AMSOIL guide
AMSOIL Diesel Oil Guide
AMSOIL builds three families of diesel engine oil: Signature Series Max-Duty for the longest-drain option in the lineup, Heavy-Duty 100% Synthetic for severe service at a more accessible price, and Commercial-Grade for fleet operators who want a synthetic-blend value pick. Pick the family by service plan and budget, then confirm the viscosity and current approvals through the live AMSOIL lookup and your owner's manual.
Shop AMSOIL Signature Series Max-Duty 5W-40
AMSOIL diesel oil lineup at a glance
| Family | Drain interval target | Best fit | Where to buy |
|---|---|---|---|
| Signature Series Max-Duty 5W-40 (DEO) | Longest-drain diesel option in the lineup | Power Stroke, Cummins, Duramax in cold or mixed climates | Buy online | Product details |
| Signature Series Max-Duty 15W-40 (DME) | Longest-drain diesel option in the lineup | Warm-climate fleets, hot-running engines | Buy online | Product details |
| Heavy-Duty 15W-40 (ADP) | OEM-recommended interval | Severe-service trucks at a lower price than Max-Duty | Buy online | Product details |
| Commercial-Grade 15W-40 (SBD) | OEM-recommended interval | Fleet value pick, synthetic-blend formulation | Buy online | Product details |
Match your owner's manual first
Every modern diesel engine ships with a specific viscosity grade and an API service category called out in the owner's manual. Common examples include API CK-4 for current pickups, API CJ-4 for emissions-equipped trucks from roughly 2007 through 2016, and API CI-4 or older for pre-emissions engines.
Some engine builders also list proprietary approvals that can change as oil formulas and factory requirements evolve. Match the API category and any OEM approval through the current AMSOIL product page before you compare brands. Running a lower-grade oil than the manual calls for can void warranty coverage and damage aftertreatment hardware.
Pick the right viscosity grade
For most modern North American diesel pickups, the common choice is between 5W-40 and 15W-40. Use the live AMSOIL lookup result and your owner's manual to confirm the current viscosity and approval match for your engine before ordering.
For newer engines that specifically list API FA-4, use only an FA-4 oil; FA-4 is a fuel-economy oil that is not interchangeable with the broader CK-4 category. The diesel motor oil overview covers the full viscosity range with side-by-side spec comparisons.
Match the oil to your emissions hardware
Trucks with diesel particulate filters, selective catalytic reduction, or exhaust gas recirculation require low-SAPS, low-ash oils. API CK-4 and API FA-4 oils are designed for these aftertreatment systems and protect the catalyst and particulate filter from premature contamination.
Avoid pre-2007 oil categories such as CI-4 in any modern emissions-equipped truck. Older oils carry higher sulfated ash, phosphorus, and sulfur, which shorten the life of the diesel particulate filter and reduce sensor accuracy.
Set the drain interval with oil analysis
AMSOIL Signature Series Max-Duty Synthetic Diesel Oil is engineered for extended service when paired with oil analysis and the right filter. Follow the current AMSOIL product guidance, your owner's manual, and oil-analysis results before extending a drain schedule. Pair any extended service plan with an AMSOIL Ea-O extended-drain oil filter.
Bottom line: which AMSOIL diesel oil should you pick?
- 6.7L Power Stroke, 6.7L Cummins, or L5P Duramax in cold or mixed climates. Pick Signature Series Max-Duty 5W-40 (also online from AMSOIL).
- Warm-climate fleet or hot-running engine. Pick Signature Series Max-Duty 15W-40 (also online from AMSOIL).
- Severe-service truck on the OEM interval at a lower price. Pick Heavy-Duty 15W-40 (also online from AMSOIL).
- Fleet value pick, synthetic-blend formulation. Pick Commercial-Grade 15W-40.
Save on AMSOIL with Preferred Customer pricing
AMSOIL Preferred Customer membership is $20 USD per year ($10 USD for a six-month trial) and unlocks up to 25% off on every product, with free shipping on qualifying orders. Add the membership to the same cart as your order and qualifying products switch to member pricing on that checkout, with no separate sign-up step. See the breakdown on the AMSOIL Preferred Customer page, or sign up directly through the AMSOIL Preferred Customer enrollment page.
AMSOIL diesel oil FAQ
What is the best AMSOIL diesel oil for a 6.7L Power Stroke?
AMSOIL Signature Series Max-Duty Synthetic Diesel Oil 5W-40 is a common pick for the Ford 6.7L Power Stroke when the live AMSOIL lookup confirms the match. The 5W-40 viscosity gives stronger cold-start performance than 15W-40 in winter climates where the truck sits overnight at sub-freezing temperatures.
Can I run 5W-40 instead of 15W-40 in my Cummins or Duramax?
Yes in most cases. Cummins and GM Duramax owner's manuals list both 5W-40 and 15W-40 as approved viscosity grades for current model years. 5W-40 is preferred below freezing and during long idle warmups, while 15W-40 is common in warm-climate fleets. Always verify with the chart in your specific owner's manual.
Is API FA-4 the same as API CK-4?
No. API FA-4 is a fuel-economy oil designed for newer model-year on-highway diesel engines that specifically call for FA-4. API CK-4 is the broader heavy-duty category and covers most current pickups, fleet trucks, and off-road diesels. Use only what your owner's manual lists; running FA-4 in a CK-4 application can damage the engine.
How long does AMSOIL Signature Series Max-Duty Diesel last?
For extended diesel service, follow the current AMSOIL product-page guidance, the engine manual, and oil-analysis results. Verify with a sample at the planned interval before stretching longer.
Does AMSOIL diesel oil work with DPF and SCR systems?
Yes. The AMSOIL Signature Series Max-Duty and Heavy-Duty API CK-4 lines are low-SAPS, low-ash formulations designed for diesel particulate filters and selective catalytic reduction. Older API CI-4 oils are not safe for current emissions hardware.
Where can I see all AMSOIL diesel oil viscosities?
The full lineup lives on AMSOIL's diesel engine oil page, filterable by viscosity. The matching diesel motor oil overview covers the same lineup with side-by-side spec comparisons.
Order AMSOIL diesel oil
Order online from AMSOIL's diesel engine oil page. To unlock up to 25% off, add an AMSOIL Preferred Customer membership to the same cart and qualifying products switch to member pricing immediately, with no separate sign-up step.