GL4 Vs GL5 – Which Gear Oil to Buy for Your Car?

Finding the right gear oil for your automaton can be a hassle in many ways. While there are many choices that you can choose, not many can be counted to be as useful as GL4 and GL5 gear oils.

But what about gl4 vs. gl5? Well, the main difference is in the shock loads. Hypoid gear servicing without shock loading is possible with GL4, but when it comes to high-service hypoid gear with shock loads, the GL5 is your best bet.

Well, are you interested to know more about these oils for manual transmission? Well, you are in the right place to do so. All you need to do is scroll down below and keep reading. 


GL4 Vs GL5 – Parameters

SAE Grade80W-9075W-90
Specific Gravity0.8860.891
Typical Visual ColorL3.0L2.0
Flash Point478 F419 F
Pour Point-26 F-49 F
Viscosity Index 98152
LicenseAPI service GL4API service GL5

How Is API GL4 Different from API GL5?

Gear oil is a very important necessity that you must apply to your gear for the best performance of your car and vehicles. However, it is indeed a confusing matter to look at shoes between the GL4 vs GL5.

Below, we have compiled some of the major differences between the two that you can use to determine which among the two is the best choice between the API GL4 and API GL5 gear oil.


Viscosity is an important factor that you need to think about when determining the differences between two different oils with different numbers of carbons.

GL4 oil has lower amounts of sulfur particles than its counterpart which makes it slightly less viscous when compared to the GL5 gearbox oil.


We have already mentioned the sulfur particles being present in the GL4 and GL5. However, that is not the only EP additive that has been added to the oil.

Other than sulfur, phosphorus is also present in the two oils. While the quantity is lower in GL4, the amount fused in GL5 oil is much higher making it slightly more corrosive in nature.

Lead Amounts

While both of the oil types have lead present inside them, GL4 produces far less lead than GL5. As a matter of fact, the reason why there are high amounts of additives inside the GL5 is to reduce the effect that can be caused by the high amount of lead which is extremely toxic. 

Reaction With Metal

When it comes to reaction with8 metal, GL5 has shown great action. Although it won’t react readily with regular metal alloys, as long as copper, yellow metal, or brass is involved the result can often be disastrous.

GL4, on the other hand, is far less reactive since it has greater stability than the GL 5 gear oil.


Can You Use GL5 Gear Oil Instead of GL4?

If you have been using GL4 gear lube for some time now, then we advise you not to change your old GL 4 oil at all. This is because GL4 is far safer to use in the automotive axles than the GL5, despite GL5 having better brass synchro. Not only is it less reactive it is also far more environmentally friendly. 

However, that is not the answer to this question. Let’s suppose that you cannot find your regular GL4 oil in the market. In such cases, you can definitely use the GL5 oil. In fact, the GL5 oil is pretty decent albeit, not the best option.

However, do note that this is only for emergency situations. Use too much of the GL5 oil and your engine will start to damage your gearbox in the long run that is already used to the GL4 oil beforehand.


What Are Some Benefits of Using the GL5 Gear oil?

While we are advising you against using GL5 oil, there are certain advantages that you can still enjoy if you have been using GL5 for the first time instead of changing to it from GL4. 

  • We have compiled some of these benefits below that are commonly found associated with the use of GL5. 
  • The GL5 has been designed with extreme pressure that allows it to provide extra protection to the smaller gears from wear and tear due to time.
  • Although it has a high sulfur content, certain inhibitors have been used to give it an anti-rust property. 
  • The oil can be sealed quite easily so that it doesn’t leak out.
  • It has excellent stability against thermal and oxidation sources.
  • Foam inhibitors have been used to reduce the amount of occasional foaming. 


What Are the Benefits of Using GL4 Oil?

There are actually quite a lot of reasons why we are advising you to use the GL4 oil. We have pointed out some of these reasons via the listed data below. 

