How Synthetic Gear Oils Protect Your Vehicle

A car or truck's engine isn't the only system that needs careful lubrication. The transmission and differential may be less obvious, but the demands they place on lubricants can be even greater. All the arguments for using synthetics in a crankcase apply doubly to synthetic gear oils.

Gear oil performs a fundamentally different job than engine oil. Unlike the sliding surfaces of cylinders and pistons, transmission or differential gears press hard against each other to transfer power. Since all the vehicle's power is transmitted through contact surfaces on just a few gear teeth at a time, the gears have to work under very high pressure. This is especially true of differential gears, which are at 90 degrees to each other and the contact surfaces even smaller.

This makes it critical that a steady lubricating film separates those load-bearing surfaces. If that film breaks down, the resulting metal on metal contact causes pitting and scoring, and debris starts to foul the gearbox. A gear oil thus has to do a delicate balancing act. Higher viscosity provides more protection and a more stable lubricating film, but it also means a thicker oil. As the gears push through that thicker oil, it absorbs some of their energy, resulting in lost power and reduced fuel economy.

Heat is another major concern for gear oils. "Thermal runaway" is an effect that happens when temperatures rise in the gearbox, causing a loss of viscosity in the gear oil. In turn, this causes more metal contact, more heat, and further loss of viscosity. As this vicious cycle continues, the gears eventually suffer catastrophic failure.

The very precise balance of viscosity and the need for high thermal stability means that synthetic gear oils have a significant advantage over conventional gear lubes. The absence of wax and other refining by-products makes synthetic gear oils considerably more stable at high temperatures.

Also, synthetics' precise formulations allow for very precise viscosities. This means there's a wide range of synthetic gear oils engineered for specific applications, from turbo-diesel and heavy pickups, to tow vehicles, all the way to off road vehicles and drag racing.

Compared to conventional gear oil, synthetics can do a better job of providing just the right viscosity to do the job and boost fuel economy. And they can better maintain that viscosity over the life of the oil to extend drain intervals and improve performance.