By Lukeron Lubricants · Last updated
Quick answer
The SAE number on gear oil shows how thick it is, and it is not the same scale as engine oil. 80W-90 is the usual choice for car and light truck axles. 85W-140 is thicker, for heavy-duty axles and hot, heavily loaded work. EP-90 and EP-140 are single-grade oils for gearboxes whose makers name SAE 90 or 140. GL-5 is the API level for hypoid axles. Tractors use a separate tractor transmission oil, and scooters use the small-fill oil named in the manual. The manual decides.
Common gear oil grades and where they fit
| Grade | Usually used for | Lukeron product |
|---|---|---|
| 80W-90 GL-5 | Car, SUV and light truck axles and differentials, when the maker names it | SPL Gear Oil EP 80W-90 GL-5 |
| EP-90 GL-5 | Gearboxes and axles whose maker names SAE 90 | SPL Gear Oil EP, EP-90 GL-5; ECO Gear Oil EP-90 |
| 85W-140 GL-5 | Heavy-duty truck and bus axles, heavy load, hot weather | SPL Gear Oil EP 85W-140 GL-5; SPL Rota Gear Oil EP 85W-140 |
| EP-140 GL-5 | Heavily loaded gears whose maker names SAE 140 | SPL Gear Oil EP, EP-140 GL-5 |
| UTTO 20W | Tractor transmission, hydraulics and wet brakes | SPL UTTO 20W Universal Tractor Transmission Oil |
General guidance only. Follow the vehicle or machine maker's manual for grade and API level.
Walk into any spares shop and you will see gear oil in 80W-90, EP-90, 85W-140 and EP-140. The numbers look like engine oil grades, but they are not. This guide explains what each gear oil grade means, where each one is normally used, and how to choose without guessing.
What the numbers on a gear oil mean
The SAE number tells you how thick the oil is. Gear oil and engine oil use different scales, so an 80W-90 gear oil is not the same as a 20W-40 engine oil, and you cannot swap one for the other. A bigger number means a thicker oil, so 140 is thicker than 90.
The letter W stands for winter. A multigrade such as 80W-90 flows like an 80W oil when the gearbox is cold, so it reaches the gears quickly, and it protects like a 90 oil when the gearbox is hot. A single-grade oil such as EP-90 is an SAE 90 gear oil that keeps its grade at all temperatures.
What EP and API GL-5 mean
EP stands for extreme pressure. Gear teeth press hard against each other, and EP gear oil carries additives that protect the metal under that load. Almost every automotive gear oil you buy for axles and differentials is an EP oil.
API GL-4 and GL-5 are service levels. GL-5 carries more extreme pressure additive than GL-4 and is made for hypoid gears, such as the rear axle of a truck or car, under heavy load and shock. GL-4 is a milder level that some manual gearboxes call for. Use the level your manual names. Some manual gearboxes with brass synchronizer rings ask for GL-4 and do not accept GL-5.
Which gear oil grade for which job
- 80W-90 GL-5: car, SUV and light truck rear axles and differentials, and manual gearboxes only when the manual names it.
- 85W-140 GL-5: heavy-duty axles of trucks and buses, heavy loads and hot weather, where the maker calls for a thicker oil.
- EP-90 and EP-140: single-grade gear oils for gearboxes and axles whose makers name SAE 90 or SAE 140, often older or commercial vehicles.
- Tractor transmission oil: tractors often use one oil for the gearbox, hydraulics and wet brakes. That is a universal tractor transmission oil (UTTO), not EP-90.
- Industrial gearboxes: these use ISO VG grades such as EP 220 and EP 320, not SAE grades.
- Scooters and motorcycles: the gear case has its own small fill. The maker names the grade.
Gear oil for scooters and motorcycles
Many scooters have a small gear case, also called the final drive, with its own gear oil. The fill is small, often only a few hundred millilitres, and the maker names the grade. It is often lighter than the oil used in a car or truck axle, so do not assume 80W-90. Read the owner's manual or ask the dealer, and use the grade it names. Our guide on GL-4 and GL-5 for motorcycles explains the service levels in more detail.
Why gear oil prices differ
Two bottles that look alike can cost very different amounts. The price depends on the grade, the API level, whether the base oil is mineral or synthetic, the quality of the additive package, and the pack size. A 20 litre bucket or a 210 litre drum costs less per litre than a 1 litre bottle. GST is added on top. Because base oil and freight costs move, we quote the current price for your grade, pack and quantity. Send us those three details and we reply within 1 to 2 business days.
Mistakes to avoid
- Using engine oil in a gearbox or axle, or gear oil in an engine.
- Thinking a thicker oil is always better. Too thick an oil can make shifting stiff in cold weather.
- Putting GL-5 in a manual gearbox that asks for GL-4.
- Changing the grade without checking the manual or the maker.
- Overfilling or underfilling. Fill to the level plug.
How to choose in four steps
- Read the manual or the nameplate for the SAE grade and the API level.
- Match both. Do not use a different grade because it is cheaper or easier to find.
- Check the climate and the load. A hot climate and a heavy load are what 85W-140 and EP-140 are for, if the maker allows them.
- If the manual is not available, send us the vehicle or machine and model and our team will help you choose.