Match the API Category
Use CK-4 or FA-4 only where the engine manufacturer permits it. CK-4 is backward compatible; FA-4 is designed for selected newer engines and is not interchangeable with CK-4.
Class 8 Diesel Engines · USA & Canada
Best Semi Truck Oil for Class 8 Rigs
Choose heavy-duty diesel engine oil by the engine specification, viscosity, operating temperature and duty cycle—not by brand name or a universal mileage claim.
Direct answer
Most Class 8 diesel engines use an oil meeting API CK-4 in an OEM-approved viscosity such as 15W-40, 5W-40 or 10W-30. Some newer engines permit or require API FA-4, but FA-4 is not backward compatible. Always confirm the engine model, year and OEM specification before choosing the oil.
Last reviewed: July 2026 · Product claims checked against current AMSOIL technical literature supplied to SemiTruckOil.com
CK-4Backward-compatible diesel category
FA-4Only for engines that specifically permit it
3× OEM*Max-Duty heavy-duty on-/off-road service
60K mi max*Product-specific ceiling—not a generic synthetic interval
Start with the engine
There Is No Single Best Oil for Every Semi Truck
Cummins, Detroit, Paccar, Volvo, Mack, Caterpillar and International publish engine-specific oil requirements. The badge on the hood does not identify the correct lubricant by itself.
Match the OEM Specification
Confirm requirements such as Cummins CES 20086, Detroit DFS 93K222, Volvo VDS-4.5, Mack EOS-4.5 or the applicable Caterpillar specification.
Match Viscosity and Climate
15W-40 remains common, while 5W-40 improves low-temperature flow. Some modern engines specify 10W-30 or 5W-30. The operator's manual wins.
Do not use FA-4 by assumption. Confirm the engine model, build date and OEM approval. If FA-4 is not specifically permitted, use the correct CK-4 product and viscosity.
Viscosity
Common Semi Truck Engine Oil Grades
Temperature matters, but viscosity selection begins with the engine manufacturer's approved range.
| Viscosity | Typical role | Important restriction |
|---|---|---|
| 15W-40 | Common CK-4 grade for moderate and warm operating conditions. | Cold-start performance is lower than a 5W or 0W grade. |
| 5W-40 | CK-4 all-season choice where the OEM permits it; especially useful in Canadian winters. | Confirm the product carries the required OEM specification. |
| 10W-30 | Used in CK-4 and FA-4 formulations for selected modern engines and fuel-economy programs. | CK-4 10W-30 and FA-4 10W-30 are not the same category. |
| 5W-30 | Available in CK-4 and FA-4 formulations for applications calling for a lower-viscosity oil. | Read both the API category and OEM approvals—do not select by viscosity alone. |
| 0W-40 | Cold-climate CK-4 option where approved. | Use only when the engine manufacturer permits an SAE 0W-40. |
Selection process
How to Choose Semi Truck Oil
Identify the Engine
Record the engine family, model year, serial number and emissions generation.
Read the Requirement
Find the API category, OEM specification and permitted viscosity in current service information.
Account for Duty
Consider ambient temperature, line haul, vocational work, idling, fuel dilution and soot loading.
Verify the Product
Check the current lubricant data sheet before ordering or extending a drain interval.
AMSOIL diesel oils
Choose the Product for the Maintenance Program
These oils do not all have the same performance claims or service life. Match the product to the specification, engine and drain strategy.
Signature Series Max-Duty
DME · DEO · DTT · DHD · DZF
- 100% synthetic heavy-duty diesel oil
- 6X more wear protection than required by the Detroit Diesel DD13 Scuffing Test*
- Heavy-duty on-/off-road service: 3× OEM recommendation*
- Not to exceed 60,000 miles, 600 hours or one year—whichever comes first*
Heavy-Duty 100% Synthetic
ADP · ADO · ADN
- 100% synthetic formulation
- 4X more wear protection than required by the Detroit Diesel DD13 Scuffing Test*
- Meets multiple heavy-duty OEM specifications by grade
- Use the OEM-recommended drain interval unless supported by oil analysis
Heavy-Duty Diesel & Marine
AME 15W-40
- High-TBN 100% synthetic diesel oil
- Designed for pre-2007 diesel engines and other compatible applications
- Not intended for modern engines equipped with diesel particulate filters
- Confirm current product data and application before use
*AMSOIL Signature Series Max-Duty service life for heavy-duty on-/off-road diesel engines: three times the OEM recommendation, not to exceed 60,000 miles, 600 hours or one year, whichever comes first. Restrictions apply. Refer to the current AMSOIL product data sheet and the engine manufacturer's recommendations. The 6X wear claim is based on the Detroit Diesel DD13 Scuffing Test for specification DFS 93K222.
