, and WIX WA11220. For the primary element, 479-8989, the multi-source numbers are SA160066, SF-FILTER SL82517 and WIX WA11217.

What we do not print is the Fleetguard number that circulates with this element. It appears on a single supplier page rather than in catalogue-level data, and Fleetguard's own reference material places that number against a different element entirely — a panel filter of roughly 175 × 223 mm sold for AGCO, Cummins and Doosan applications. Someone assembling a filter list from copied pages will order that number for a 320 and receive a filter that fits nothing on the machine. We would rather show a gap in the table than fill it with a number that reads convincingly and costs a week.

Ordering the Pair, and What We Do Not Publish

No servicing interval, because Cat sets it per machine group, serial range and duty cycle, and the dustier the site the shorter the honest answer. No fixed price, because media grade, quantity and freight move the number — we quote against the grade and quantity you need. And no claim that this element covers the whole 320 family: the 320B to 320D machines run the round 131-8822 with 131-8821 behind it, and the 320D2, 320E and 323E generation runs the round 528-7222, so the air cleaner housing decides which family you are in.

Send the number off your air cleaner group, or a photo of the two elements side by side with a tape measure across the old primary, and we confirm the pair, quote both, and dispatch in 3–7 days — FOB Shanghai or CIF to your port.

FAQ

Q: What is Cat 479-8991?
A: 479-8991 is the secondary engine air filter element Caterpillar lists behind the primary element 479-8989 on the current generation of 320-class machines. Cat's parts store names it Secondary Standard Efficiency Engine Air Filter and lists it for the 320, 320 GC, 320 GX, 323, 323 GC, 323 GX, 324, 325, 326, 326 GC, 333 GC and 335 excavators, the M317 to M323 wheeled excavators, D4 and D5 dozers, FM528 and FM528 LL forestry machines and the 120 motor grader. Cat publishes it as a non-round element in standard media, 6.811 in wide, 2.559 in deep and 14.055 in high.

Q: Do I have to replace 479-8991 when I change the primary filter?
A: Not at every change, but on a schedule you should not guess. Cat's own filters guidance says a secondary element should never be cleaned and should be replaced every third primary element change or as required. On a machine working in quarry, demolition, mining or construction dust — the duty the 479-8989 UHE primary was designed for — the required case arrives sooner, and the restriction indicator is the signal that it has. What the secondary element must never be is reused dirty: blowing it out drives the retained dust through the media.

Q: Which is the primary and which is the secondary on the current Cat 320?
A: 479-8989 is the primary, the large non-round ultra-high-efficiency element you lift out first, quoted by Cat at 7.992 in wide, 11.693 in deep and 15.315 in high. 479-8991 is the secondary, the much flatter standard-efficiency element that sits behind it, quoted at 6.811 in wide, 2.559 in deep and 14.055 in high. Caterpillar's own parts store lists the two together against the same machines, and the 320 / 320 GC / 323 parts reference guide lists both against the ZBN, DKJ, YBL and RAZ serial prefixes.

Q: What are the cross reference numbers for 479-8991?
A: Two numbers appear across several independent catalogues: SA160067, indexed as HIFI in some catalogue books and Sakura in others, and WIX WA11220. We publish those and stop there. Other numbers circulate with this element on single supplier pages — including one Fleetguard number that Fleetguard catalogue data places against a completely different panel element for AGCO, Cummins and Doosan applications — and we will not print a cross reference that we cannot confirm in more than one source, because a wrong air filter number is a machine standing still.