ULTRA 1PLUS SAE 75W-90 Synthetic Gear Oil GL-4 - Durable Protection

In this review of ULTRA 1PLUS SAE 75W-90 Synthetic Gear Oil GL-4, the bottom line is simple: this 5 gallon pail is aimed at professional mechanics, fleet owners, and enthusiasts who need a robust, year-round gear lubricant that reduces wear under heavy loads. The single biggest reason to buy is its advanced synthetic base and anti-scuffing chemistry that form a stable lubrication film, which customers say improves shift quality and quiets noisy gearboxes in transfer cases and transmissions.

Key Features

• Advanced GL-4 formula: Premium synthetic base oils provide superior thermal stability and cleanliness to help components run cooler and resist breakdown.
• Anti-scuffing protection: Special friction modifiers and anti-scuffing agents guard gears under extreme pressure to minimize pitting and surface wear.
• Year-round viscosity: Meets SAE J306 requirements for all-weather performance so it remains stable across a wide temperature range.
• Extended component life: Forms a robust lubrication film that reduces wear on gears and bearings, helping to extend service intervals and lower maintenance costs.
• Leakage resistance and cleanliness: Formulation reduces leaks and contamination risk while minimizing deposits for a cleaner differential or transmission.
• Limited slip additive package: Includes limited slip differential additives for consistent performance in limited slip setups.

Who It's For

The ULTRA 1PLUS 75W-90 GL-4 is best suited to technicians, fleet managers, and vehicle owners who work on automotive axle gears, manual transmissions, transfer cases, and limited slip differentials where GL-4 performance and synthetic stability matter. It is especially useful for high-mileage FWD gearboxes and heavy-use applications where quieter shifting and reduced wear are priorities.

Drivers looking for a budget consumer motor oil replacement for engine use should look elsewhere, and those requiring GL-5 specifications or specific OEM-branded fluids must verify compatibility before switching. This product is primarily formulated for GL-4 applications rather than extreme-pressure GL-5 use.

Pros & Cons

Pros

• Delivers smoother, quieter shifts in transmissions and transfer cases according to customers.
• Premium synthetic base oils improve thermal stability and reduce deposit formation for longer component life.
• Formulated to meet SAE J306 and exceed API GL-4 standards for dependable year-round viscosity.
• Includes limited slip additives for improved differential performance where required.

Cons

• Some customers noted mixed opinions on slipperiness and color, indicating subjective differences in feel and appearance.
• Not intended for applications that require API GL-5 chemistry without verifying compatibility.

Specifications

Product name	ULTRA 1PLUS SAE 75W-90 Synthetic Gear Oil, API GL-4
Container size	5 Gallon Pail
Viscosity grade	SAE 75W-90
API rating	Exceeds API GL-4
Meets	SAE J306 viscosity requirements
Key additives	Anti-scuffing, friction modifiers, limited slip package
Primary benefits	Thermal stability, reduced wear, leakage prevention

Our Verdict

ULTRA 1PLUS 75W-90 GL-4 in a 5 gallon pail is a practical choice for professionals and serious DIYers who need reliable, year-round gear protection and quieter shifting. Its synthetic base and anti-scuffing additives deliver long-term value by extending gear and bearing life, though users must confirm GL-4 compatibility for their specific application.

Frequently Asked Questions

Can this be used in limited slip differentials?
Yes. The product includes a limited slip differential additive package intended to support limited slip performance.

Is this suitable for cold-weather startup?
Yes. It meets SAE J306 viscosity requirements for year-round use and maintains adequate lubrication in low temperatures.

Will it work in transmissions that previously used GL-5?
Not necessarily; users should verify OEM recommendations and compatibility since this formulation is targeted to API GL-4 applications.