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Passenger Car Motor Oils and Motorcycles: Dangerous When Mixed

Passenger Car Motor Oils and Motorcycles: Dangerous When Mixed


Written By: Castrol Motor Oils

When it comes to questions about motorcycle oils, this is the one consumers ask us the most frequently: “Can I use the same motor oil in my motorcycle as I use in my car?”  Seems reasonable right?  Both have engines that require lubrication and both passenger car and motorcycle oil share some common grades like 10W-40 and 20W-50.  So, what do we tell them?  Absolutely not.  Why you ask?   

The key point of difference can be summed up in two words “common sump,” (maybe I should have said “sumped up in two words?”)  Motorcycles typically have one, while passenger cars do not.  So what does this have to do with the fluid?  Simple.  A common sump indicates that the lubricant needed to protect vital components in a bike’s engine, gearbox and clutch are contained in one place.  Since the fluid is stored in one place, it would stand to reason that there is only one fluid.  On the other hand, a passenger car has multiple sumps and thus require multiple fluids (transmission fluid, gear oils, etc.) to protect the same vital components.  So, critical  components for motorcycles are lubricated with a single fluid, while passenger cars require multiple fluids to protect the same components.

Although motorcycle oils and passenger car motor oil are similar in their composition, the additive packages are balanced differently due to the type of performance and protection they must provide.  Since motorcycle oils are lubricating three different components with a single fluid, they require a highly engineered additive package to address the unique requirements of each component.  A typical passenger car oil only has to provide protection and performance for the engine of which fuel economy and emission system protection are the key priorities. As such, passenger car oils include friction modifying additives which reduce friction in specific areas of the engine such as the valve train and piston ring/cylinder.  The reduction in friction yields fuel economy improvement.  Also, passenger car oil contains lower levels of Phosphorus and Zinc.  Both of these ingredients must be controlled to adequately protect the vehicles emission system.

Since a motorcycle is inherently more fuel efficient than a passenger car and fuel economy is not as important to the consumer, motorcycle oils do not require the use of friction modifiers.  In fact, friction modifiers can affect wet clutch performance.  “Wet clutch” simply means that the motorcycle’s clutch is immersed in oil.  Should a clutch be immersed in an oil that includes friction modifiers (like a typical passenger car oil), these additives will be absorbed on the clutch plates and as a result, the clutch will start slipping.  This will cause a loss of power transfer to the back wheel, overheating as well as increased wear.  Motorcycle oils, which do not include friction modifiers, are specially formulated to provide the appropriate level of “grip” to the clutch plates, but still provide the protection needed to ensure proper functioning and years of reliable service to the consumer.  In short, friction modifiers are good for passenger car engines but bad for motorcycles.

The other key difference is the level of antiwear additives used in motorcycle oil versus passenger car oil.  Motorcycle oils typically require high levels of antiwear additives to provide a protective barrier, preventing metal to metal contact in the transmission gears due to the extremely high loads between the gear teeth.  Direct contact of the gear teeth can lead to scuffing or scoring of the gear teeth surfaces while vibrations typical of high revving engines promote fatigue induced damage like pitting.  Passenger car oils do not need to lubricate the transmission as there is a separate lubricant (automatic transmission fluid) charged with this task (back to the common sump concept).  So, a passenger car oil will not have a high enough level of antiwear additives to lubricate and protect a motorcycle’s gearbox.

In summary, passenger car oils include additives (friction modifiers) that are harmful to motorcycle engine components and don’t include sufficient levels of antiwear additives that your bike needs to function properly.  Formulating a motorcycle engine oil means finding the optimum balance between engine protection, clutch performance and gear protection due to a common sump. Conditions which are not considered when formulating passenger car engine oils.  So, when choosing an engine lubricant for your bike, select one that is specially formulated for motorcycles.  Your clutch and gearbox will thank you and the reward will be years of reliable service. Click here to learn more about Castrol Motorcycle Oil.



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26 Responses

  1. Motorcycles and cars have different component part. They may have a somewhat similar mechanism but the parts are more complicated witn the care because they are bigger and have more features thus, there is a difference in lubrication.

  2. "Absolutely not" is absolutely the wrong answer. It actually depends on the type of motorcycle. Brands like BMW and Moto Guzzi have a separate engine and transmission with a dry clutch. Lubricants with friction modifiers would be beneficial for these engines by reducing heat and wear on critical engine parts.

  3. "Absolutely not" is absolutely the wrong answer. It actually depends on the type of motorcycle. Brands like BMW and Moto Guzzi have a separate engine and transmission with a dry clutch. Lubricants with friction modifiers would be beneficial for these engines by reducing heat and wear on critical engine parts.

  4. "Absolutely not" is absolutely the wrong answer. It actually depends on the type of motorcycle. Brands like BMW and Moto Guzzi have a separate engine and transmission with a dry clutch. Lubricants with friction modifiers would be beneficial for these engines by reducing heat and wear on critical engine parts.

  5. Motorcycles that have engines and transmissions with clutches that share the same oil should use an oil without, or at least with fewer friction modifiers in order to eliminate excessive clutch slippage and wear on the plates.
    Motorcycles with dry clutches as in automobiles can use and would benefit from slipprier oils because the clutch plates are dry, not bathed in oil.
    If you have been using "automotive" oil in your bathed clutch and don't have excessive slipping, simply change to the propper oil and enjoy riding.

  6. I was also confused about the concept. Rather searching in web getting practical knowledge is better. You may visit any good service center to inquire details on it. It was me following the same. I had been to 2-3 repair centers to find the logic behind it and making conclusion. Thinking casually, it should not be done but a part of my mind says it reasonable. After getting through this blog, one can made idea about this concept. Thanks a lot for making the update. Using the same motor oil in motorcycle that used in cars is a bad idea.

  7. Don't assume I am confused about this issue, you can use whatever you want in your bike, as for me, I will keep using the slippery motor oil in my Bmw and Guzzi.

  8. Fundamentals of Choosing Motor Oil for Your Car – Choosing the most suitable engine oil for your auto is the perspective that ought not be ignored. This is on the grounds that not all the oil sorts fit one and the same vehicle and some of them might even influence the way the auto will work.

  9. Cutting edge motors are turning out to be ever harder on the oil that greases up them. As motors and oil sumps have become littler decreasing the volume of oil the motor holds, execution improving augmentations like turbo changing have gotten to be basic. Toss in government orders for always enhancing efficiency and contamination control, and you have continually expanding requests put on engine oil.

  10. Is it really dangerous to use the motor oils in car? I had never thought of such depth. It was always I was in misconception. Thanks a lot for making me clear on it. I was thinking of using the motor oil once for my car, luckily I got to know about it earlier. Thanks.

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  13. Today's modern engines stress engine oil like never before! Engines are smaller, lighter and produce more horsepower per cubic inch than ever before and yet hold less oil volume. Horsepower increasing additions such as turbo charging and super charging have become common place.

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  15. I’ve been using car oil and only car oil in my motorcycle for the past 5 years and didn't find a problem. There is no slipping clutches, never had a single issue. Should I change the oil?

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