I noticed a slight increase in my car’s fuel consumption after its last servicing. The only additional item in the servicing was a differential oil change which the workshop recommended. Will this affect fuel consumption?

Changing differential lubricant is usually overlooked by most owners. It is an important component of the transmission and every motor vehicle, including most electric vehicles, have one or more differential.

A conventional car has a differential between the left and right driven wheels. In the case of a four-wheel drive, there could be three differentials – between the front wheels, between the rear wheels, and between the front and rear axles.

The differential makes it possible for the left and right driven wheels to traverse arcs of different radii as in a curve, without causing disruption to power transmission. Note that the outer wheel has a longer arc and hence needs to rotate faster.

Not unlike engine oils, there are different grades and specifications. At the design stage, the transmission engineer will select a lubricant for optimum performance and efficiency.

The use of an incorrect lubricant in the differential could result in higher fuel consumption. An incorrect grade could result in increased friction, or increased fluid drag inside the differential owing to an overly viscous oil.

In either instance, there would be an increase in transmission losses, leading to a small increase in fuel consumption.