API GL-4 and API GL-5 are gear oil classifications defined by the American Petroleum Institute. They are formulated for different levels of load-bearing stress and different mechanical components. Using one where the other is specified can cause damage.
Key Takeaways
- GL-5 contains double the extreme-pressure additives for high-load differentials, but these chemicals will corrode bronze/brass synchronizers in GL-4 manual gearboxes.
- Using GL-4 in a GL-5 hypoid axle causes accelerated gear scoring, while using GL-5 where GL-4 is specified leads to shifting failure.
- You must match both the API chemistry (protection) and SAE viscosity (thickness); meeting one while ignoring the other risks mechanical seizure or film breakdown.
In This guide:
Recommended API GL-4 and GL-5 Gear Oils
The products listed below are popular options for different vehicles. Always check your owner’s manual first to make sure the oil’s chemistry and thickness are safe for your specific gears.
We listed products that range from small bottles for simple passenger car top-offs to buckets for commercial fleets or massive agricultural gearboxes.
Lucas Oil SAE 80W-90 Gear Oil
Lucas Oil GL-4 SAE 80W-90 Heavy Duty Gear Oil
Lucas Oil SAE 80W-90 Gear Oil is a GL-5 gear oil for differentials and axles in light trucks, SUVs, and 4x4s. The MT-1 rating makes it suitable for manual transmissions where most GL-5 oils are not.
Quick Specs
- Viscosity: 15.0 cSt @ 100°C
- Pour point: -36°C (-33°F)
- Flash point: 430°F
- Color: Clear light amber
The MT-1 certification is what separates this from a standard GL-5 axle oil. MT-1 indicates the formula is compatible with synchronizer materials, which standard GL-5 additives can damage. It also includes a friction modifier, so no separate additive is needed for limited slip differentials.
Lucas Oil SAE 80W-90 Gear Oil is for owners running a 4×4 with both a hypoid rear axle and a manual transmission, this covers both without needing two different fluids.
- Also meets: SAE J2360, MIL-PRF-2105E, MACK GO-J, PG-2 Limited Slip
PennGrade 1 Multi-Purpose Classic Gear Oil GL-4 SAE 80W-90
Penn Grade 1, GL-4 Gear Oil SAE 80W-90
PennGrade 1 Multi-Purpose Classic Gear Oil is formulated specifically for classic manual transmissions with yellow metal components. This is a mineral-based oil for gearboxes where GL-5’s EP additives would damage bronze, brass, or copper synchronizers.
Quick Specs
- Viscosity: 15 cSt @ 100°C / 138.3 cSt @ 40°C
- Viscosity index: 102
- Pour point: -27°F (-33°C)
- Flash point: 450°F (232°C)
Classic manual transmissions (like Muncie, Borg-Warner, Saginaw, Ford Toploader) were designed around GL-4 chemistry. Using GL-5 in these boxes risks glazing the synchro cones. This oil contains no friction modifiers, which is intentional: friction modifiers interfere with synchronizer engagement in these older designs.
For owners of classic American muscle, vintage imports, or older commercial trucks running Nissan UD, Mitsubishi Fuso, Volvo, or Mercedes manual transmissions that specify GL-4.
- Not for use in limited slip differentials
- Not suitable where GL-5 or OEM-specific fluids are required
Sta-Lube API GL-4 Multi-Purpose Gear Oil 85W-90
CRC Sta-Lube API/GL-4 Multi-Purpose Gear Oil 85W90
A GL-4 mineral-based gear oil for standard transmissions, transaxles, and differentials in cars, trucks, and buses. It is yellow-metal safe, making it suitable for vintage manual transmissions with bronze or copper synchronizers.
Quick Specs
- Viscosity: 17 cP @ 100°C / ISO VG 220
- Pour point: 15°F
- Flash point: 302°F to 360°F
- Specific gravity: 0.88 to 0.90
This oil covers both GL-3 and GL-4 requirements, which makes it practical for older equipment where GL-3 was the original spec. The EP additive package handles both automotive gear sets and industrial worm gears without being aggressive toward soft metals.
Sta-Lube is for owners of older vehicles, vintage trucks, or industrial equipment requiring GL-3 or GL-4 performance that’s compatible with yellow metal.
