If you’re new to motorcycle ownership or motorcycle maintenance, you may have a lot of questions about the right way to properly maintain your bike. Many people have some extra car oil laying around and may wonder if it can be used in their motorcycle.
Most common car oils shouldn’t be used in a motorcycle. Motorcycles tend to have different oiling requirements than cars, and the average oil made for cars has substances within it that aren’t good for motorcycle components.
There’s a bit more to it though, as you might imagine. It’s important to understand which oils will work properly in your motorcycle, and why it is that car oil isn’t a viable option. I’ll go through some of these issues in more depth below.
So, what is it exactly that makes oil for cars and oil for motorcycles different? Well, to understand why these oils have different characteristics, we must first understand how cars and motorcycles use oil differently in their engines.
The average car uses oil to lubricate and cool engine components. The oil will circulate around the crankcase, lubricating components and distributing heat away from them. It’s designed to reduce friction as much as possible between otherwise harder components, allowing an engine to run for much longer if working properly.
The average car also has quite a few other fluids with slightly different purposes. Coolant is used to cool pretty much solely and circulates at a rapid rate to keep the engine at the right operating temperature. It doesn’t really lubricate anything and it doesn’t really serve any other purpose other than cooling.
Transmission fluid in cars is separate from oil. It has a different viscosity and mass and is used solely for cooling and lubricating the transmission. Since the transmission is a different component from the engine and turns in different ways and at different speeds, it makes sense to have a different lubricant that’s optimized for transmission longevity.
These are the 3 standard fluids that every car drivetrain needs to run properly. There are more fluids in the engine bay, such as brake fluid or power steering fluid, but they aren’t really in the engine or transmission so they’re not as relevant to discuss here.
Motorcycles use oil somewhat differently to cars. If you’re interested in motorcycles at all you may be aware that they’re generally simpler than cars. The vast majority of motorcycles don’t have a lot of excess components beyond what is required for simple operation. This is often true for fluids as well.
The average motorcycle has one fluid – oil. Some motorcycles will have coolant as well, but many bikes don’t and are still air-cooled. So, for these bikes, oil is responsible for way more jobs than in a car. It must lubricate the engine, lubricate the transmission, and cool the whole thing as much as possible.
As you can imagine, given that oil has so many jobs within the engine of a motorcycle, having the right oil is really important for long-term reliability. The oil will also be used more heavily, as most motorcycles don’t have a very high oil capacity and the oil will also be subjected to consistently higher engine RPMs.
For most motorcycles, oil is also used in the clutch system. A car has a “dry clutch” system, where a friction disc is used on a metal plate and pressure causes it to engage and disengage. A motorcycle, however, has a “wet clutch” system, which is a series of many friction discs and metal rings immersed in the oil of the crankcase.
A wet clutch uses oil and needs the right oil to operate properly. If the oil has the wrong viscosity, these clutch plates may not engage or disengage properly. Dirty oil can also cause some issues, so it’s important to change it regularly.
Now we get into the specific crux of the issue. Most car oil is not really pure oil. It’s produced with detergents and friction modifiers. These additional compounds are very helpful for car engines. They help clean the engine and promote more lubrication among components.
In motorcycles however, these modified oils can have terrible results. Specifically for motorcycles with wet clutches (which is most of them), oils with friction modifiers can greatly reduce the life of the clutch if not immediately cause it to malfunction. This is the biggest reason to avoid putting car oil in a motorcycle.
You shouldn’t use car oil in a 2-stroke motorcycle. 2-stroke motorcycles are a little bit different to both cars and 4-stroke motorcycles. The engine is simpler, runs in a different way, and requires gasoline mixed with oil.
When a 2-stroke motor runs, a mixture of gas and oil is combusted within the cylinder. This oil combustion is what gives 2-strokes their signature smoky exhausts. This is a different use of oil than in a 4-stroke motorcycle, in which having oil in the cylinder indicates the engine is not working properly.
So, with this oily fuel that is combusted by 2-stroke engines, we can identify the issue with car oil. Again, this will come back to the different compounds that car oil contains. The detergents within the average car oil are not meant to be in a combustion chamber either, and using this oil in a 2-stroke engine can result in the buildup of detergent deposits in the combustion chamber.
These deposits can be detrimental to long-term engine reliability, so it’s worth it to buy the appropriate 2-stroke oil, and it’s usually not super expensive. Car oil can certainly work in a pinch, but shouldn’t be used for a longer period of time.
Most 2-stroke motorcycles will also have separate transmission and clutch oil, and for the reasons discussed earlier, most car oil is not really suitable for this either. Again, just using the right weight of motorcycle-specific oil will be worth it in the long run.
