Gearbox oil: Which grade to use?

There is always some doubt in what type of oil should be used in a 500, 126 and a126 BIS gearbox.

If you are not sure what gearbox you have a simple rule of thumb is, if the gearbox has synchromesh then it’s from a 126 (or 126 BIS) and if it’s a ‘crash box’ then it’s a 500!

Model Fiat recommend Equivalent
500 all models TUTELA W 90/M SAE 90 EP
126 all models inc. BIS TUTELA ZC 90 SAE 90

means extreme pressure and refers to the additive in the oil. The additive is to stop metal-to-metal contact between the gears and is based on Sulphur/Phosphorous which forms a sacrificial chemical layer, thus protecting the metal. The sulphur gives EP gear oils their characteristic smell.

IMPORTANT NOTE: 126 gearboxes do NOT use EP oils, as the additives can cause erosion of some of the non-ferrous metals in the gearbox.