Which Motor Oil Is the Right One for Motorcycles?

Four crucial questions for the choice of engine oil

1. Is it an engine with plain bearings or with rolling bearings?
2. Are the engine and transmission supplied with oil together or separately?
3. Does the engine already have an oil filter in the main stream that needs to be changed?
4. Is the engine unopened and is it to be operated as it is, or is it to be overhauled from the ground up, meticulously cleaning all oil-bearing parts?

Why special motorcycle oil?

When our Japanese motorcycles first came on the market, car and motorcycle drivers still helped themselves from the same shelf when buying oil. Many of the owner’s manuals at that time recommended SAE 10W30 type API-SE as the oil quality – an oil that also lubricated the engine of the Opel Rekord. Today we are confronted with a completely different situation. In motorcycle construction, the block engine prevailed among four-stroke engines. In contrast to the car, the motorcycle engine, transmission and clutch form a single unit with a common oil supply. Increasing engine power made wet clutches and motorcycle transmissions a sticking point and led to the development of high-performance lubricants to prevent clutch slippage and tooth decay.

The specifications of car and motorcycle oils differ fundamentally and finally drifted apart with the introduction of the JASO 4-T standard in 1999. Modern car oils are therefore the certain death of many motorcycle engines, and conversely, special motorcycle oils do not belong in car engines.

8 decision criteria for the right motorcycle oil

1. Mainstream-filtered plain-bearing engines without embedded old wear are best served with modern oils. Used engines should not be switched to oils of a significantly higher class. Caution is generally advised with super-light oils.
2. Plain-bearing engines without a replacement filter cartridge in the main stream must not be operated with oils that contain detergents (cleaning additives) and thus have dirt-carrying properties. Classic HD multigrade oils (heavy duty) are the right choice here.
3. Rolling bearing motors without an exchange filter cartridge in the main stream are still well served by detergent-free mineral monograde oils, because the polymers present in multigrade oils are not compatible with heavily loaded rolling bearings. If multigrade oils are to be used, then the lower value must not be less than SAE10W; in the warm season, you are on the safe side with an SAE 20W-40 or 20W-50.
4. High-quality synthetic oils by nature have a more robust lubricating film, a larger viscosity index, age less quickly than mineral oils and semi-synthetic oils, and also offer greater safety in old engines, provided their specifications and additives permit their use. The latter can attack bearing materials and seals in very early years of manufacture.
5. Engines with a common oil supply for engine, transmission and wet clutch require special oils according to JASO MA or JASO MB with increased clutch friction coefficient and HTHS viscosity higher than 3.5 mPa*s (motorcycle oils).
6. Super-low-viscosity oils with their reduced HTHS viscosity do not belong in rolling bearing engines or in power units with a common oil supply to the engine and transmission and may generally only be run if there is express approval from the vehicle manufacturer so as not to risk engine damage.
7. Synthetic multigrade oils may cover a wider viscosity range than originally approved by the vehicle manufacturer, e.g. 10W-50 instead of 20W-40.
8. Gearboxes in two-stroke youngtimers run too cold for four-stroke oils and are better served with special oils (Motul Two Stroke Gear Box Oil 10W-30, also in full synthetic).

Engine oil for modern motorcycles

If the engine is the heart of the motorcycle, then the engine oil is its blood. But not all engine oil is the same. With the progressive development of motorcycle engines, the demands on the oil have also increased. Nowadays, it must be able to do much more than just lubricate and cool: It must still function at high temperatures and pressures and must clean the engine of combustion residues, abrasion, acids and fuel particles. Modern engine oils are high-tech fluids specially developed for specific motorcycle models.

Modern engines are robust, but they also need high-quality engine oils

A great deal has happened in engine and material development over the past 50 years. Whereas in the last century certain manufacturing tolerances were standard and wear-resistant coatings made of molybdenum or hard chrome were the exception rather than the rule, the picture has been reversed for some years now.

In today’s high-volume engines with corresponding manufacturer know-how, the engine quality is extremely mature. For example, today’s pistons have become significantly smaller and often have a graphite layer on the skirt. Piston rings in modern engines are much more elastic than in the past and operate with much less preload than in the past. Cams and tappets have long had wear-resistant surface coatings, and the valve seats in modern engines are designed to be extremely robust.

