The gear system plays a vital role in the performance of a semi truck.
Whether you’re a truck driver or a fleet owner, you must have known that the efficiency of the vehicle is directly related to proper maintenance; and that gear oil is a big piece.
There’s more to gear oil than you ever know. Some gear oils are helpful for your truck, and some are not. Thus, you can’t just pick and use every lubricant gear oil that you see in the market.
If you’re not familiar with gear oil, here’s a guide to appropriate gear oil maintenance.
Here’s a short summary of what gear oil can you use for semi trucks:
A semi truck uses mineral and synthetic gear oil. Mineral oil is commonly used for older trucks with corrosion issues, while synthetic gear oil is the standard lubricant nowadays. These lubricants can be used for the entire gear system, most importantly, for transmission and differential systems.
Table of Contents
Why do Semi Truck Gears Need Oil?
The metal-on-metal contact that the gear system is experiencing every time you use your truck causes wear and tear.
Gear oil protects the vehicle’s working parts by transferring heat and reducing friction when the truck operates.
Essentially, you need a gear oil to prolong the lives of a vehicle’s vital components like the gears, bearings, differentials, transmission, transfer cases, and a lot more.
Gear oil is crucial to every vehicle as it avoids costly repairs later on.
Is Transmission Fluid and Gear Oil the Same Thing?
Transmission fluid and gear oil are not the same. The easiest way to determine their difference is to identify their purpose.
As their names suggest, transmission fluid works on gears with automatic transmissions while gear oil has something to do with manual-gear boxes.
Automatic Transmission
Automatic transmission directly works on multiple automatic gears to answer numerous demands of an engine.
Typically, gear with automatic transmission is smaller yet greater in numbers than the manual gear system.
Transmission fluid lubricates and provides power to the clutches, the components responsible for the gear movement.
Manual Gear Box
Manual gearboxes feature two main components: gears and shafts. These components work together when the driver uses the clutch and gearstick.
When this happens, the entire gear system produces force, heat, and friction.
The gear oil makes the process seamless and smooth to prevent damage while the parts shift their positions.
What Gear Oil to Use for a Semi Truck?
The American Gear Manufacturers Association (AGMA) has classified two gear oils for industrial use. Industrial gear oils are common for trucks operating in harsh environments with heavy payloads.
These oils are synthetic and mineral oils.
Further, gear oils are also sub-classified as manual or automatic transmission oil, differential oil, and LSD gear oil.
Each oil works and provide benefits for each component. They also come with synthetic and mineral oil variants.
| Type of Gear Oil | Usage |
| Manual/Automatic Transmission Gear Oil | Helical Gear Double Helical Gear Spur Gear |
| Differential Gear Oil | Straight Bevel Gear Spiral Bevel Gear Hypoid Gear |
| LSD Gear Oil | Straight Bevel Gear Spiral Bevel Gear Hypoid Gear |
The differential synthetic gear oil is the most used lubricant for semi trucks. A differential oil, of course, lubricates the differential bearings, clutch packs, ring, and pinion gears.
Do Semi Trucks use Synthetic or Mineral Gear Oil?
Semi trucks use both synthetic and mineral gear oil. The use of this oil actually depends on user preferences and the recommendation of the vehicle manual.
However, nowadays, synthetic oil is most used by semi trucks for various reasons. In contrast, mineral gear oil is commonly used in older semi trucks.
Synthetic Oil
Synthetic oil has a higher viscosity than mineral oil. The oil remains thick and higher or lighter in high and low temperatures, respectively.
This results in a prolonged component life and makes it easy to start the engine.
Synthetic also provides less traction. This is a great advantage because it results in less heat and friction. This promotes fuel economy and energy efficiency.
Mineral Oil
Mineral oil refines crude petroleum. The process of refining the components removes rust, contaminants, unwanted impurities, and hydrocarbons. Hence, they are preferred by older semi trucks.
Moreover, mineral oil is less expensive than synthetic oil. They are commonly used by fleets and other large vehicles that prioritize volume than quality.
What Grade Gear Oil do Semi Trucks Use?
In general, oils are labeled with SAE grades. However, take note that gear oil usually has SAE grades of 50 and above.
You can determine the SAE grade of a gear oil product by looking at the viscosity under the specification.
Typically, semi trucks with low loads use 50 to 75 gear oil. Thanks to their thinner films and improved cooling capabilities, lower viscosity provides better protection for trucks with low loads.
In contrast, higher viscosity such as 75 and above is ideal for a truck operating with a large payload and off-road environment. High viscosity prevents corrosion and is known for wear resistance.
