Choosing the right gear oil is one of the most overlooked decisions in vehicle maintenance, yet it directly affects how long your gearbox, axle and differential last. In the Indian market two grades dominate: 80W90 and 85W140. Both are extreme-pressure (EP) gear oils and both protect gears under heavy load, but they are engineered for very different jobs. Pour the wrong one in and you can end up with noisy gears, premature wear or poor cold-morning shifting. This guide explains what the numbers mean and how to choose the grade your vehicle actually needs.
What the numbers on a gear oil actually mean
Gear oil grades follow the SAE J306 viscosity standard. The number before the “W” (which stands for winter) describes how the oil flows when cold — a lower number means better flow at low temperatures. The number after describes viscosity at operating temperature, where a higher number means a thicker protective film when hot. So 80W90 stays fluid in cold weather and delivers a 90-weight film at heat, while 85W140 is a little stiffer when cold and much thicker — a 140-weight film — at high temperature. Both grades are typically fortified with EP additives that form a sacrificial layer on the gear teeth to survive the crushing, sliding loads inside an axle or differential.
80W90 gear oil: the everyday all-rounder
80W90 is the most widely used automotive gear oil in India. Its balanced viscosity makes it ideal for manual transmissions, differentials and axles in passenger cars, SUVs, jeeps, tractors and light commercial vehicles running under normal to moderately heavy loads. Because it flows well when cold, it gives smoother gear engagement on winter mornings and in hill-station temperatures. For most fleet cars, pickups and farm equipment operating in typical Indian conditions, an API GL-5 80W90 is the default recommendation.
85W140 gear oil: built for heat and heavy loads
85W140 is a heavy-duty grade. Its much thicker high-temperature film is designed for hypoid differentials and axles in fully loaded trucks, buses, trailers, construction machinery and off-road equipment that run at sustained high temperatures under crushing loads. In the peak of an Indian summer or on long highway hauls, a thinner oil can shear and lose its protective film — 85W140 holds up. The trade-off is slightly stiffer flow when cold and marginally higher drag, which is why it is not recommended for light vehicles that simply do not need it.
80W90 vs 85W140: the quick comparison
| Factor | 80W90 | 85W140 |
| Cold flow | Better (thinner when cold) | Stiffer when cold |
| Hot film strength | Good for moderate loads | Higher, holds up under heat |
| Typical vehicles | Cars, SUVs, LCVs, tractors | Heavy trucks, buses, off-road |
| Load rating | Moderate to heavy | Very heavy / sustained |
| Best climate | All-round, incl. cold starts | Hot, high-stress operation |
How to choose the right grade
Always start with your vehicle’s owner manual or OEM specification. The manufacturer states both the SAE grade and the API service level (GL-4 or GL-5). GL-4 suits many manual synchromesh gearboxes, while GL-5 is for hypoid differentials under high load — and confusing the two can damage soft-metal synchros. Beyond the manual, weigh three factors: load (heavier and constant loads favour 85W140), temperature (hotter, sustained operation favours 85W140), and climate (very cold starts favour the easier flow of 80W90). For a mixed fleet in doubt, an 80W90 GL-5 covers the widest range of light and medium vehicles.
Common mistakes to avoid
Do not assume thicker is always better: over-thick oil in a light gearbox increases drag and can hurt fuel economy and cold shifting. Do not use a GL-5 oil where the manufacturer specifies GL-4 for a synchromesh box. And do not top up with a random grade, since mixing very different viscosities dilutes the protection you paid for. If you manage a fleet, standardising on the right two grades — typically an 80W90 for lighter vehicles and an 85W140 for heavy haulers — keeps your stores simple and mistakes rare.
The bottom line
Both 80W90 and 85W140 are proven EP gear oils; the right choice comes down to load, heat and what your OEM specifies. Petroblast manufactures both grades in GL-4 and GL-5 formulations as part of its full gear oil range, supplied in retail packs and in bulk for workshops, fleets and distributors across Delhi NCR and the rest of India. If you are unsure which grade suits your vehicles or need bulk gear oil supply, our team can help you match the correct specification.