Red Line 50504 MT-85 75W85 GL-4 Gear Oil 1 Quart (4 Pack) - Quicker

In this review the Red Line 50504 MT-85 GL-4 gear oil is examined for drivers who want improved shifting and reliable gear protection in manual transmissions. The bottom line: this four-quart pack is best for owners of cars with brass synchros or applications that specify GL-1, GL-3, or GL-4 fluids, because it delivers balanced friction control and consistent performance even in cold climates. The reviewer found the fluid reduces notchy shifting, preserves synchro life, and offers peace of mind for popular applications such as Nissan 350Z/370Z and many Mitsubishi and Hyundai manuals.

Key Features

• High performance protection: Formulated to protect gears and extend synchro life, which helps reduce wear over time.
• Quicker shifts: Balanced friction control and slipperiness provide easier and more positive shifts, notably when temperatures drop below freezing.
• Safe for brass synchros: The GL-4 formulation lacks reactive sulfurs found in GL-5 oils, preventing damage to brass synchros.
• Broad compatibility: Recommended for GL-1, GL-3, and GL-4 applications and for many special synchromesh specs, making it suitable for a wide range of manuals.
• Popular OEM fitment: Commonly used in Nissan 350Z/370Z, many Maxima/Altima/Sentra models, Mitsubishi Evolution, and several Hyundai and Kia models.
• Trusted brand history: From a company established in 1979, positioned as a durable choice with no performance compromises.

Who It's For

This oil is ideal for owners of manual-transmission cars that require GL-4 or synchromesh-compatible fluids, especially where brass synchros are present and longevity of the transmission is a priority. Enthusiasts who drive performance cars like the Nissan 350Z, 370Z, or Mitsubishi Evolution will appreciate the improved shift feel and protection.

It is less suitable for drivers who need a GL-5 rated oil for hypoid gearsets where GL-5 is explicitly required, or for those seeking multi-vehicle convenience if a different specification is stated in some service manuals. Always cross-check the vehicle service specification before use.

Pros & Cons

Pros

• Excellent gear and synchro protection that helps reduce wear and extend part life.
• Improves shift accuracy and removes notchy shifting for many customers, including in cold weather.
• Formulated to be safe for brass synchros, avoiding the corrosive sulfurs found in GL-5 oils.
• Sold as a four-quart pack, convenient for full-service or multiple-top-up jobs.

Cons

• Not a GL-5 product, so it should not replace GL-5 where that specification is required by the manufacturer.
• Four-quart pack may be more than needed for a single small service depending on the transmission capacity.

Specifications

Product	50504 MT-85 Gear Oil
Viscosity	75W85
API/Spec	GL-4 (also recommended for GL-1 and GL-3)
Package Size	1 Quart bottles, 4 Pack
Compatible Vehicles	Nissan 350Z/370Z, many Maxima/Altima/Sentra, Mitsubishi Evolution, Hyundai, Kia, Quaife synchromesh
Safe for Synchros	Yes, safe for brass synchros
Brand Established	Red Line (since 1979)

Our Verdict

The Red Line 50504 MT-85 75W85 GL-4 gear oil is a sensible choice for manual-transmission owners who prioritize shift feel and synchro longevity. It offers clear advantages in colder climates and protects brass synchros where GL-5 could cause harm. For drivers of compatible Nissan, Mitsubishi, Hyundai, and Kia manuals, the four-quart pack represents good value and reliable performance when the vehicle specifies GL-4 or similar synchromesh fluids.

Frequently Asked Questions

Can this replace GL-5 oil?
No. This is a GL-4 formulation safe for brass synchros and should not be used where the manufacturer specifically requires GL-5.

Is it good in cold weather?
Yes. Customers report improved shift quality below 30F due to the balanced friction and slipperiness of the formulation.

How many quarts are included?
This listing is for four 1 quart bottles, suitable for multiple services or a full refill depending on your transmission capacity.