Red Line MT-90 75W90 GL-4 Gear Oil – 946ml • 50304

Red Line MT-90 75W90 GL-4 Gear Oil • 50304

Replacement / service Red Line manual transmission lubricant for Mazda MX-5 NA, NB, NC and ND/RF manual gearbox applications listed in the compatibility table.

This full-synthetic, ester-based SAE 75W-90 lubricant is designed for synchronised manual transmissions and transaxles requiring API GL-4 performance. Its synchroniser friction characteristics are intended to support shift quality, and Red Line states that MT-90 is safe for brass synchronisers.

MT-90 is used in the manual gearbox only. One bottle contains 1 US quart, approximately 946 ml. The listed MX-5 gearboxes generally require approximately 1.8–2.1 litres depending on gearbox type, so three bottles are the practical order quantity for a complete service on most applications.

Common reasons for replacement include routine servicing, unknown or aged lubricant, contamination, leakage repairs and gearbox removal or overhaul. Fresh lubricant cannot correct worn synchronisers, bearings or other internal gearbox damage.

• Product type: Full-synthetic, ester-based manual transmission gear oil
• Primary use: Synchronised manual transmissions and transaxles
• Location / system: Manual gearbox
• Brand: Red Line Synthetic Oil
• Product reference / SKU: 50304
• Viscosity / grade: SAE 75W-90
• Specification: API GL-4
• Container size: 1 US quart / approximately 946 ml
• Synchroniser note: Formulated with synchroniser friction characteristics and stated by Red Line to be safe for brass synchronisers
• Application restriction: Not for automatic transmissions or differentials with hypoid gears

Fitment advice: Suitable for the listed manual gearboxes where API GL-4 SAE 75W-90 lubricant is required or permitted. For ND and RF models, Mazda Original Long Life Gear Oil IS is the preferred factory lubricant for optimum shift feel; Mazda permits API GL-4 SAE 75W-90 when the preferred lubricant is unavailable. For imported, modified or previously repaired cars, matching the required fluid specification, gearbox type or existing service data is recommended. Do not use MT-90 in an automatic transmission or as the lubricant for a hypoid rear differential.

Other items to consider: When changing this product, you may also want to consider purchasing new drain and fill plug sealing washers, replacement plugs where the existing fittings are damaged, a gearbox oil transfer pump, brake cleaner, protective gloves and absorbent materials.

Useful tools / consumables: A vehicle lift or suitable jack and axle stands, the correct socket or hex tool for the gearbox plugs, a torque wrench, drain pan, fluid transfer pump, eye protection, gloves and workshop cleaning materials.

Difficulty guide: DIY Difficulty: Moderate. Safe access beneath the vehicle, level positioning and the correct fill-level and plug-tightening procedure are required.

Why Red Line? Red Line Synthetic Oil is known for high-performance lubricants, fluids and additives developed for demanding road, track and motorsport use. Red Line products are chosen by enthusiasts and workshops for their focus on protection, thermal stability, shift quality, friction control and application-specific performance.

What’s in the bottle: One sealed 1 US quart / approximately 946 ml bottle of Red Line MT-90 75W90 GL-4 Gear Oil. A transfer pump and service hardware are not included.

Service notes: Loosen the gearbox fill plug before removing the drain plug. Keep the vehicle safely supported and level, drain the lubricant when safely warm, replace sealing washers where specified, fill to the correct service level and tighten the plugs to the model-specific torque. Red Line states that MT-90 is compatible with petroleum and other synthetic lubricants, although a complete drain and refill is preferred for a controlled service. Dispose of used lubricant responsibly.