ATV/UTV Transmission & Differential Oil Change Tips

Ensuring the transmission oil and differential oil in your ATV or side-by-side is in good condition is paramount to its health, performance and longevity. 

Fresh gear oils lubricate, cool, prevent corrosion, and reduce wear and internal stresses. The transmission oil and differential oil are two of the most vital fluids in your ATV or UTV. And just like any other fluid in a vehicle, these oils have a shelf life and need to be replaced periodically. In fact, gear oils on your ATV or UTV should be checked and replaced regularly as part of your routine maintenance schedule, and sometimes even more often.

ATV and UTV Transmissions vs Differentials

An ATV's or UTV's transmission is essentially the gearbox, while the differential is often referred to as the gear case.

On many ATV/UTV makes and models, the transmission is incorporated within the engine housing as opposed to being a separate unit. In most cases, when a transmission is housed within the engine, it uses the same oil as the engine itself. For those ATVs and UTVs that have transmissions separate from the engine, a different type of oil is required.

Depending on whether it's a 2WD or 4WD, and chain driven or shaft driven, an ATV or side-by-side might have one, two, or no differentials at all. For example, the Polaris Sportsman 850 has a front differential, a transmission and a rear differential, each of which requires a different type of oil. On the other hand, the Honda TRX 400 has a transmission and no differentials, and its transmission uses engine oil. The differential is a unit that takes power from a central driveshaft and sends it to the wheels via half shafts. Differentials use a thick, viscous type of specially formulated oil.

When to Check Transmission Oil & Differential Oil

Transmission Oil. You should check the level of your engine oil and transmission oil before every ride. Unless your ATV/UTV's transmission shares its oil with the engine, you'll have to remember to check both oil levels separately.

Differential Oil. Most ATV and side-by-side manufacturers recommend the differential oil level is checked at least once a year, or every 1000 miles. However, submerging your vehicle in water or deep mud is a surefire way to ruin your ATV or UTV, so you should check the diff oil if you do submerge it to ensure no contaminants have penetrated the differential. After all, the cost of replacing contaminated differential oil is a lot cheaper than having to replace a differential assembly that became worn because the oil wasn't regularly replaced.

Signs Transmission Oil & Differential Oil Need Replacing

Transmission Oil. Usually when there's an issue with the transmission, riders immediately fear the problem is with the transmission's internal gears and other mechanical parts. However, quite often the cause is the transmission oil, or lack thereof. A low level of transmission oil leads to excessive noise from the transmission. When the transmission oil becomes seriously depleted, you'll experience clunky or grinding gearshifts, or even gear slippage, which feels similar to the chain skipping a tooth on the sprockets.

The next time you feel your transmission isn't as smooth as it should be, or that your chain has slipped on a sprocket, check the transmission oil level before you panic. Changing the transmission oil and filling it to the correct level could well provide a quick and easy cure to your gear-related woes.

When inspecting transmission oil, check that it has a light color and that it's free from tiny metal particles, which are signs of mechanical wear. If the transmission oil is dark brown from age and use, or is blackened by tiny contaminant particles, it's time to replace the oil.

Differential Oil. A front or rear differential in need of fresh oil is usually marked by excessive noise from the diff. A lack of differential oil generally results in a whining sound, which eventually becomes more of a howling sound if the oil is not replaced.

Leaks. Signs of a leaking transmission housing or differential unit should be dealt with as soon as possible. There are numerous seals and gaskets in the transmission and diffs that wear over time. Typically, a leak will begin slowly and might only be recognized by excessive dirt sticking to oil around the area that is leaking. However, a leak will eventually become big enough that the surrounding area is coated with oil and will start dripping. A leaking seal or gasket needs to be replaced before the transmission oil or differential oil is replenished. 

How Often Should You Change ATV or UTV Gear Oils?

Your vehicle's owner's manual will tell you when the manufacturer recommends the transmission and differential oils need to be changed. However, the owner's manual only provides guidelines and doesn't account for riding in harsh conditions.

Riding in sand or mud puts a far higher strain on a transmission, so if you regularly ride in those types of conditions, use common sense and replace the transmission oil more often. The same applies for the differential oil. If you're regularly immersing your ATV or side-by-side in deep water or mud, you're increasing the chances that water or other contaminants will penetrate the differential and mix with its oil, which quickly wears the differential's internal parts.