Comparison
AMSOIL vs Mobil Delvac MX
Premium Synthetic vs Conventional Blend — What the Difference Costs You
Mobil Delvac MX 15W-40 is a conventional/mineral-based diesel oil meeting API CK-4 minimum requirements. AMSOIL Signature Series Max-Duty (DME) is a full synthetic meeting CK-4 with significantly broader OEM approvals and extended drain capability. The comparison is not purely product vs product — it’s also conventional vs synthetic and standard drain vs extended drain.
Understanding the Products
Mobil’s Delvac line spans multiple tiers. Delvac MX is the conventional/mineral oil entry point — widely available, straightforward CK-4 compliance, no proprietary OEM approvals. Delvac 1 ESP is Mobil’s premium full synthetic (a separate comparison covers that). This page covers Delvac MX specifically.
AMSOIL Signature Series Max-Duty (DME) is a 100% full synthetic 15W-40 formulated for extended drain intervals with proprietary OEM approval coverage across major North American fleet manufacturers.
Head-to-Head Comparison
| Feature | AMSOIL DME | Mobil Delvac MX |
|---|---|---|
| Base oil | Full synthetic | Conventional/mineral |
| API | CK-4 | CK-4 |
| CES 20086 (Cummins) | Yes | No |
| DFS 93K222 (Detroit GHG17) | Yes | No |
| VDS-4.5 (Volvo) | Yes | No |
| EOS-4.5 (Mack) | Yes | No |
| MB 228.51 | Yes | No |
| Extended drain | Yes — 50K+ with analysis | No — 15K standard |
| Cold start protection | Superior (full synthetic) | Standard |
| Oxidation resistance | Superior | Standard |
| Price per quart | Premium | Budget |
| TCO (highway fleet) | Lower (extended drain) | Higher (frequent changes) |
OEM Approvals — Why They Matter
CK-4 is the floor — the minimum API category for current heavy-duty diesel engines. Proprietary OEM specifications like DFS 93K222 (Detroit), CES 20086 (Cummins), and VDS-4.5 (Volvo) go beyond CK-4 with additional testing requirements specific to each manufacturer’s engine architecture.
For GHG17 Detroit DD-series engines: DFS 93K222 approval is required for extended drain intervals and warranty compliance. Delvac MX meets CK-4 minimum but does not carry DFS 93K222 approval.
For Cummins X15 engines: CES 20086 carries specific requirements around seal compatibility and oxidation. Delvac MX does not carry this approval.
When Delvac MX Makes Sense
Fair Assessment
For older pre-emissions engines without proprietary spec requirements — or for operators with very short drain intervals (severe service, construction, mining) where extended drain capability doesn’t apply — Delvac MX is a functional, low-cost option. If you’re changing oil every 10,000 miles regardless, the extended drain premium of full synthetic doesn’t pay back. Know your application.
Extended Drain and TCO
At 50,000 miles, AMSOIL DME requires one oil change. Delvac MX at 15,000-mile intervals requires three. Factor in filter cost, labor, and downtime — for highway operators, the synthetic premium typically pays back within the second drain interval.
For fleets with short drain intervals due to application or duty cycle, this TCO argument weakens. The correct oil for your operation depends on how you operate, not just what the engine nameplate says.
AMSOIL Signature Series Max-Duty (DME)
Full synthetic CK-4. Approved for DFS 93K222, CES 20086, VDS-4.5, EOS-4.5, and MB 228.51. Extended drain capable with oil analysis. Covers the full range of major North American fleet OEM specifications in a single product.
Frequently Asked Questions
Is AMSOIL better than Mobil Delvac MX?
For modern Class 8 engines with proprietary OEM specs (DFS 93K222, CES 20086, VDS-4.5): yes, significantly. Delvac MX does not carry these approvals. For older pre-emissions engines running standard drain intervals, both meet CK-4 — the premium is less justified.
Does Mobil Delvac MX meet DFS 93K222?
No. Delvac MX is a conventional oil meeting CK-4 minimum. Detroit’s DFS 93K222 specification requires additional testing beyond API CK-4 compliance. Products must be individually approved by Detroit Diesel to carry DFS 93K222 status.
Can I use Delvac MX in a GHG17 Detroit?
It meets the API CK-4 floor, but it doesn’t carry DFS 93K222 approval. For warranty compliance and extended drain eligibility on a GHG17 DD15, you need a DFS 93K222 approved product. AMSOIL DME carries that approval.