You should not use car oil in a 4-stroke motorcycle. Car oils contain detergents and friction modifiers that are designed to work within a car engine, but these compounds can have a negative impact on your motorcycle’s 4-stroke engine in the long run.
Most engines these days are 4-stroke engines. 2-stroke engines were more popular earlier in the history of motorcycles and are still used in a lot of dirt bikes. But most street motorcycles sold these days are 4-stroke. You’ll still see occasional 2-strokes on the road, but they’re usually older bikes.
When discussing the average motorcycle, the default is usually considered 4-stroke (as most motorcycles are) and 2-strokes are often in their own separate category. As mentioned earlier, using car oil in a 4-stroke (standard) motorcycle can cause a lot of issues.
The friction modifiers and detergents that most car oil comes with simply aren’t meant to live within a motorcycle engine. Car oil can work temporarily, but using it for any long period of time will decrease the functionality and reliability of your motorcycle engine components.
Good motorcycle oil can certainly be more expensive at times, especially if you use name-brand oil. This does not mean it isn’t worth it, though. A motorcycle engine is a precision machine, and using the right fluid for it ensures it will perform well for a longer time.
If you use car oil in a motorcycle for too long, the results can be very unfortunate. For short periods of time, it’s unlikely you’d destroy anything, but the detergents and friction modifiers that car oil usually contains can have damaging long-term results on your bike’s engine.
The clutch may start to slip and wear much faster. You may notice clutch issues right off the bat, but they may take some time to appear. This will probably depend on the specific bike and the overall condition of your clutch.
The oil will also probably become dirty faster. Motorcycle oils are specifically designed to deal with the demands of oiling a bike engine properly, while car oils are not. Car oils are usually meant to be used in engines with a larger oil capacity and bigger oil filters.
This means that the car oil you put in your bike may break down more quickly and become unable to keep all of your engine, transmission, and other crankcase components properly oiled, leading to more wear on all of them.
Another issue that car oil can cause is a malfunctioning starter clutch. If your bike has a kick starter, you won’t have this issue, but if it has an electric starter, as many bikes do these days, using car oil could lead to a slipping starter clutch.
Replacing a starter clutch is not a job you want to do on most bikes, on some bikes it literally requires splitting the engine in half. The starter clutch is yet another component that’s really only designed to work with motorcycle oil, and usually a specific weight of motorcycle oil too.
The oil you should use for your motorcycle depends on your specific bike. Not only should you be using motorcycle specific oil, but you should also use the right weight of oil for your bike. “Weight” is a term used to categorize the viscosity of different motor oils.
The weight of an oil is assigned by The Society of Automotive Engineers (commonly shortened to SAE). If you’ve worked with engines at all, SAE is probably an acronym you’ve heard before.
Most engine oils are multigrade oils, meaning they have weight ratings for when they’re cold and when they’re hot. As oil warms up, it becomes less viscous and flows much more easily. The weight readings are taken from a cold engine and from an engine running at 210 degrees Fahrenheit, the standard operating temperature for most motors.
For example, in the case of 5w30 oil, the oil would flow with 5 weight when cold and flow with 30 weight when hot. This may seem a little weird if you’ve never looked into it, but it’s a standard metric that pretty much every oil out there uses, so once you learn it, it isn’t too hard to compare different oil weights.
Most bike engines are designed to use a certain weight of oil. The easiest place to find this is in the owner’s manual of your motorcycle. If your bike didn’t come with one, looking online usually yields a manual or forum results of people who have had success with different weights of oil in your bike.
What The Manufacturer Recommends
When in doubt it’s usually the best choice to go with whatever the manufacturer of your bike recommends. Some motorcycles may even have this oil weight physically listed somewhere on the bike, so it may be worth looking for.
Using different oils will change how the bike feels. It will change how the engine runs, how the clutch grabs, and how the transmission shifts. If you’re pretty mechanically inclined, it may be worth your time to try some different oil weights. As long as they’re safe for your bike, it shouldn’t cause any harm to try a few different ones and see what you like.
Some bikes will have multiple oil weights that work for them, while others will just have one. Whatever the optimal oil weight is can also change based on the season or the ambient temperature. The ideal oil weight for someone living in a warm climate will probably be different from that for someone living in a cold climate.
Using car oil in your motorcycle is an okay solution if you’re really in a pinch, but if you have the choice, using motorcycle oil will promote longevity, reliability, and better performance in your bike’s engine. In the long run, car oil will damage your bike’s engine and affect its performance.