Kubota GL21 filters & filter set
Suitable for the entire Kubota GL series (Grandel): GL19, GL21, GL23, GL25, GL25K, GL26, GL27, GL29, GL32 and GL33 (also GL23DJ and GL27DJ, and the Hinomoto NX series NX19–NX32).
The Kubota GL21 has four filters: an engine oil filter, a fuel filter, an air filter and a hydraulic filter. All four are readily available, and the manual even lists the original part numbers. Below you'll find the interval, the OEM number for reference, and the corresponding dimensions for each filter.
Kubota GL21 filter overview with OEM numbers
| Filter | Interval | OEM number (for reference) |
|---|---|---|
| Engine oil filter (cartridge) | 1st after 50 h, then every 200 h | 17321-3243-0 |
| Fuel filter element | every 400 h (complete housing: when contaminated) | element 15521-4316-0, complete 15521-4301-0 |
| Air filter element | clean every 100 h, replace annually or after 6x cleaning | 15741-1108-0 |
| Hydraulic oil filter (cartridge) | 1st after 50 h, then every 200 h | 34680-3771-0 |
The OEM numbers apply to the entire series; when dealing with grey imports, always check the chassis number, as there are variations in specifications within the series.
Engine oil filter and fuel filter
The engine oil filter is a screw-on cartridge next to the engine block. Replace it every second oil change (200 hours), lightly lubricate the rubber ring with oil, and tighten it by hand. The fuel filter sits in a glass bowl under the fuel tap: replace the element (outer diameter 50 mm, inner diameter 20 mm, length 89 mm) every 400 hours, and rinse the bowl clean in between whenever you notice dirt or water. When changing it, close the fuel tap and then bleed the system afterwards – you can read how that works in the blog about troubleshooting.
Air filter: cleaning is fine, but not indefinitely
The dry air filter element (102 mm outer diameter, 66 mm inner diameter, 260 mm length) should be blown clean from the inside every 100 hours with low-pressure compressed air. Kubota is clear about this: after six cleanings or at most after one year, replace the element, even if it still looks reasonably good. A clogged air filter is recognisable by power loss and black smoke; a damaged element lets dust through, which will eventually damage the engine.
Hydraulic filter: the most often forgotten filter
Because the transmission, rear axle and hydraulics share a single oil system, the hydraulic filter also filters the oil that your gearbox and lift run on. Especially on older tractors with an unknown history, this filter has often never been replaced. When buying a tractor, make this part of the major service as standard: every 200 hours, together with fresh UDT-type oil as described in the blog about engine oil and fluids.
Everything in one go: the filter set
For the GL series, there's a complete set with oil filter, fuel filter, air filter and the copper sump plug gasket – exactly the parts needed for a 500-hour service in a single order. This is cheaper than ordering separately, and you're guaranteed that everything fits.