- Also meets: Mil-PRF-2105, US Steel 224, AGMA 250.06, AGMA 4EP
- Not suitable where GL-5 is required
Amalie Elixir Full Synthetic GL-5 85W-140
AMALIE Elixir Synthetic GL-5 75W-85W-140
Amalie Elixir Full Synthetic GL-5 85W-140 is a full synthetic GL-5 limited slip gear oil that works for light passenger cars through heavy commercial axles. The MT-1 rating extends its use to compatible manual transmissions.
Quick Specs
- Viscosity: 27.0 cSt @ 100°C / 180.0 cSt @ 40°C
- Viscosity index: 190
- Pour point: -42°C (-43.6°F)
- Flash point: 220°C (428°F)
- Brookfield viscosity @ -40°C: 100,000 cP
It functions as a 85W in cold starts and holds 140-weight film strength at full operating temperature. This makes it practical for mixed fleets or equipment that sees wide temperature swings without switching fluids. Limited slip additives are built in, so no separate treatment is needed.
Amalie Elixir Full Synthetic GL-5 85W-140 is for fleet operators, commercial truck owners, or anyone running equipment with multiple OEM-specific gear oil requirements across a single drivetrain.
- Also meets: Arvin Meritor 0-76-E/N/B/Q/R, Dana/Spicer SHAES 256 Rev C, Ford M2C119A/M2C154A, Eaton 500,000/750,000 Extended Drain, Mack GO-J/GO-J Plus, MAN 342 Type M-2, Scania STO 2:0, ZF TE-ML 05B/07A/08/12L/12N/16F/17B/19C/21B, Mil-PRF-2105E, SAE J2360
Presidential 80W-90 Gear Oil GL-5
Presidential 80W-90 Gear Oil GL-5 – Industrial Gear Lubricant
A GL-5 gear oil for industrial and mobile equipment applications requiring 80W-90 viscosity. Limited technical data is publicly available for this product.
Quick Specs
- SAE grade: 80W-90
- ISO VG equivalent: approximately 150 to 220
- Type: Mineral-based industrial gear lubricant
- Origin: Made in USA
Presidential is a Martin Lubricants brand produced under ISO 9001 quality standards. The 80W-90 GL-5 formulation covers high-load industrial gear systems where extreme pressure protection and foam resistance are the primary requirements.
TRIAX Gear Premium LS GL-5
TRIAX Gear Premium LS 85W-140, GL-5 Limited Slip Ready
A full GL-5 limited slip gear oil available in three grades: 80W-90, 85W-90, and 85W-140. It can work with vehicles from light passenger vehicles through heavy commercial and off-highway equipment. MT-1 rated across all grades.
Quick Specs (80W-90 / 85W-90 / 85W-140)
- Viscosity @ 100°C: 15.1 / 15.3 / 27.0 cSt
- Viscosity @ 40°C: 139 / 153 / 367 cSt
- Pour point: -36°C / -36°C / -15°C
- Flash point: 212°C / 216°C / 206°C
- Viscosity index: 109 / 100 / 106
This fluid is recommended for on-highway truck and bus operators, off-highway equipment running GL-5 or MT-1 fluids, and anyone maintaining limited slip axles who wants one fluid across multiple grades without separate LS treatment.
- Also meets: Arvin Meritor 0-76-A/B/D/M/N/Q, MB 235.0/235.1/235.5/235.6/235.8/235.20, ZF TE-ML 02A/B, 05A/B/C4, 07A, 08, 12A/B/C4/E, 16A/B/C/D/E4/F, 17A/B, 19A/B/C, 21A/B, Mack GO-J, MAN 341/342, Volvo 97310/1273.10, Scania STO 1:0/2:0A, Eaton, Ford WSP-M2C197-A, MIL-PRF-2105D/E, SAE J2360, NATO O-226
Amalie Hypoid Gear Multi-Purpose GL-5 85W-140
Amalie API GL-5 Certified 85W-140 Hypoid Multi-Performance Gear Oil
A GL-5 gear oil for light and heavy-duty axles, gearboxes, and transaxles requiring 85W-140 viscosity. Please note that this fluid has no MT-1 rating. This means that Amalie Hypoid Gear Multi-Purpose GL-5 85W-140 is an axle-focused fluid, not for manual transmissions.
