Which Gear Oil? ISO 220 or 80W-90, GL-4 or GL-5 Made Simple

The gearbox plate says ISO VG 220, the handbook wants 80W-90 GL-5, and the drum says CLP. Match the grading system first, then the exact grade and specification.

PartsForMachines lists 22 gear oils from Q8, Shell, Castrol, HyperDrive and Fuchs in its Gear Oil range. They come in 20-litre packs and drums, from industrial ISO VG 68 to 460 grades to 75W-90 and 80W-90 GL-5 axle oils.

ISO 220 or 80W-90: Can One Gear Oil Replace the Other?

Not unless the machine maker approves it: the two systems grade oils differently. An ISO VG number reflects viscosity at 40°C, so the Omala S2 GX 220 industrial gear oil (550041650) measures 220 mm²/s. SAE gear grades are set at 100°C, with a separate W rating for cold flow.

Industrial oils carry codes such as DIN 51517 Part 3 CLP or ISO 12925-1 CKD, while axle oils carry API GL ratings. So choose an industrial gearbox’s oil by its ISO grade and type, and give an axle or final drive the SAE grade and GL rating its handbook names.

GL-4 or GL-5: Can GL-5 Harm a Gearbox That Asks for GL-4?

It can in some gearboxes, so use the category the handbook names. GL-4 covers synchromesh manual gearboxes, where moderate extreme-pressure (EP) additive levels are enough. GL-5 carries more EP additive, for hypoid axles and final drives that take heavier shock loads.

That extra additive can attack the soft yellow metals used in some gearboxes. A GL-4 oil, in turn, gives hypoid gears less protection. If GL-5 has gone into a GL-4 box, drain and refill with the specified oil.

Can I Use 80W-90 Where the Manual Says SAE 90?

Usually, yes, as long as the GL rating matches. An 80W-90 is a multigrade: it meets the SAE 90 range at working temperature and flows like an 80W grade when cold. A 75W-90 is the same SAE 90 grade when hot, but its cold-flow limit is -40°C against -26°C for an 80W, so it flows better from cold.

Where hypoid final drives or spiral-bevel axles call for 80W-90 GL-5, the KX+ 80W-90 GL-5 gear oil is a mineral multigrade option that also suits steering gearboxes.

Can I Top Up With a Different Brand of Gear Oil?

It is safer not to: where you can, top up with the oil already in the gearbox. Oils of the same grade can use different additive chemistry, and mixing them can make those additives less effective. Polyglycol (PAG) synthetic gear oils should not be mixed with mineral oils.

If you cannot get the same oil, match the grade, specification and base oil type, and check with the oil maker that the additives are compatible. For axles, HyperDrive says the KXR 75W-90 fully synthetic gear oil can top up wherever 80W-90 is specified.

What Should I Check Before I Buy Gear Oil?

• the grading system on the plate or in the manual: an ISO VG grade with CLP, CKD or an AGMA number, or an SAE grade with an API GL rating
• the exact grade, such as ISO VG 220 or SAE 80W-90, and the GL-4 or GL-5 category
• any gearbox maker approval named, such as Siemens for Flender gear units
• the oil already in the gearbox, if you are topping up
• the pack size: a 20-litre pack, or a drum of 199 to 209 litres for workshop bulk use

Not sure what your gearbox needs? Contact the PartsForMachines team by WhatsApp, telephone or email with the machine or gearbox make and model and a photo of the plate, or browse the Gear Oil range.

Pack sizes, delivery options and returns terms are shown on each product page. A 30-day return policy applies to eligible items.

Frequently Asked Questions

My manual says AGMA 5EP or names an old oil: what do I buy?

Match the ISO grade. The Alpha SP 220 gear oil lists AGMA 5EP alongside ISO VG 220, and the same range pairs 4EP with 150 and 6EP with 320. For an obsolete oil, find its ISO grade and type, such as CLP, and match both.

Which ISO grade does an industrial gearbox need?

Whatever the nameplate or manual says: the maker sets it for gear geometry, speed, load and ambient temperature. Faster, lighter units take lower grades, such as the Omala S2 GX 68 gear oil; slow, heavily loaded drives take higher ones, such as ISO 460.

What do CLP and EP mean on an industrial gear oil?

CLP is the DIN 51517 Part 3 code: C for circulating oil, L for anti-corrosion and anti-oxidation additives, and P for extreme-pressure (EP) additives, which carry heavy tooth loads. The FZG rig tests load capacity; the Alpha SP 320 is rated above load stage 12.

Can one gear oil meet both GL-4 and GL-5?

Yes. Some universal 75W-90 and 80W-90 oils are made for both synchromesh gearboxes and hypoid axles and list both categories. Choose one only if the label shows the category your handbook asks for. These dual-rated oils sit in our transmission oil range.

What oil goes in mini digger final drives?

Whatever the operator’s manual names for the final drives (travel motors). Do not assume an industrial EP 220 or a standard 80W-90 will suit: check the grade and GL rating first, and send our team the machine model if the manual is missing.

Is synthetic gear oil worth the extra cost?

It can be, if the manual allows it. The fully synthetic KXR 75W-90 gives better cold starts and lower gear friction than mineral 80W-90 grades, and its synthetic base supports longer drain intervals. Synthetic oil makes most sense in extreme temperatures and hard-worked drives.

Is a heavier gear oil better for an old or leaking gearbox?

Not as a rule: use the grade the manual names. SAE sets the 85W cold-flow limit at -12°C, against -26°C for 80W, so an 85W-140 is stiffer from cold than an 80W-90. Leaking seals need replacing; if the wrong grade went in, drain and refill.

My tractor manual quotes J20C or M1143: do I need gear oil?

Not for parts that name them: those need a universal tractor transmission oil (UTTO). Spirax S4 TXM 10W-30, in our hydraulic oil range, lists both and is made for tractor transmissions, hydraulics and oil-immersed brakes. Check whether the front axle and hubs share that oil.

Can industrial gear oil go in a worm gearbox?

Only where the gearbox maker allows it. The Alpha SP range suits spur and helical gears, and it may be used in some worm gears that are lightly loaded. For other worm drives, follow the gearbox maker’s recommendation.

How should I store gear oil packs and drums?

Keep packs sealed in the original packaging, somewhere clean, dry and away from temperature extremes. Lay a drum on its side with the bungs at 3 and 9 o’clock, ideally under cover, so the seals stay tight and damp is not drawn in.