Nonetheless, even modern motorcycles can experience abrasion of high-strength steel from the crankshaft or connecting rods during the first few kilometers. But also residues of casting sand (so-called silicon carbide) from the engine production can initially remain with new engines. The first oil change is therefore extremely important, even on a modern motorcycle, and the machine should not be subjected to too much stress until then. In addition, one sometimes reads about poor quality of the first fill oil by the manufacturers.

Synthetic engine oils are ideal for modern motorcycles

Synthetic engine oils are inherently multigrade and use fewer additives than mineral oils. The additives that are mixed in are much more effective. That’s why synthetic oils perform much better than mineral oils (wider temperature range, lower oil consumption, lower friction).

• High-quality, fully synthetic engine oils naturally have a more robust lubricating film, a larger viscosity index and age less quickly than mineral oils and semi-synthetic oils.
• Power units with a common oil supply to the engine, transmission and wet clutch require special oils according to JASO MA or JASO MB with increased clutch friction coefficient and HTHS viscosity higher than 3.5 mPa*s (motorcycle oils).
• Super-low-viscosity oils with their reduced HTHS viscosity may generally only be run if there is express approval from the vehicle manufacturer, in order not to risk engine damage.
• Synthetic multigrade oils may cover a wider viscosity range than originally approved by the vehicle manufacturer, for example 10W-50 instead of 20W-40.

Last but not least: Fresh oil lubricates best. Oil ages not only during operation, but also through the effects of time. With oil change intervals cut in half, you spoil your engine. When you start it, it must also be completely warmed up, at least 25 kilometers. Every cold start means wear, because the oiling time can take minutes. Just starting it briefly and then putting it away for weeks or months is poison for any engine. We reveal everything else you need to know in the big engine oil advisor.

Car oil: dry and wet clutch

In automotive oils, additives are mixed into the engine oil; these additives minimize the friction of the components. Silicones, for example, minimize friction in cars, but are unsuitable for motorcycles because the clutch here runs in an oil bath. The reduction in friction would deprive the motorcycle of shear stability.

There are also differences from motorcycle to motorcycle. While 2-strokes mix gasoline and oil and require less viscous oil, 4-strokes have separate circuits for oil and gasoline. In the latter, the lubricity of the oil must be guaranteed in the long term.

Here, too, you must resort to the appropriate oil, otherwise you will jeopardize the lubricity of the oil and the functionality of your exhaust.
Whether motorcycle or automobile, you can quickly find out which oils are approved for your vehicle in the owner’s manual (or on the Internet, of course). In addition to the ISO, API and SAE standards, the JASO (Japanese Automotive Standard Organization) specifications also apply to Asian motorcycles. The oils are not only matched to the models, but also to the operating conditions.

Can engine oil for the car also be used for a motorcycle?

The answer to this question is a clear no. The operating conditions in a motorcycle engine are different from those in a passenger car engine. The engine speeds and thus the piston speeds are much higher. The engine temperature is also higher. The engine oil in the oil sump of a motorcycle can reach temperatures of up to 160 degrees. In some motorcycles, the motorcycle oil also lubricates the transmission and clutch. Motorcycle oil therefore contains other high-performance additives and has a lower ash content. The ash content of passenger car engine oils is partly responsible for deposits on the exhaust valves and, in a motorcycle engine, can lead to burns on the piston rings or cracks in the piston.

What is the difference between mineral oil and partially or fully synthetic motorcycle oils?

Mineral-based motorcycle oils are obtained from petroleum and are the simplest motorcycle oils. By adding various additives, the properties of mineral oils can be adapted to the requirements of a motorcycle engine. This means that even the inexpensive mineral oils such as MOTUL 3000 4T 10W40 do their job very well and are recommended for older motorcycles. Modern high-performance motorcycle oils can attack the seals of older engines if necessary.

Semi-synthetic and fully synthetic motorcycle oil

Semi-synthetic motorcycle oils are a combination of mineral and fully synthetic oils. The basis is a mineral oil, to which a certain proportion of fully synthetic oils is added, depending on the intended use. The admixture can improve the lubricating properties, shear strength and temperature resistance of the base oil. The advantage of semi-synthetic oils such as CASTROL POWER1 10W40 4T is the lower price compared to fully synthetic motorcycle oils.