NA Fluids

Original Author: Phil Barnett (prb) - 2013

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(Please dispose or recycle all used fluids from your vehicle in a legal and proper manner.)

Engine Cooling System

Coolant capacity is 6.8 quarts when dry. Use Ethylene Glycol or a suitable newer replacement. The block is cast iron, the head is aluminum. Using 50-50 mixture for most of the US will cause borderline overheating to full overheating since too much Ethylene Glycol reduces cooling capability.

If you purchase full strength antifreeze to mix your own proportions, be sure to use distilled water for the mix down. Tap water contains ions which can cause your coolant to go bad quickly and can cause excessive corrosion and can even lead to water pump impeller failure.

Ethylene Glycol is sweet tasting and animals are drawn to it. Ethylene Glycol is poisonous to humans/pets/wild animals so if you drain your system, prepare a safe storage and disposal method. There are replacements for Ethylene Glycol which are non-toxic.

Ethylene Glycol Protection
Lowest TemperatureWater/Coolant Gravity at 20C {68F}
Above -16C { 3F }65/35 1.054
Above -25C { -15F }55/45 1.066
Above -40C { -40F }45/55 1.078

Mazda part number for the water pump gasket is B6BF-15-116.
The water pump inlet is B366-15-165.

These are far superior to paper gaskets. I can't recommend them enough.

Engine Oil

Engine oils suggested in the miata.net community are all over the map. The Miata community generally recommends any high quality synthetic oil. I recommend an extended size oil filter. I personally use Mobil 1 10W-30 in all of my vehicles. I'm in Florida and the temperature ranges you experience and driving you do may bear on which oil you use. These days, there are lots of great full synthetic choices. Choice of the weight and brand you use may be dictated by the HLA tick in your engine.

Between the high mark and the low mark on the dipstick (the checkered area) is .85 quart.

Engine Oil CapacityQuarts
Dry Engine 4.2
Oil Only 3.8
Oil and Filter 4.0

The NA 1.8 oil dipstick is 18" from flange to tip, 16 13/16" from flange to full mark.

Power Steering Fluid

The power steering system uses Dexron II or M-III. Capacity is .85 quart.

Manual Transmission Oil

Do not put non friction modified GL-5 grade gearbox oil in a Miata manual transmission. It's too slick and will make shifting difficult to impossible. Always use GL-4 grade oil for the manual transmission.

These transmissions respond very nicely to the relatively expensive Ford Motorcraft MTF synthetic transmission oil with friction additives (FMFSMTF or XT-M5-QS). The ford MTF synthetic was developed for the difficult to shift Mustang gearboxes and contains special friction modifiers that allow synchromesh to work better than standard GL-4 fluid. This fluid is a lifetime replacement so it's cost is defrayed over time and the excellent shifting it provides.

Fluid capacity is 2.1 quarts.

Weights recommended are 75W-90 for all season and 80W-90 for higher temperatures. I don't think you'll have a choice on this for the Ford MTF.

Always ALWAYS remove the fill plug before you drain the transmission. The fill plug is a tapered pipe thread and has been known to seize in it's threads. If you drain first and can't get the fill plug out, you are stuck without oil in the transmission. A bad place to be.

The fill plug is a square headed plug. Avoid the temptation to put an adjustable wrench on it because that can strip the head to a point where you will never get it out. An 8 Point 9/16" socket fits perfectly. Sears part number 50741. A stuck plug is more common than you think. Many people have cursed this plug after rounding it off with an adjustable wrench.

Some anti-seize when you replace the fill plug will prevent issues with removal in the future.

Manual Shift Turret

Under your center console there are two rubber accordion boots that allow the shift lever to move but keep dirt, hot air and smells from getting into the cabin and into the turret. You'll need to remove the shift knob, the center console, the upper boot and lower boot to get to where the shift turret is located and lubricated.

Use a turkey baster to remove as much fluid as possible and replace it with the same fluid you put into the transmission. If you don't feel like buying 3 quarts of the expensive Ford MTF, you can put any GL-4 fluid in there. There is a remote possibility that the shifter turret can leak down into the transmission body. If you open it up and find it empty, it would be a good idea to use identical fluids so if/when they mix you will have consistent lubrication in the transmission.

Replacement of any shredded/torn/deteriorated rubber accordion boots is indicated. R-Speed is advertising improved ones on eBay. Time will tell if they last longer but it's unlikely they will be worse than the factory boots which seldom make it through two years of daily driving.

Automatic Transmission Fluid

Miata automatic transmissions use Dexron II or M-III fluid. Total capacity is 7.7 quarts. Pan capacity is 4.2 quarts.

Differential Fluid

Miata differentials use GL-5 and require nothing special in that regard. Any good synthetic GL-5 will last 100k miles. Differential capacity is 1.06 quart. Above 0F use 90W, below 0F use 80W.

Drain/Fill Plug Gaskets

1990-1997 Miata:

Oil Drain Plug
Differential Plugs
Transmission Drain Plug

1999 + Miata

Differential & Transmission Drain Plugs

ManufacturerPart No.
Dorman 095149
Mazda OEM ISH9956-41-800

Size; M18-M24 or M18

Inside Diameter: 0.720"/18.30mm
Outside Diameter.: 0.937"/23.80mm
Thickness: 0.054"/1.37mm
Aluminum (but Copper is OK)

Fuel Capacity

Years Gallons Imperial Liters
'90-'93 11.9 10 45
'94-'10 12.7 10.6 48