Differential Oil Change

75W-90 weight gear oil is recommended for the differential, changed at 30,000 mile intervals. First, make sure you can loosen the oil filler plug (23 mm) and you have a proper hand operated pump for pumping gear oil. Then drain the oil by removing the lower plug (24 mm) and remove any metal contaminants bound to the magnetic insert on the drain plug.

Add a new washer (same size as the oil drain plug washer) and plug, then replace the oil through the filler plug. Aluminum crush washers are used on the engine oil, transmission, and differential oil drain plugs. All crush washers are the same size (part number 9956-41-800). Oil should be added to the level of the filler hole. Filling can be accomplished under the car using a hand pump.

Torque Specifications

Differential drain plug: 39-54 N/m, 4.0-5.5 kg/m, 29-40 lb/ft
Differential fill plug: 39-54 N/m, 4.0-5.5 kg/m, 29-49 lb/ft

Changing the Rear Differential vent

Detailed instruction is found on Miata Net.

Spark Plugs and Plug Wires Installation

The NGK Premium RX plugs and NGK Power Cables were installed.

The new NGK Premium RX plugs are next-generation spark plugs with a maximized total performance. The plugs use ruthenium containing central electrode. According to NGK, the Premium RX plugs generate higher power, consume less fuel and last longer than iridium plugs.

Old and New Plugs

The Power Cables are the high performance version of the NGK spark plug wires. They have an extremely low resistance of 0.9 KΩ per meter. According to NGK, the Power Cables sustain a minimum level of spark energy loss and provide excellent starting and acceleration performance, idling stability, and fuel economy.

Torque Specifications

Spark plug: 25-30 N/m, 2.5-3.0 kg/m, 18-22 lb/ft

Loosen a Transmission Fill Plug

Miata uses a square-headed manual transmission fill plug.

It can be removed with a 14mm open end wrench, crowsfoot wrench or adjustable wrench.

If the plug is too tight, try a special tool, a 14 mm 8-point (octagon) socket. You can use a torque wrench with this.

Make sure you remove the fill plug before you remove the drain plug.

Torque Specifications

Transmission drain plug: 40-58 N/m, 4.0-6.0 kg/m, 29-43 lb/ft
Transmission fill plug: 25-39 N/m, 2.5-4.0 kg/m, 19-28 lb/ft