How much Gear Oil does a Semi Truck Take?
Overall, a semi truck can take up to 4 to 5 gallons or 15 to 18 liters of gear oil. However, having this much is not ideal because there’s only recommended oil intake for each component.
Check your vehicle’s manual for ideal oil intake.
Typically, a differential can hold up to 3 quarts or approximately 2 liters, while the transmission is about 9 to 13 quarts or approximately 8 to 12 liters.
How often should you Change Gear Oil?
There is no hard and fast rule as to when you should change gear oil in your semi truck. But if the vehicle’s manual provides the time for its maintenance, you must follow it.
Some truck manufacturers recommended the change of gear oil after hitting 50,000 to 60,000 miles.
If you want to establish your own gear oil maintenance routine, it’s ideal for changing the oil between 30,000 to 50,000 miles for automatic trucks.
However, for manual trucks, a distance of 60,000 to 100,000 miles is recommended.
If the truck is used in severe conditions like towing, hauling, and construction work in mud or off-road, you need to change the oil after reaching 15,000 miles.
What is the Best Transmission Fluid?
With many products claiming to be the best, it’s pretty challenging to find which one is truly the best.
To help you find the one suitable for your truck needs, we have come up with the best transmission fluid you can avail of:
- Best of the Best – Castrol Transmax Dex/Merc
- Best for Value – Mobil 1 Synthetic Automatic Transmission Fluid
- Honorable Mention – Valvoline Full Synthetic Automatic Transmission Fluid
What kind of Oil goes in a Semi Truck Differential?
You should use gear oil for your semi trucks differential. The type of gear oil, however, could be mineral or synthetic oil.
The mineral differential oil is a natural lubricant used to prevent corrosion, while the synthetic oil is meant to achieve optimum performance.
Most newer and automatic trucks may require synthetic oil, while older trucks may need mineral oil.
Can you use Transmission Fluid for Differentials?
You can use transmission fluid for differential, but you have to be cautious to use the latter for transmissions.
Transmission fluid is somewhat the same as gear oil. It can be used to lubricate the whole drivetrain – differential, driveshafts, clutch, and gearboxes.
Further, while some products have been labeled “for differential and transmission use,” this may not be good for transmission because of high grade or viscosity.
It may damage the transmissions and it may cause clogging in between the components.
It’s recommended that you buy or use differential oil for differential and transmission fluid for transmission.
Do Semi Trucks Differentials Use Synthetic or Mineral Oil?
As previously mentioned, semi trucks both use synthetic and mineral oil.
However, since most semi trucks are used for extreme zones and high loads, synthetic oils are commonly used.
The most obvious reasons why trucks use synthetic are fuel efficiency, safety, and service life.
Overall, synthetics are designed for excellent performance. The only downside of which is its expensive price.
What Grade Differential Oil do Semi Trucks Use?
Most differential gear oils require a grade of SAE 75w90. In comparison, some heavy-duty semi trucks may require SAE 90, 80w-90, and 75w140.
Refer to the vehicle’s manual to which type of oil and grade is appropriate for your semi trucks.
How much Differential Oil does a Semi Truck Take?
On average, a semi truck can take up to 3 quarts of differential oil. Again, this is only the usual capabilities of a semi truck, and it may vary depending on the size of the truck and number of differentials a vehicle has.
To be sure, check the vehicle’s manual as the weight and capacity of the differential will be listed there.
How often should you Change Differential Oil?
Overall, the oil change for differentials should be done every time the vehicle reaches 30,0000 to 60,000 miles. However, for the front differential, oil changes should be about 25,000 to 35,000 miles.
If the truck manufacturer provides otherwise, follow such recommendation.
In addition, oil changing is a messy job. It is advised that you let professional mechanics do this maintenance routine.
What is the Best Oil for the Differential?
It’s not difficult to find the best oil for differential as the market is bombarded with high-end brands.
The only problem is when the one you may choose is not appropriate for your truck.
So we give you the best differential oils your truck can make use of:
- Best of the Best: Red Line Synthetic Oil 75W90
- Best for Value: Mobil Delvac Gear Oil 75W90
- Honorable Mention: Liqui Molly Fully Synthetic Gear Oil
Some gear oil products may indicate that they can be used for several purposes (e.g., differential, transmission).
If you wish to save some money, you can avail of them but be mindful of the SAE grade advised by your manufacturer.
Some oil may cause more damage than help, so you must make better choices. After all, repair costs are more expensive than regular maintenance.