Drain intervals
Oil Type Alone Does Not Set the Change Interval
There is no supportable universal mileage for “full synthetic CK-4.” Service life depends on the exact product, engine, OEM schedule, duty cycle and lubricant condition.
| Oil or program | Service-life direction | What controls the interval |
|---|---|---|
| Conventional or synthetic blend | Follow the oil supplier and OEM recommendation. | Engine, duty cycle, time, fuel dilution and soot. |
| AMSOIL Heavy-Duty 100% Synthetic | Follow the OEM interval; extend only when supported by an oil-analysis program. | OEM guidance and analysis results. |
| AMSOIL Signature Series Max-Duty | Heavy-duty on-/off-road: 3× OEM, up to 60,000 miles, 600 hours or one year—whichever comes first.* | Product restrictions, OEM baseline and operating condition. |
| Shell Rotella T6 | Follow the engine manufacturer's and Shell's current published recommendation. | Verify the current Shell product data sheet; no fixed extended-drain mileage is stated here. |
Use oil analysis for confidence, not permission to ignore limits. Analysis can track viscosity, soot, fuel dilution, TBN, oxidation, contamination and wear metals. It does not cancel the product's maximum service life or the engine manufacturer's inspection requirements.
Engine pages
Find Oil Information by Diesel Engine
Use the engine-specific page as the starting point, then confirm the requirement by serial number and current OEM literature.
CumminsX15Oil specifications, viscosities and service considerations.
CumminsISX15CK-4 requirements and operating conditions.
DetroitDD13DFS specifications, CK-4 and FA-4 distinctions.
DetroitDD15Viscosity and emissions-generation considerations.
CaterpillarC15Pre-emissions and ACERT oil requirements.
MackMP8EOS and Volvo VDS-related specifications.
Whole-truck lubrication
Engine Oil Is Only One Part of the Maintenance Program
FAQ
Semi Truck Oil Questions
Answers are displayed in full so operators and search engines can read them without opening dropdowns.
What is the best oil for a semi truck?
The best oil is one that matches the engine's required API category, OEM specification and viscosity. Most Class 8 engines use CK-4, while selected newer engines permit FA-4. Check the engine serial number and current service information.
What weight oil does a semi truck use?
15W-40 is common, but 5W-40, 10W-30, 5W-30 and 0W-40 are used in appropriate applications. Climate matters, but the engine manufacturer's permitted viscosity range is the deciding factor.
How often should semi truck oil be changed?
Follow the engine manufacturer's interval and the oil manufacturer's product-specific service-life instructions. There is no universal synthetic-oil mileage. Oil analysis helps verify condition in a managed extended-drain program.
Can AMSOIL Max-Duty run 60,000 miles?
In eligible heavy-duty on-/off-road diesel service, AMSOIL Signature Series Max-Duty may be used for three times the OEM recommendation, not to exceed 60,000 miles, 600 hours or one year—whichever comes first. Restrictions apply, and the current data sheet must be followed.
Can CK-4 be used in an FA-4 engine?
CK-4 may be permitted in many engines that recommend FA-4, but the operator may lose the fuel-economy benefit intended by FA-4. Confirm the OEM's viscosity and category requirements before substituting.
Can FA-4 replace CK-4?
No. FA-4 has a lower high-temperature/high-shear viscosity and is not backward compatible. Use it only in engines that specifically permit FA-4.
Is full synthetic diesel oil worth it?
It can improve cold-flow, oxidation resistance and protection under severe temperature and load. The financial value depends on the product, maintenance interval, downtime and operating conditions—not on a generic mileage promise.
Does oil analysis allow unlimited drain intervals?
No. Analysis measures lubricant and engine condition, but published maximum mileage, hour and time limits still apply. It also does not override OEM inspection or warranty requirements.
One truck or a fleet
Match the Oil Before You Order
Use the heavy-duty lookup to confirm the engine, viscosity and AMSOIL product. Commercial operators can apply for business pricing and direct shipping.