Car Oil In A Dirt Bike: Can You Use It?

There are many things to consider when it comes to maintaining a dirt bike. Checking components for wear and washing your bike are both good habits that extend the life of the bike. But the kind of oil you use matters too, and many may wonder if they can use car oil in a dirt bike.

You can put car oil in a dirt bike, but it’s not advised. Dirt bikes use the same oil for the engine and the gearbox, so the oil must be specially formulated. Car oil doesn’t allow the optimal friction for the engine to transfer power to the drive train, and car oil additives can damage the bike.

Many people follow the adage that motor oil is motor oil. It’s just lubricant, right? But there are many things to consider when choosing the correct oil for your machine. In the article below, we’ll discuss the common factors that help determine which oil is right for your dirt bike.

Dirt Bike Oil vs Car Oil

Oil is a key factor for the optimal operation and long-term health of any engine. Motocross and dirt bikes are designed for use on natural terrain and face stresses on their components that are unique to their intended use. The lubrication system for dirt bikes works differently than the lubricating system for automobiles. Because of this, dirt bike oil and car oil are formulated differently.

Motorcycles utilize what is commonly called an “open system lubrication.” An open lubrication system means the oil circulates through the transmission and the engine itself and does not use separate, dedicated fluids for each component. Simply put, in an open system, one lubricant is used for all internal moving parts.

In motorcycles, not only does the oil serve to lubricate the engine and transmission, but it also lubricates the wet clutch system that ensures reliable, smooth, and steady gear shifting. The multipurpose-nature of motorcycle oil is designed to ensure dependable clutch performance.

What Does Motorcycle Oil Do?

Motorcycle oil serves to protect the engine and transmission by lubricating all moving parts, aiding in engine cooling, and keeping the inside of the engine clean. To achieve these goals, specific additives are used in motorcycle oil that differ from what is commonly found in car oil.

Often, detergents and dispersants are added to oils to keep debris in suspension and not allow it to stick to engine and transmission components. Solvents are added to break up any deposits that do form, and corrosion inhibitors and buffers are used to neutralize acids. All these additives help increase engine life.

In automobiles, the transmission is separated from the engine and the two mechanisms operate as close systems that require their own dedicated lubrication. Many of the same additives found in motorcycle oil are used in car oil, with one notable exception: Molybdenum. Any oil containing molybdenum should not be used in a motorcycle over the long term.

Why Not Molybdenum?

Molybdenum is added to car oil as an emergency lubricant in case of failure of the base oil. With a wet clutch system, this additive can lead to slippage and serious damage to the clutch system. Motorcycle oils rely mainly on zinc and phosphorous as emergency lubricants because they will not cause clutch slippage and failure.

Since most dirt bikes use gear movement to distribute oil within the crankcase, dirt bike oil is usually less viscous, or thinner, than conventional car oil and contains special anti-wear additives to reduce friction on both the engine and transmission.

Some of the additives and detergents in car oil are relatively high in ash content. These kinds of detergents can cause deposits to build up on the piston crowns and the valve train. When these deposits break loose, they could burn or perforate motorcycle engine components.

Motorcycle oils contain anti-foam agents, so using car oil in dirt bikes may cause the oil to become frothy inside the crank case. Since most motorcycles operate at much higher rpm than automobile engines and don’t have an oil vent large enough to equalize case pressure, using car oil can increase crankcase pressure to unsafe levels and eventually lead to catastrophic failure and cracking.

Can You Put Car Oil In A 4-Stroke Dirt Bike?

You can theoretically use car oil for engine lubrication in a 4-stroke dirt bike. However, car engines and motorcycle engines operate under different stress levels, and if the bike has a wet clutch system that’s not isolated, the friction-reducing additives in car oil can damage the clutch.

In 4-stroke dirt bikes, you should use a motorcycle transmission/gear oil in the transmission side and a 10w-40 motorcycle oil for the engine. During racing, temperatures in a 4-stroke dirt bike engine can reach as high as 265 Fahrenheit. Using a motorcycle oil instead of conventional car oils will help keep sludge, lacquer, and other deposits from building up on the engine components.

Can You Put Car Oil In A 2-Stroke Dirt Bike?

You can put car oil in a 2-stroke dirt bike, but it’s best to use dedicated motorcycle oil. While using car oil in a 2-stroke engine is not optimal, it’s not necessarily going to ruin your dirt bike. The key is not to use car oil consistently in a 2-stroke dirt bike.

One of the main reasons for this is the fact that in 2-stroke engines, the engine and the transmission are essentially connected to each other. As discussed earlier, this means that whatever is lubricating your engine is also lubricating your transmission. Motorcycle oil contains more high friction additives and has higher lubricating properties than car oil.

Using car oil in your motorcycle can ultimately lead to a lack of sufficient lubrication. This can lead to premature wear on your transmission gears and components and could eventually lead to metal shavings being sheared from the transmission and captured in the oil.

Since the transmission and the engine are connected in an open system, these fine pieces of metal can be carried to the engine and cause serious damage. In fact, some mechanics maintain that if the transmission in a motorcycle fails, it’s just a matter of time before the engine follows suit. In this worst-case scenario, the only option is to replace the entire unit.

What Are The Options For Motorcycle Oil?

In general, there are three main options for motorcycle oil: mineral, semi-synthetic, and fully synthetic. Mineral oil is the most basic option and can cost about a quarter of what fully synthetic oils do. Mineral oil has other advantages over the synthetic options as well.

Many motorcycles come from the factory with mineral oil in them since the oil aids in proper bedding of rings and pistons during the initial run-in stage. Using synthetic oils initially can cause a film around the bore and cause improper sealing, which could lead to slippage and higher oil use. Older motorcycles may benefit from using mineral oil because it’s thicker and less likely to leak.

In With The New

Semi-synthetic oil is a mineral oil blend that contains 30% or less synthetic oil in its formulation. These blends were developed as a compromise between mineral oils and fully synthetic oils and are intended to offer some of the benefits of synthetic oil while holding down cost. But by being largely mineral oil, these oils do not offer all the advantages of fully synthetic blends.

Fully synthetic oil is produced by processing and refining man-made chemicals. Since it’s not produced through crude oil refinement, fully synthetic oils can be formulated to offer superior resistance to high temperature and oil breakdown. Fully synthetic oils last longer and perform better than petroleum-based oils simply because they were designed to do so.

Final Thoughts

Using car oil in your dirt bike can negatively affect performance over the long haul and may eventually lead to engine failure and costly repairs. Following the manufacturer’s specifications as written in the owner’s manual is the best way to keep your dirt bike running at peak performance levels.