We may earn commission from links on this page at no extra cost to you. We only recommend products we back!
The American Petroleum Institute (API) describes the properties of gear oils into specific categories like GL-4, GL-5, MT-1 etcetera. Among all, GL-4 is the most usable one as a lubricant. But can you use GL-5 gear oil instead of GL4? Will it be compatible with the engine that uses GL-4 before?
Can You Use GL-5 Gear Oil Instead Of GL-4?
Yes, you can use GL-5 gear oil instead of GL-4. But that does not mean you should. The most important fact here is the API GL rating.
You might be thinking the rating of GL-5 is higher. Then, why are you interrupted from doing it? We are going to discuss broadly so that you can understand why you should not do the replacement.
|Red Line 75W140 GL-5 Gear Oil||● Contains additional friction modifiers.|
● Offer excellent lubrication under extreme conditions.
● Provide additional slipperiness to lower operating temperatures.
|Sta-Lube API/GL-4 Multi-Purpose Gear Oil||● Highly Reliable.|
● Includes anti-corrosion additives.
● Anti-wear gear oils.
There are some reasons which will stop you from replacing the GL-4 with GL-5 gear oil. Here are some more details about the reasons.
The Additives Are Based On Sulphur and Phosphorus
The higher GL rating will provide higher EP protection. Therefore, it will need more additives. Mainly, the EP additives are made from Sulphur or Phosphorus compounds.
If you have any knowledge of chemistry, you will indeed be concerned to hear it. Let us tell you as we consider you do not know. The nature of these Sulphur or phosphorus-based compounds is to adhere to the metal surfaces. It is because they create a polar attraction with the metals.
They Attack the Metal Surfaces
When the EP additives are introduced to the metal surfaces, they attach through metal wetting polar attraction. Then the heat is produced, and the additives attack the metals. This attack is so aggressive that it wears out the synchronizers prematurely.
So Which One Has Fewer Additives But Standard Protection?
Typically, the GL-4 products use additives that have half of the Sulphur and phosphorus compound amount that GL-5 products use. It means you will have less EP protection. But your synchronizers will be out of the possibility of getting damaged severely.
When you use the GL-5 gear oil, you will get extra protection for the gears. Still, eventually, the synchronizers will get damaged.
The synchronizers might wear to the point where they cannot make contact with the other side of the cone and might bottom out before even stopping the opposing gear.
What Are The Difference between GL-4 and GL-5?
Both gear oils are of the same category. But what is the difference between GL-4 and GL-5? Let us show you the differences with detailed information.
Extreme Pressure (EP) protection is defined according to the GL ratings. The ratings are started with GL-1 to GL-6 and MT-1. When the GL rating is 5, it will give higher protection in extreme conditions like speed, loads, and torques.
But the GL-4 will provide you with less protection compared to GL-5. It will also handle less speed and torque. In high temperatures and pressure, the GL-5 is better. But that does not make it GL-4 too weak. It maintains legal protection to the gears.
The EP additives are one of the key differences here. They contain Sulphur and phosphorus compounds which are very corrosive. When the gear produces much heat, the Sulphur and phosphorus compounds attack the metals. Therefore, it would be best to have fewer additives.
The GL-4 gear oils contain less amount of these compounds. On the other hand, GL-5 oils have an incredible amount of Sulphur and phosphorus.
Lead is also used in those additives to reduce the wear in loaded gear sets. Though lead is not very environment friendly, its effects will be reduced when you combine them with Sulphur and phosphorus. The GL-4 uses less amount of lead compared to GL-5.
The viscosity of oil matters when you are using it on your gear. As we know, the GL-4 oils have less than a few Sulphur compounds, which helps to reduce the viscosity of the additives. On the other hand, the GL-5 oils have higher viscosity due to more excellent additives.
Reaction with Metal Alloys That Used Copper
The GL-5 oils are more active on metals surface when they are made of metal alloys. Sometimes copper is used as an alloying element. The result is disastrous when you add oils that have a more significant amount of Sulphur. In this category, the GL-4 oils are less reactive with copper.
The GL-4 gears oil is suitable when the gear is hypoid. They will give you standard service under severe conditions. But the oils are without shock loading. When it comes to GL-5 gear oils, they will also give you powerful service and shock loads. But most of the manufacturer does not recommend using it in your gearbox.
Can You Mix GL-4 And GL-5?
We would not answer negatively. Suppose you do not find any GL-4 gear oils directly or have a less amount of GL-4 oils. Hence, can you mix GL-4 and GL-5 to use in the gearbox? Well, a mixture of GL-5 and GL-4 can be used in the gearbox.
You can also use a mixture of MT-1 and GL-5 to put into the gearbox. But all the engineers recommend not to use the GL-5 in the engine. Even if you the mixture with GL-4, there will always be a possibility that it might damage the bronze parts in a gearbox.
Therefore, it would be best not to use GL-5 in the gearbox, not even the mixtures. This could be applicable only for emergencies when the GL-4 is not being found directly.
Which One Is Better?
The GL-4 gear oils are better when it comes to using the gears for a long time without replacement. From the discussion above, you must know about the additives used in these oils and the EP protections.
To get extra protection in extreme conditions, it will do a fool’s job to use GL-5 in the gearbox. That is because the Sulphur and phosphorus compound and lead additives will destroy the gear’s metal surface and metal alloys.
The GL-4 oils will not be this corrosive and will give you standard protection. Without a doubt, GL-4 gear oils are better than GL-5 oils. They are also the right choice if you are concern about the gear’s longevity.
Some Final Tips
If you are thinking about using GL-5 gear oil instead of GL-4, you have to know some tips. First of all, no one knows better than the manufacturers who made different types of these oils.
As they made different categories, it will not be wise to violate their categories and interchange the lubricants. Another thing to notice is to remember the properties of each lubricant that you are using in your engine. It should help you in these situations.
Don’t know actually what is GL-5 and GL-4? Here you go-
What Is A GL-5 Gear Oil?
GL-5 is a type of lubricant which is used in gear, especially hypoid gears. It is also used in axles operation under different combinations. Then what are those combinations?
Mainly, the combination is made from different speeds and torques conditions. For example, it could be high speed or shock load and low speed or high torques if you think about the combinations. The GL-5 gear oils protect the gears and affect the synchronizer so that there will be no trouble while you are riding.
The higher GL rating here means the extreme pressure (EP) will be of a higher level. Still, confused? Well, it means the gears will get higher protection in extreme pressure conditions.
Read our best gl-5 gear oil review to know more about it.
What Is A GL-4 Gear Oil?
The GL-4 gear oils are used in axles with spiral bevel gearings as a lubricant. These gear oils are famous for working under moderate to severe conditions. It could be speed and load or axles with hypoid gears.
Mainly, the gears operate at reasonable speed and loads. This is why most of the manufacturers select this type of gear oil. You can use them in specific manual transmission and transaxle applications. When the MT-1 lubricants are not suitable to use, surely you can use the GL-4 gear oils.
The GL rating is of this gear oil is lower than the GL-5. That means it will be able to give less protection than GL-5 in extreme pressure conditions.
Gear oils are the lubricants that help with the speed and loads. They are specified about their functional areas and their properties.
Hence, can you use GL-5 gear oil instead of GL-4? We will not recommend it. That is because you will quickly notice the result if you use the GL-5 oils. Take care of your car if you want to enjoy the ride without facing trouble.