What oil should I put in my manual transmission?
The fluid you use should come from your vehicle’s manufacturer specifications. Most manual transmissions use a gear oil around 75W-90 or 80W-90 and labeled GL-4 or GL-5, or a dedicated manual transmission fluid (MTF). Always verify with the owner’s manual or dealer before filling.
Understanding what your transmission needs
Determining the right oil starts with the official specification and an awareness of your driving conditions. The following guidance helps translate labels into a practical choice.
To determine the right oil, consider these factors:
- Manufacturer specification: Check the owner's manual, the service bulletin, or the transmission dipstick/label for the exact fluid type (GL-4 or GL-5, MT fluid, and the viscosity).
- MTF vs gear oil: Some manuals call for a dedicated manual transmission fluid (MTF); others specify conventional gear oil. Do not substitute unless the manual explicitly allows it.
- Bringing in differential considerations: If the transmission shares oil with a limited-slip differential, you may need a fluid with friction modifiers compatible with LSD units.
- Climate and usage: Colder climates may benefit from a lighter viscosity (e.g., 75W-90), while high-load or hot environments can justify a thicker grade (e.g., 80W-90 or 75W-140 in some cases).
- Warranty and OEM guidance: Some warranties require OEM-approved fluids; deviating from the spec could affect coverage.
In practice, following the OEM specification is the safest path. If you cannot locate the manual, consult a dealership or a qualified technician to confirm the correct fluid.
GL-4 vs GL-5 and why it matters
Gear oils are rated GL-4 or GL-5 by the API, reflecting their extreme-pressure performance and compatibility with transmission components. The key difference is how aggressively they protect synchronizers and delicate metals inside the gearbox.
GL-4 and GL-5: what’s the practical difference?
GL-4 offers a balance that’s gentler on brass or copper synchronizers found in many manual boxes, reducing wear during shifting. GL-5 provides stronger extreme-pressure protection for gears under heavy load but can contain additives that may corrode brass synchronizers in some older or brass-lined components. Many modern oils are formulated as GL-4/GL-5 blends or specify which transmission they fit; always follow the carmaker’s recommendation.
MTF vs gear oil: when to choose which
Manual Transmission Fluid (MTF) is a fluid designed specifically for the moving parts inside a manual gearbox and sometimes differs in friction modifiers and viscosity from traditional gear oils. If your manual specifies MTFL or a particular MTF grade, use that exact fluid. If it specifies gear oil, use a GL-4 or GL-5 gear oil as appropriate. In general, do not substitute ATF unless the manufacturer explicitly allows it, since ATF has different properties and additives that may not suit a manual gearbox.
Practical guidelines by vehicle type
Different brands and generations of vehicles have varying specs. The following patterns are commonly seen, but always verify with your manual or dealer:
- Modern passenger cars with synchronized manuals often use 75W-90 GL-4 or GL-5, or a dedicated MTF specified by the manufacturer.
- Some Japanese and European manuals require an MT fluid (often in a viscosity around 75W-90 or similar) rather than traditional gear oil.
- Older or heavy-use transmissions (trucks, SUVs, performance cars) may call for 75W-140 or other heavier grades, especially in limited-slip applications.
When in doubt, choose the fluid exactly as specified by the vehicle’s manufacturer. Using the wrong oil can lead to stiff shifts, increased wear, or transmission damage.
Summary
Ultimately, the correct manual transmission fluid is the one specified by your vehicle’s maker. Commonly, this is a 75W-90 or 80W-90 gear oil meeting GL-4 or GL-5, or a dedicated MTF as directed by the manual. Watch for additives if you have a limited-slip differential, and avoid substituting ATF unless explicitly approved. If you cannot locate the spec, contact the dealer or a qualified technician to ensure you select the right fluid and maintain the longevity of your transmission.
What oil to use in a manual transmission?
Manual transmission fluid, like engine oil, is generally brown to amber in color. Commonly recommended manual transmission fluid formulations include SAE 80W, 75W-90, 80W-90 and SAE 90. In some cases, a multi-grade engine oil or automatic transmission fluid may be recommended.
Can you put 10W30 in a manual transmission?
However, motor oil does not contain the proper additives, and continued use can cause stiffer shifting. Replace as soon as it is convenient.” TLDR: 10w30 is fine temporarily, replace when you can.
Which oil is thicker, 75W90 or 80w90?
Yes, 80W-90 is thicker than 75W-90, particularly at colder temperatures. The "W" in the viscosity rating stands for "winter," and a lower number indicates better flow in the cold; 75W flows more easily when cold than 80W. At normal operating temperatures, both oils are rated as "90," meaning they have the same viscosity and provide similar protection.
Key differences
- Cold start-up: 75W-90 is thinner and flows to critical components faster during cold starts, providing better protection when the engine is cold. 80W-90 is slightly thicker in cold conditions.
- Operating temperature: When the engine is at its normal operating temperature, the "90" rating indicates that both oils have a similar thickness and provide the same level of protection for gears and bearings.
- Performance: While 80W-90 is more common in some older vehicles, many manufacturers now specify 75W-90 because its better cold-flow properties can reduce wear and improve fuel economy during start-up.
What is 80w90 gear oil used for?
80W-90 gear oil is a multipurpose, high-performance lubricant used in vehicle and machinery gearboxes, especially differentials and axles, where extreme pressure protection is needed. Its specific viscosity grade (80W−9080 cap W minus 9080𝑊−90) indicates it performs well in both cold (80W80 cap W80𝑊) and high (909090) temperatures, making it suitable for a wide range of applications and conditions.
Common uses for 80W-90 gear oil
- Automotive differentials and axles: This is a primary use, protecting hypoid gears that experience high pressure and sliding action.
- Light and heavy-duty trucks: It is suitable for the heavy-duty axles of trucks, which often handle heavy loads and towing.
- Industrial and heavy equipment: It is used in machinery like excavators, backhoes, and bulldozers.
- Agricultural machinery: It provides lubrication for tractors and other farm equipment operating under heavy loads.
- Manual transmissions: It can be used in some manual transmissions and transaxles that specify this grade and API GL-5 or GL-4 rating, but it is not recommended for gearboxes with "yellow metal" components.
Key benefits
- Extreme pressure protection: Contains additives that form a strong protective film on gear teeth to prevent metal-on-metal contact under high loads.
- Wide temperature performance: The "80W80 cap W80𝑊" indicates it flows well in cold temperatures, while the "909090" indicates its viscosity in hot temperatures, ensuring protection across different climates.
- Corrosion and rust prevention: Includes rust and corrosion inhibitors to protect internal components, especially in moist environments.
- Reduced wear and tear: Helps extend the life of components by reducing friction and wear.
