Gear oil isn't necessarily something that the everyday motorist is in the know about and when you take a bottle of it off the shelf you are confronted with jargon which, unless you are up on the terms, will probably mean very little to you. So let's break it down term by term and make some sense of it all.Gear Oil TypeOne of the first things you should notice on a bottle of Granville Gear Oil is this piece of information explaining which type of gear train the oil is suitable for:Different gear designs have different rotation speeds, torque and so on which mean that gearboxes require specialist care depending on the configuration of gears.       Hypoid Gear Oil       Hypoid gears have high hydrodynamic pressure and so need a gear oil which can handle this       Limited Slip Differential Oil       Balances the torque between wheels to limit slip so they require gear oil with friction modifiers       Semi-Synthetic Gear Oil       A blend of synthetic & mineral oil which has greater resistance to shear breakdown.Viscosity IndexIf you know a bit about motor oil then you might notice some similarities here:Gear Oil tends to be multi-grade which means that it has been designed to behave differently at varying temperatures. In this instance, the number before the 'W' tells you how the oil behaves when cold and the number after the '/' denotes how it behaves when hot. However, this is where the similarities here end. You might think that, because the numbers denoting viscosity are so high compared with motor oil:Actually, the SAE rating of gear oil is different to that of motor oil. The 75W/80 pictured above is roughly similar to a 10W/30 motor oil in viscosity. This being said, a 10W/30 motor oil would not be a suitable substitute for the 75W/80 gear oil for reasons to be explained below.EP? EPEX?One of the main reasons that motor oil cannot be substituted for gear oil is the additive package. On Granville Gear Oil you will notice this:This gives you information regarding the additive package in the gear oil. EP and EPEX mean 'extreme pressure' which are designed to decrease wear to components which are exposed to high pressures. These are hardly ever found in motor oils but are essential for certain types of gearbox. LS in this instance denotes gear oil suitable for Limited Slip Differentials which require specific friction modifiers for optimal performance.API RatingGear Oils are classified by the American Petroleum Institute (API) using GL ratings. Firstly it should be noted that it is a common misconception that the GL rating reflects the viscosity of the gear oil.Currently GL-4, GL-5 and MT-1 are active to categorize gear oil.     GL-4     Denotes lubricants intended for axles with spiral beve gears operating under moderate to severe conditions of speed or            load, or axles with hypoid gears operating under moderate conditions of speed and load.     GL-5     Denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high              speed/shock load and low-speed high torque conditions.     MT-1     Denotes lubricants intended for non-synchronized manual transmissions used in buses and heavy duty trucks.Making The Right ChoiceThe most important thing to remember when considering a Gear Oil purchase is to check your owner's manual for the correct specifications for your vehicle. Whilst it might sometimes be tempting to use a substitute it is important to remember that the components of your gearbox require very specific additive packages in order to ensure that it operates at optimal performance. Using a Gear Oil other than that recommended in your handbook may cause long term damage to components and may void your warranty. --This article is intended for general information only and is not intended as a diagnostic tool. Always consult your user manual before attempting any maintenance on your vehicle."vV65197830VvArticle first published Wednesday 30th Mar 2016 10:00:00

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