When is it better to use a Synthetic oil instead of a Mineral oil on a gearbox?

In normal operating conditions, mineral oils perform very well, providing perfect lubrication at oil bath temperatures of up to 80°C in continuous operation. Synthetic oils can be used with machinery that operates at higher temperatures of up to 120°C or 130°C. However, in operating conditions that reach a maximum of around 80°C, a synthetic lubricant will oxidise less quickly than a mineral oil and will double or even triple the oil bath's service life.