Lubricant guide ·
Industrial gear oil ISO VG 220 vs 320: which does your gearbox need?
What the two grades mean, EP gear oil standards, when each is used, worm gearboxes, mixing, warning signs and good oil-change practice.
Walk through a machine shop or foundry in Shapar-Veraval and you will find enclosed gearboxes everywhere: on conveyors, mixers, cranes, extruders and machine drives. Most of them run on an EP industrial gear oil in ISO VG 220 or 320. The two grades are easily confused, and the wrong one shortens gear and bearing life.
What ISO VG 220 and 320 mean
The ISO VG number is the oil's kinematic viscosity in centistokes (cSt) at 40°C, within ±10%. ISO VG 220 is therefore about 198–242 cSt and ISO VG 320 about 288–352 cSt. That makes VG 320 roughly 45% thicker than VG 220 at the same temperature. Neither is "better". Each suits a different combination of load, speed and temperature.
EP gear oils and the standards on the label
Enclosed industrial gearboxes normally need an extreme-pressure (EP) gear oil, to DIN 51517 Part 3 (CLP) or AGMA 9005 EP. EP additives protect the gear teeth under heavy and shock loads. In older AGMA terms, VG 220 corresponds roughly to AGMA 5EP and VG 320 to AGMA 6EP, which helps if an old gearbox plate gives an AGMA number.
Don't substitute an automotive gear oil (such as an 80W-90 GL-5) in an industrial gearbox unless the gearbox maker approves it. Its additives are designed for vehicle axles and can be too aggressive for the bronze worm wheels found in many industrial boxes.
When 220, when 320
| Grade | Usually used for |
|---|---|
| ISO VG 220 | Most enclosed helical and bevel gearboxes at moderate speeds and temperatures, such as conveyor drives, mixers and general machine drives. |
| ISO VG 320 | Heavier loads, slower speeds, higher ambient or operating temperatures, and many worm gearboxes. |
The rule of thumb is that slower gears and heavier loads need thicker oil, while faster gears need thinner oil. Heat matters too. A gearbox in a foundry, or next to a furnace in a Rajkot summer, runs hotter, and the gearbox maker may call for a heavier grade at high ambient temperatures. The nameplate or manual is the final word. Many plates state the grade directly, as in "ISO VG 320 CLP", or give a lubricant table by ambient temperature.
Worm gearboxes
Worm gearboxes have a lot of sliding contact and run hotter than helical boxes. They typically need a heavier oil, often VG 320, and some need VG 460 or higher. Some makers specify a synthetic oil (PAO or PAG). PAG oils must never be mixed with mineral oils. The worm wheel is usually bronze, so use a gear oil the maker approves for it. Check the plate.
Don't mix grades or types
Topping up a 220 gearbox with 320, or the other way round, leaves you with an in-between viscosity that neither the gearbox nor the oil was designed for. Mixing mineral and synthetic oils, especially PAG, can cause foaming and deposits. If you are changing grade or type, drain the box while it is warm, flush it if needed and refill.
Signs the grade or the oil is wrong
| Symptom | Possible cause |
|---|---|
| Running hotter than usual | Wrong grade (too thick churns and heats, too thin lets metal touch), wrong oil level, or worn-out oil. |
| Rising noise or whine | Oil too thin for the load, low oil level, or wear in the bearings or gears. |
| Pitting or scuffing on the teeth | Oil too thin, or lacking EP protection for the load, or contaminated. |
| Foaming or milky oil | Water in the oil, mixed oils, or overfilling. |
Changing and topping up
Check the level with the gearbox stopped, on the sight glass or dipstick, and top up with the same oil. Change it on the maker's interval, which often includes a first change after running-in, or by oil analysis. Change it sooner if the oil darkens badly, smells burnt, or shows water or metal particles. Drain it while warm so the contaminants come out with the oil. Keep breathers clean too: a blocked breather pressurises the box and pushes oil past the seals.
EP gear oils we stock in VG 220 and 320
These are EP industrial gear oils we stock in the two grades. Castrol Optigear Synthetic A 320 and Shell Omala S4 GXV Plus 320 are synthetic, so check compatibility before using them to top up a box that holds mineral oil. We are a multi-brand retailer, not an authorised dealer of any of these brands.
Buying industrial gear oil in Rajkot
Our shop is at Tilara Gate, near the Shapar Veraval Industrial Association. Regular customers in Shapar-Veraval get same-day delivery (a minimum order applies). We also deliver to Metoda GIDC and across Rajkot, with timing confirmed per order. Every order comes with a GST bill, and factories get a bulk discount. Send us the grade on your gearbox plate, or a photo of the plate itself, on WhatsApp. See all the industrial gear oils we stock.
