Lubrication Specifications

Componenttemperature rangeservice classificationS.A.E. Viscosity Specification
Engine and Carb Dashpots*Above 14°F (-10°C)API S.E.SAE 10 W/50; SAE 20 W/50;
SAE 10 W/40; SAE 20 W/40
-5°F to 50°F (-20°C to + 10°C)API S.E.SAE 10 W/30; SAE 10 W/40;
SAE 10 W/50
Below 14°F (-10°C)API S.E.SAE 5 W/20; SAE 5 W/30
Gearbox/ Overdrive**Above 30°F (0°C)
Below 30°F (0°C)
GL4 or GL1**
SAE 90 Hypoid oil
SAE 80 Hypoid oil
(or Castrol EP90 or EP75W90)
Final Drive
Above 30°F (0°C)
Below 30°F (0°C)
SAE 90 Hypoid oil
SAE 80 Hypoid oil
(or Castrol EP90)
TrunnionsallEP or SAE 90 Hypoid gear oil not grease!
Steering Rack Hubs & Chassis Grease PointsallNLGI 2 Multipurpose Grease
Brake and Clutch FluidallDOT 4
if in a bind: SAE Specification J.1703d and DOT3 (FMV SS116)
Anti-freezePermanent type ethylene glycol base with suitable inhibitor for mixed metal systems
Windshield WasherWindshield Washer Antifreeze Fluid (Proprietary Brands)

*Lighter oil can be used if car is running rich during acceleration. Our carbs are set up so that a thicker oil will resist the carb’s piston’s attempt to rise in the dashpot for just long enough that the engine’s increased load (when the throttle is opened) will pull more fuel across the bridge; this enriches the mixture and temporarily bumps power up to help the engine achieve higher speed more readily. A light oil will allow the piston to rise very fast allowing much more air… creating a lean mixture. 
Also, air tempature will effect the “thickness” of the oil. Colder = thicker. Engine oil (in the summer) is recommended for heavier damping. For light damping (in the winter), Marvel Mystery Oil is excellent or even 3 in 1 or sewing machine oil (remember, these thin oils will need to be topped up more as they leak out easier.)

Due to tuning, engine condition etc, the car many respond differently, so experiment… just don’t change anything else while you’re doing it. You can play with different oils on the same day, just blow it out or soak it up with a paper towel, so you can see the difference. If you see no difference with vastly different viscosity, something is wrong somewhere else.

**It is essential to use an EP (extreme pressure) oil to GL4 spec only for the diff and overdrive. DO NOT USE GL5. Virtually all oils now sold are to GL5 spec and will “melt” the copper washers in the diff. 80W90 GL1 is another great alternative. The GL1 can be found locally at Tractor Supply, farm stores or marine supply stores.
Mineral oils are usually EP90, semi synthetics etc can be EP75W90.
It is the sulphur and/or zinc based EP (extreme pressure) additives in the GL5 oil that can react with yellow metals above 200 deg. F and “melt” them. 

The gearbox isn’t so particular and any spec of EP oil can be used – as there is so little in there it is generally preferable to buy the most expensive as it will probably be the best.

Capacitiesnon-US marketUS market
Fuel37.6 liters9.9 gallons
Engine oil with filter change4.5 liters4.75 quarts
Engine oil without filter change4.0 liters4.25 quarts
Gearbox0.85 liters0.9 quarts
Gearbox with overdrive1.35 litres1.4 quarts
Final Drive0.57 liters.6 quarts
Cooling System4.5 liters4.75 quarts (1.2 gallons)

-1975 Spitfire Owners Manual and other sources

Carb Dashpot Level:
The dashpot should be filled to such a level that the damper (the knob on top of the carb) meets resistance when its threads are about 1/4″ above the dashpot. If in doubt, fill to the top.

Another method (for SU’s): To check the oil levels is to first remove your air filters. Raise each piston up into the bore with your finger. You should immediately feel resistance and it should start at the same point on each carb. If you feel any “free play” as you raise the piston (before the oil is raised in contact with the damper), then the level of oil in that carb is low.

Gearbox & Diff Oil Level:
Fill until oil drips out of the filler hole (up to the level of the filler hole).