API GL-04 vs. API GL-05
Gear oil is a very important component in most automotive and machinery transmissions as it keeps friction between parts to a minimum and reduces wear. The American Petroleum Institute, which is better known as the API, classifies different types of gear oil. The two most common types of gear oil used in automobiles are GL-04 and GL-05. The main difference between GL-04 and GL-05 oils is the condition for which they are intended. GL-04 is designed for light to heavy conditions, ranging from small cars to buses and tractors. In contrast, GL-05 oils are designed for severe conditions where GL-04 may not provide sufficient lubrication; Specifically, for hypoid gears.
GL-05 contains over 50% more wear additives than GL-04. Although this contributes to the performance of the oil, it can be problematic in some cases, as some types of GL-05 oils contain harsh chemicals that can be ingested through yellow metals such as brass or brass. Most gearboxes use yellow metals, so the use of GL-04 is highly recommended to prevent damage to components inside the gearbox. There are some GL-05 oils that don’t use these harsh chemicals and are safe to use in gearboxes, but you want to make sure this is the oil you have before you put it in.
Aside from the troublesome gearbox, GL-05 oils are recommended for most other applications. Its performance is readily apparent in the way hypoid gears benefit from it. Hypoid gears experience much higher pressure due to the sweeping motion involved in contact. The extreme pressure additives in GL-05 oils help hypoid bevel gears cope with much higher pressures.
The general rule of thumb is to use GL-04 oil in your gearbox and GL-05 in the rest. But to be sure, you should check your vehicle’s owner’s manual to see which oils are recommended to use.
GL-04 is designed for light to heavy conditions, while GL-05 is designed for severe conditions GL-05 contains more anti-scratch additives than GL-04 GL-05 can be corrosive to some types of metals, while GL-04 is not. GL-04 is recommended for synchronized gearboxes instead of GL-05 GL-05 is used for everything else apart from gearboxes. GL-05 is better for hypoid gears than GL-04.