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Gear oil: Why it's important for your car

close up of transmission gearbox


The gear systems in your car engage in a lot of metal-on-metal contact, causing heat and wear-and-tear. Gear oil helps protect these moving parts by reducing friction and transferring heat away from them. Periodically changing your car's gear oil is essential maintenance which extends the life of your car and helps you avoid costly repairs down the road.

What is gear oil used for?

Gear oil is a lubricant designed for use in transmissions, manual gearboxes, differentials, transaxles and transfer cases in your car or truck. Gear oil helps your transmission run smoothly. More importantly, it helps protect critical internal components in your car’s gear systems from wear and heat damage.

Inadequate lubrication can result in the scouring, corrosion, scuffing, and pitting of important drivetrain components. This deterioration can compromise your car's performance, and eventually lead to costly repairs. Gear oil and motor oil are not the same thing, and they are not interchangeable. Gear oil is specially formulated for use on gears. Motor oil… You guessed it – it’s for motors.

How do I know which gear oil to use?

Check your owner's manual. Gear system specifications can vary from automobile to automobile. Using the wrong gear oil may result in poor performance or even damage to internal components, so it's important to use only the gear oil recommended by your vehicle’s manufacturer.

The American Petroleum Institute grades gear oils on overall performance, and GL-4 and GL-5 graded gear oils are the most common on the market. The vast majority of cars require GL-4 gear oil. Heavy-duty or high-performance automobiles, like trucks and sports cars may require GL-5 gear oil.

What happens if you don’t change gear oil?

If you don't change your gear oil according to the manufacturer's suggested schedule, you risk severe damage to your car's transmission and other gear systems. This could mean having to replace parts and repair your transmission, at substantial cost.

Gear oil deteriorates over time. Manual transmissions and other gear systems function with a lot of metal-on-metal contact. Natural friction grinds these moving parts down, and tiny metal particles slowly accumulate in the gear oil. These factors eventually compromise gear oil's lubricating qualities, so if your gear oil is not drained and replaced periodically, it will shorten the life of your transmission.


two rows of gear with oil

How often should gear oil be changed?

Consult your owner's manual first, but if you drive your car under normal conditions, you should have your gear oil changed every 48,000 to 80,000km (30,000 to 50,000 miles) for an automatic transmission and 96,000 to 160,000km (60,000 to 100,000 miles) for a manual transmission. If you regularly subject your car to severe conditions, like towing or driving in mud, you may need to change your gear oil as often as every 24,000km (15,000 miles).

What are signs that gear oil should be changed?

Pay attention to how your transmission feels as you shift gears. Does it slip or thump? Strange burning smells or whining or grinding sounds are also signs you should change your gear oil. Look out for leaks, as they can indicate contaminated oil. If your gear oil is dark or gritty, it's ready for a change. Finally, an illuminated "check engine" light on your dashboard is always a sign that something under the hood requires your immediate attention.