![]() This means the oil will get thicker or more resistant to flow at lower temperatures. Similarly, for lubricants, as the temperature drops, the viscosity increases. Its viscosity can change depending on the influencing factors.Īs seen with the example of the water above, when the temperature decreases, the water can turn to ice. If water is at its freezing point (0☌), it can turn to ice but remains liquid at room temperature (around 20-30☌). For instance, water can assume other states depending on the temperature. Similar to the molasses and water examples above, different factors can affect the viscosity of a liquid. It will flow much faster than molasses (straight 50) with the same straw! The lighter-weight oil would also transfer heat and flow much faster than the heavier-weight (more viscous) oil. However, if a lighter weight (or less viscous) engine oil was used (such as a 0w20 or 10w30), then this is like someone trying to drink water (0w20) with a smaller straw. This would be equivalent to the user using a smaller straw for drinking molasses. The clearances also got smaller, and the engine oil was now required to flow faster, control the transfer of heat and contaminants and keep the engine lubricated.Ī straight 50 oil could not pass through the smaller straw at the speed it should. As such, most of these engines used a 50-weight (or straight 50) oil.Īs the technology evolved, the size of the engines got smaller. These engines had larger clearances for the oil to flow throughout the engine. We can draw this analogy to car engines over the last 30-40 years. However, getting the same liquid to the person using the straw would take longer if a thinner straw were used. Pulling the liquid from the cup will be easy using a big straw. GL-5 is suitable for hypoid gear service under severe service and shock loads and not for use in a gearbox.You can also apply this to using a straw for drinking water from a glass.GL-4 is suitable for hypoid gear service when they are under severe service but are without shock loading.Therefore it is not recommended to use GL-5 in a gearbox unless the manufacturer allows this. This can be disastrous for the synchromesh rings of a gearbox. Sulphur/Phosphorus additives however have an unfavourable property: they can react aggressively towards bronze and copper. This additive has the purpose to prevent the occurrence of micro-welds on the gear flanks at the local high temperatures which prevail in EP circumstances (temperatures well in excess of 800℃!) GL-5 has roughly twice the amount of EP additives compared to GL-4, which is why it is often used in high-pressure circumstances such as in a front axle and rear axle differential. Sulphur/Phosphorus containing products are used as EP-additive. The main difference between GL-4 and GL-5 gear oils is the amount of EP additives. The viscosity has no relation with the API Gear Oil Classification and should be chosen based on the recommendations from the manufacturer based on the temperatures where you will drive. It is important to know that the SAE Motor Oil Viscosity Chart (J300) is different from the SAE Gear Oil Chart (J306). ![]() The higher the Extreme Pressure (EP), the higher the GL category is. They are mainly important for the transport sector in North America, Africa and Asia. These different classifications define a certain level of performance in driven axles and manual gearboxes. There are four different classifications for transmission/gear oil. Choosing the right classification is extremely important since they both have different properties and wrongful use could lead to serious damage to your vehicle. When you are choosing a transmission or gear oil you might be wondering what GL-4 and GL-5 mean and what the differences are between these two classifications.
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