Which oil weight is best for my MX-5?

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Choosing oil for your car is no mean feat. With a myriad of different weights, specifications, and brands to choose from, it can be a minefield. We’ve put this guide together to help you choose the correct oil for your MX-5, whether it’s an NA, NB, NC, or ND.

Most oils usually have two numbers separated by a W to indicate their grade. The W stands for Winter and relates to the first number, indicating its viscosity at lower temperatures. For example, a 5W oil will flow better than a 10W oil when cold.

The second number indicates how the oil flows at high temperatures. Mazda originally specified 5W-30 for the engine oil, which is a good match for temperate climates all year round. However, a thicker oil can be used if bearing clearances are larger or the engine is operating at extreme temperatures, such as on track.

Originally the Mazda MX-5 NA was specified with semi-synthetic oil. We choose to run fully synthetic as it performs better at higher operating temperatures, retaining its wear protection properties better than semi-synthetic, where its mineral oil components start breaking down and evaporating. Mazda switched to fully synthetic oils when the BP-ZE VVT engine was introduced in 2001.

Below we have hand-picked our favourite oils for the engine, transmission and differential for all model years of MX-5.

5W-30 engine oil

For road cars that are occasionally used on the track, we specify a 5W-30 fully synthetic oil for all models.

NA NB NC ND
Engine 3.7L 3.8L 4.6L 4.3L

Amsoil

Develops a strong fluid film that keeps metal surfaces separated while its robust anti-wear additives further reduce wear in metal-to-metal contact regions for maximum engine life.

Red Line

Excellent wear protection and friction reduction across a wide range of operating conditions. Superior high-temperature stability and oxidation resistance increases lubrication.

10W-40 engine oil

For cars that are used in competition, we recommend a 10W-40 fully synthetic oil for all models, except the ND

NA NB NC ND
Engine 3.7L 3.8L 4.6L Not recommended

Millers

CFS’s triple ester formulation works synergistically for optimised film strength and anti-wear protection.

Red Line

An excellent choice for high-performance engines that see street/strip or track activity with high oil temperatures. Features thicker oil film at operating temperature than 20W-50.

Amsoil

Resists viscosity loss due to shear and is formulated with a heavy treatment of zinc and other anti-wear additives for excellent protection of high-pressure components in engines.

75W-90 GL4 gearbox oil

All gearboxes use 75W-90 GL4 transmission oil for all models.

NA NB NC ND
Transmission 2L 2L 2L 2L

Millers

Fully synthetic oils protect the gear teeth at both low start-up and high running temperatures, especially for high-performance road and track day applications.

Red Line

For 1989-2005 cars using Red Line oils, we use a 50/50 mix of MT90 and Lightweight Shockproof for extra protection under high loads. 2006 on require two bottles of MT90.

Amsoil

Designed to excel in severe service conditions that exceed the limitations of conventional fluids, particularly in performance driving conditions with increased shock-loading.

75W-90 GL5 differential oil

All differentials use 75W-90 GL5 gear oil for all models.

NA NB NC ND
Differential 1L 1L 0.7L 0.6L

Millers

Designed for the lubrication of competition gearboxes and axles which require limited slip high-performance oils. Optimised film strength increases anti-wear protection.

Red Line

Contains the extreme pressure additives necessary for the ultimate protection of road cars and racing vehicles, as well as friction modifiers for proper limited-slip operation.

Amsoil

Specifically engineered for maximum performance in severe-duty applications, with blend of high-viscosity, shear-stable synthetic base oils and an extra treatment of high-performance additives.

Oil capacities

In case you missed them, here are the required capacities for each oil for all models.

NA NB NC ND
Engine 3.5L 3.5L 4.6L 4.3L
Transmission 2L 2L 2L 2L
Differential 1L 1L 0.7L 0.6L

Oil coolers

Even though all the oils we have recommended perform far above those available off the shelf, when things start to really heat up on the track, relying on the performance of the oil alone to keep things lubricated is simply not enough. To extend the life of your oil—and your engine—we strongly recommend fitting an oil cooler. Keeping temperatures down will prevent the oil from becoming too thin, helping to maintain oil pressure and reduce wear.

Updated 04/06/2021

 

 

One comment

  1. A basic but often asked question. Really good you’ve taken the time to specify and explain what and why.
    Cheers

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