Synthetic vs. Mineral-Based Gear Oils: Which is Right for Your Vehicle?

Gear oil plays a crucial role in transmitting power to the wheels of a vehicle. It lubricates the gears in the transmission and differential, preventing metal-on-metal contact and wear.

Choosing the right gear oil can maximize the efficiency and prolong the life of your vehicle’s drivetrain. Two major types of gear oil are in common use today – synthetic and mineral-based.

But which one is right for your car, truck or SUV?

Here’s a breakdown of their key differences and how to select the ideal formulation.

What’s the Difference?

As the first thing, let’s take a look at the differences between these two oil options.

Mineral Gear Oils

Mineral oils are produced from crude oil and contain only refined petroleum-based compounds. Common types of mineral gear oils include 75W-90 and 80W-90 viscosity grades. Benefits of mineral gear oils include:

• Inexpensive – Mineral oils cost significantly less than synthetics, making them appealing for budget-conscious drivers. The raw material and refining costs are lower.
• Wide availability – Mineral oils can be purchased at most auto parts stores and service stations, even in remote areas. Supply is abundant.

However, mineral oils have downsides:

• Less stable viscosity – The thickness of mineral oils changes more with fluctuations in temperature compared to synthetics. This can impact lubrication.
• Shorter oil change intervals – Mineral gear oil breaks down more rapidly so it requires replacement more frequently – sometimes half as long as synthetics.
• Not as effective at extreme temperatures – Mineral oils tend to thin out too much at very high temperatures and freeze or gel up at very low temperatures. This reduces lubricity outside of moderate climates.

Synthetic Gear Oils

Synthetic gear oils are chemically engineered from select base oils and performance additives. Common types include 75W-90, 75W-140 and 80W-140 grades. The benefits of synthetic gear oils are:

• Outstanding cold flow properties – Synthetics maintain better viscosity at low temperatures for reliable lubrication in cold weather.
• Resistance to high heat – Synthetics are less prone to thinning, evaporating or oxidizing under high heat loading.
• Improved shear stability – Synthetics experience less viscosity loss when subjected to mechanical shear in the drivetrain.
• Long drain intervals – Most synthetics can safely go 50,000 to 100,000 miles between oil changes with used oil analysis.
• Cleaner operation – Synthetics keep internal components cleaner with less varnish, sludge or deposits over time.

The compromises with synthetics are mainly economic:

• Higher initial cost – Synthetics typically cost 3X to 6X more per quart than mineral oils. This expense is offset over years of use between fewer oil changes.
• Limited availability – Not all auto parts stores, quick lubes or rural gas stations keep synthetic gear oils in stock. Advance planning for purchases is wise.

When to Use Each Type

Here are some guidelines on when mineral oils and synthetics each make smart gear oil choices:

Mineral Oils Are Recommended For:

• Older vehicles with high mileage – Once wear is present, costly synthetics provide less benefit.
• Cars driven less than 10,000 miles per year – Long drain intervals of synthetics aren’t as necessary with little annual use.
• Standard transmissions and differentials without issues – Mineral oils suffice for routine lubrication in unmodified drivetrains.
• Towing within limits of the vehicle – For light or moderate duty towing below the vehicle’s capacity mineral oils remain adequate.

Synthetic Gear Oils Are Recommended For:

• New vehicles still under factory warranty – OEMs commonly call for synthetic gear oils to meet durability specifications.
• Performance, commercial or off-road vehicles – Synthetics withstand harsh conditions better.
• Frequent towing or hauling – The extreme loads synthetics can handle make them ideal for working vehicles.
• Operation in extreme climates – Synthetics flow better at very high or low ambient temperatures.
• Gearboxes with limited slip diffs – The frictional properties help prevent chatter and improve traction.

When to Upgrade from Mineral to Synthetic

Many drivers start using mineral-based gear oils in their vehicles when they are new due to the lower initial cost. However, at some point it may make sense to upgrade to synthetics if your driving usage changes.

Signs it’s time to switch to synthetic gear oil include:

• Increased Towing or Payload – Do you find yourself towing heavy trailers or hauling equipment more often? The extra stress on your drivetrain can be better handled by synthetics. They maintain viscosity despite higher loads and temperatures.
• Extreme Mileage on Factory Fill – If your vehicle has over 100,000 miles on its original gear oil, the additive packages are depleted. Replenishing with synthetic can extend useful oil life.
• Preventative Care for High-Mileage Vehicles – Proactively switching to synthetics at 75,000+ miles, even if not required, provides inexpensive “insurance” against wear as the mileage piles up.
• Climate Change – Are you moving from a temperate area to a climate extreme with cold winters or hot summers? Synthetics flow better at temperature extremes compared to more viscous mineral oils.
• Remanufactured Transmission – Did you rebuild or replace your transmission? Protect that investment by filling it with premium synthetic gear oil for its maiden voyage.
• Diagnosis of Problems – If you’ve had mechanical issues pointed to worn differential gears or bearings, synthetics can minimize further wear. Consult your mechanic.

Synthetic gear oils cost more upfront. But your vehicle’s transmission and differential are expensive components. The improved protection and extended drain intervals of synthetics can reward you with added years of reliable service from your investment.

Final Words

Make sure to consult your owner’s manual for the manufacturer’s specific gear oil requirement. But broadly speaking, synthetic gear oils offer performance advantages to exceed extremely demanding conditions. They are a smart choice if pursuing extended drain intervals to maximize convenience. Mineral oils remain suitable for average driving when following reasonable oil change frequencies. Consider your individual driving habits and requirements when deciding between these two gear oil technologies.