Quick Specs
- Viscosity: 28.0 cSt @ 100°C / 380.0 cSt @ 40°C
- Viscosity index: 100
- Pour point: -15°C (5°F)
- Flash point: 265°C (509°F)
- Brookfield viscosity @ -12°C: <80,000 cP
Amalie Hypoid Gear Multi-Purpose GL-5 85W-140 is for operators of light and heavy-duty trucks or equipment with final drives and transaxles that specifically call out GL-5 85W-140, particularly in warmer climates or controlled-temperature environments.
- No limited slip additive. Separate LS treatment required for limited slip differentials
- Not suitable for manual transmissions without confirmed synchronizer compatibility
Motul Gear Competition 75W-140
Motul Gear Competition GL-5 1L
A GL-5 ester-based full synthetic gear oil built for racing applications; this includes limited slip differentials, synchronized and unsynchronized gearboxes, and transfer cases operating under shock loads.
Quick Specs
- Viscosity: 24.7 cSt @ 100°C / 170.0 cSt @ 40°C
- Viscosity index: 178
- Pour point: -36°C (-33°F)
- Flash point: 212°C (413°F)
- Color: Blue
Motul Gear Competition 75W-140 works best for racing applications or any high-performance street build running a limited slip differential under sustained high-load conditions.
- Approved: MUGEN Le Mans 24H, Hewland, X-TRAC Japanese GT
- Not a daily driver fluid. Change intervals should follow manufacturer requirements and be adjusted based on actual use conditions
Oils That Meet Both GL-4 and GL-5
Some gear oils mentioned above are formulated to meet both GL-4 and GL-5 performance requirements. These are commonly called universal gear oils.
Universal gear oils use sulfur-phosphorus additive packages capable of satisfying the requirements of both grades. They were developed to cover applications that sit between the two classifications: hypoid axles in passenger cars, which require GL-5 protection, and spiral bevel rear drives in trucks, which are typically satisfied by GL-4.
In agriculture, Super Tractor Oil Universal (STOU) fluids take this further. A single STOU fluid is designed to lubricate the engine, gearbox, and axles of a tractor.
For the gearbox and PTO, these oils meet GL-4 requirements. For heavy-duty front axles, such as ZF units that specify GL-5, advanced STOU formulations have been tested to perform at a comparable level to GL-5 reference oils.
How to Choose the Right Gear Oil
Refer to your OEM handbook for the API classification and the SAE viscosity grade. Everything else follows from those two numbers.
Step 1: Identify the required API GL rating
Determine whether your system calls for GL-4 or GL-5. GL-4 is specified for most synchronized manual gearboxes and transaxles. GL-5 is the standard for hypoid axles. If your manual specifies a manufacturer-approved fluid by name or part number, such as Ford 134 for certain tractors, that takes precedence over a generic GL rating.
Step 2: Select the correct SAE viscosity grade
Match the grade to your operating temperature range. Most vehicle applications call for a multigrade such as 75W-90 or 80W-140. Just as you would compare different SAE viscosity grades for an engine, you must ensure your gear oil thickness matches the climate and load expectations of your drivetrain.
Step 3: Verify the label
Confirm the product explicitly claims to meet your required specification. Look for the API service symbol, which shows the performance classification and SAE grade.
If a licensed product is unavailable, look for wording such as “meets or exceeds API GL-5” on the packaging. For agricultural equipment, check whether your manual permits STOU or UTTO fluids.
Step 4: Cross-check the data sheet
If you are uncertain, compare the product’s kinematic viscosity at 100°C against your manual’s requirements. This confirms the oil behaves as specified at operating temperature, not just at the grades printed on the label.
Closing Notes
Selecting the correct API classification is only the first step in maintaining your drivetrain. Keep in mind that gear oils are highly susceptible to moisture contamination. Even small amounts of water can react with sulfur-phosphorus additives to form sulfuric acid, which aggressively attacks internal components regardless of their “yellow metal” status.
Always inspect your gear housing seals during every differential fluid change; a perfectly specified oil cannot protect a system compromised by environmental ingress, aeration, or oxidative thickening.