  • Great resistance against oxidation and rusting
  • High load capacity and can reduce wear and tear due to pressure in the gears.
  • Decent thermal durability.
  • The oil can be sealed quite easily so that it doesn’t leak out.
  • A good foam resistance property


Why Should You Change Your Gear Oil Regularly?

There are several reasons and advantages that you can experience if you change the gear oils at regular intervals. Some of these reasons have been compiled as follows:

Reduce Transmission Issues

It is quite common for oil to get contaminated and dirty with debris and dust particles from external sources as you drive your vehicle. As the particles accumulate this can cause your transmission performance to decrease. 

Changing the gear oil at regular intervals reduces the chances of such problems since the oil is cleaned out while the replacement.

Thermal Control Improvement

Thermal control is vastly connected to the transmission rate. This is because overaccumulation of dirt in the engine can cause the gear’s heat to upscale beyond control. 

However, with clean oil, you will not have to worry about overheating since the oil will make sure that the temperature of the gears returns to normal and no sparks are created when two gears come in contact with each other. 

Seamless Gear Shifting

Old contaminated synthetic oil can cause blockages in the cylinder and vents inside the engine even after you add extreme pressure additives for manual transmission fluid properties.

While simply oiling them again could give temporary relief, it is not a viable long-term option. 

You might sometimes notice that your gear is not shifting as smoothly as it is supposed to. The blocked cylinder and vents are the main cause of this issue. However, you are also advised to clean the vents beforehand.

Save Money

Replacing an entire engine or even small pieces of gear can take up a lot of money. So, if you decide to invest in good gear oil, you can save up a lot of money in the long run. 

Not only does the lubricant decrease corrosion and rusting in the engine, but it also increases the life expectancy of the engine gears.


What Are the Factors to Consider When Buying Gear Oil?

When you are going to buy oil, there are several things that you need to consider while buying. In this section, we will be giving you some of the factors that you need to understand before purchasing the right oil:


Location can also affect the type of oil you buy. This is because there are certain lubricants that are meant to be used for certain climates. If you use these oils in the summer, you won’t be able to use the oil’s potential to the full extent.

Viscosity Grade

The viscosity grade is the most important factor of the gear oil. If the viscosity doesn’t match the engine component requirements, this could result in sparks that will create a fire. Always check on the viscosity grade of your lubricant.

Check Label

The final tip is to check the label of the oil container that you are intending to buy. Find out whether the oils meet the right standards placed by either API or ACEA and have also been certified. It might not be wise to buy that oil if they don’t. 


Frequently Asked Questions

What does GL-5 stand for, and what does it mean?

The EP (Extreme Pressure) rating of a GL-5 grade oil is very high. Additives in EP gear oils help prevent metal surfaces from cold welding at the high pressures common in boundary lubrication.


How Often Should You Change the Gear Oil of Your Car?

Most automobiles’ gear oil may last up to 80,000 miles before being changed under normal driving circumstances. According to manufacturers, gear oil should be changed every 50,000 to 60,000 miles at the very most.


Why Do the Gears Need to Be Lubricated?

While there are plenty of reasons why you should frequently lubricate your gears, the main reason for lubrication is to reduce any chances of rusting while increasing engine output efficiency.


Is GL5 a bad thing for Synchros?

In this case, it’s more about what’s bad for your transmission than what’s suitable for your transmission. However, I wouldn’t rely on any GL5s that claim safe for the yellow metal.

Use GL4 instead of GL3. Every one of the first synchro transmissions is made entirely of the yellow metal.


Is GL4 a viable alternative to GL1?

Yes, GL4 is a suitable substitute for GL1. It’s got some more advanced technology that helps with wear, but not enough to create problems with “yellow metals,” so it’s truly an improvement.


Final Words

Well, after reading this article, you should have already chosen between GL4 vs GL5. Personally, we are still supporting GL4 as per our original statement. However, if you want a temporary substitute for some time, GL5 would make a decent choice. 

An alternative to both these oils could be the API GL 3 oil. You can consider this alternative as long as you can withstand the moderate speeds of your car with Motul gear.

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