PACCAR MX-13 — 12.9L Inline-6
PACCAR MX-13 Engine Oil — Spec, Capacity & Change Interval
The PACCAR MX-13 is the 12.9L engine in Kenworth and Peterbilt trucks, rated 405–510 hp and up to 1,850 lb-ft. PACCAR keeps the oil spec simple: API CK-4, no proprietary overlay, and FA-4 is not approved. Most of what's published about MX-13 oil gets two things wrong: the grade (PACCAR recommends 10W-30, not 15W-40) and the drain interval (up to 75,000 mi, not 25,000).
Last reviewed: October 2026 · Based on PACCAR service literature (TIB E256, MX engine service intervals) and AMSOIL data sheet G3467
A PACCAR MX-13 holds 42 quarts (40 L, 10.5 US gallons). PACCAR recommends SAE 10W-30 API CK-4; 15W-40 CK-4 is also allowed, and FA-4 is not approved. PACCAR's oil change interval runs from 30,000 mi in severe service to 75,000 mi in line haul with under 20% idle. Red Seal tech pick for the MX-13: AMSOIL Max-Duty 10W-30 (DTT).
Capacity
Inline-6
Recommended Grade
Line Haul <20% Idle
MX-13 Oil Spec — 10W-30 CK-4, Not FA-4
PACCAR specifies API CK-4 for the MX-13 and recommends SAE 10W-30 (PACCAR TIB E256, December 2019). 15W-40 CK-4 is also allowed. FA-4 oils are not approved in the MX-13, so a "fuel-economy" FA-4 5W-30 or 10W-30 is the wrong oil for this engine.
- Oil SpecAPI CK-4
- SourcePACCAR TIB E256
- StatusRecommended by PACCAR
- Cold StartsEasier than 15W-40
- Full OEM Intervals?Yes — up to 75K mi
- AMSOIL ProductDTT 10W-30
- Oil SpecAPI CK-4
- When It FitsMixed fleets on 15W-40
- Trade-offSlower cold-start flow
- FA-4 Allowed?No — CK-4 only
- Full OEM Intervals?Yes, on CK-4
- AMSOIL ProductDME 15W-40
No PACCAR-only spec to chase: unlike Cummins (CES 20086), Detroit (DFS 93K222) or Volvo (VDS-4.5), PACCAR uses the API CK-4 category directly. Look for "API CK-4" on the jug and pick the viscosity.
⚠ Do not use FA-4 in an MX-13. PACCAR approves CK-4 only. And a 2017-or-newer MX-13 run on older CJ-4 oil drops back to PACCAR's shorter EPA13 drain intervals.
PACCAR MX-13 Oil Capacity
The MX-13 oil system holds 42 US quarts (40 L, 10.5 gallons), per PACCAR's MX-13 spec sheet. The smaller MX-11 holds 39 quarts. Older guides that list the MX-13 at 43 quarts or more are off; buy for 42 at a normal oil and filter change.
| Engine | Quarts | Litres | Gallons | Notes |
|---|---|---|---|---|
| MX-13 Oil System | 42 qt | 40 L | 10.5 gal | PACCAR MX-13 spec sheet |
| MX-11 Oil System | 39 qt | 37 L | 9.75 gal | For comparison |
⚠ Always verify capacity with your engine's service label and dipstick. Overfilling causes oil foaming, aeration, and seal damage. Underfilling reduces oil pressure margin under high load.
Buy the Right Oil for an MX-13 Service
A PACCAR MX-13 holds 42 quarts, about 10.5 US gallons. Two AMSOIL Twin Packs plus one gallon jug is 11 gallons: one full service with 2 quarts left for top-offs. PACCAR recommends 10W-30 API CK-4, and one 55-gallon drum covers five MX-13 services.
- The viscosity PACCAR recommends for the MX-13
- One service: 2 Twin Packs (DTTTP-CA) + 1 gallon jug (DTT1G-EA) = 11 gal
- The Red Seal tech pick for every MX-13
- A viscosity PACCAR lists for the MX-13
- One service: 2 Twin Packs (DMETP-CA) + 1 gallon jug (DME1G-EA) = 11 gal
- One oil if the rest of your fleet runs 15W-40
- Lower cost per service than jugs
- One 55-gallon drum covers five MX-13 services
- Shipped direct to your shop or yard
Run PACCAR's interval for your duty cycle (up to 75,000 mi in line haul with under 20% idle). Want to go past it? Do it on oil analysis, not guesswork. Get an Oil Analysis Kit →
MX-13 Oil Change Interval
PACCAR sets the MX-13 oil and filter interval by duty cycle and idle time, on API CK-4 oil: 75,000 mi, 2,250 hours or 12 months in line haul with under 20% idle; 50,000 mi, 1,500 hours or 12 months in line haul with over 20% idle; and 30,000 mi, 800 hours or 12 months in severe or vocational service. Whichever comes first.
(121,000 km) or 2,250 hr
(80,000 km) or 1,500 hr
(48,000 km) or 800 hr
line haul · 20,000 mi severe
⚠ Going past PACCAR's interval? Do it on oil analysis. PACCAR's own MX-13 interval already reaches 75,000 mi in line haul. A good synthetic gives you more margin inside that interval. Going beyond it safely takes a lab report on your own truck, because idle time, biodiesel blends, EGR cooler leaks and soot loading all shorten oil life.
FA-4 vs CK-4 on the MX-13
CK-4 only. PACCAR approves API CK-4 for the MX-13 and does not approve FA-4. That makes the MX-13 different from a GHG17 Detroit, where FA-4 is an option. If your shop stocks an FA-4 oil for Detroits, keep it out of the Kenworths and Peterbilts.
CK-4 — Approved
- ✓ PACCAR's oil category for the MX-13
- ✓ 10W-30 recommended, 15W-40 allowed
- ✓ Qualifies for PACCAR's full drain intervals
- ✓ Backward compatible with older diesel engines
FA-4 — Not Approved
- ✗ Not approved by PACCAR for the MX-13
- ✗ Lower HTHS viscosity than CK-4
- → Built for engines designed around it
- → Easy to grab by mistake in a mixed shop
Simple rule: MX-13 = API CK-4, 10W-30 or 15W-40. Never FA-4. AMSOIL's heavy-duty diesel oils are all API CK-4, so every Max-Duty grade meets that requirement.
Does PACCAR Have Its Own Oil Spec?
No. PACCAR uses the API CK-4 category directly instead of publishing its own oil spec the way Cummins, Detroit, Mack and Volvo do. That makes buying simpler, but it doesn't make every CK-4 oil equal: the additive package decides how much margin you have at 50,000 or 75,000 miles.
Shear Stability
Oil must hold its viscosity grade under heavy mechanical shear.
Oxidation Resistance
CK-4 added tougher oxidation testing for long drains and high heat.
Soot Handling
Oil must keep EGR soot suspended so it can't thicken the oil or wear parts.
Aeration Control
Oil must resist air entrainment that weakens the oil film.
| Category | MX-13 Status | HTHS | Viscosity |
|---|---|---|---|
| API CK-4 | Approved — full intervals | ≥ 3.5 cP | 10W-30 (recommended), 15W-40 |
| API CJ-4 | Older category — EPA13 intervals in 2017+ engines | ≥ 3.5 cP | Superseded by CK-4 |
| API FA-4 | Not approved | 2.9–3.2 cP | Do not use |
Best AMSOIL Oil for the PACCAR MX-13
For the MX-13, the Red Seal tech pick is AMSOIL Signature Series Max-Duty 10W-30 (DTT), a CK-4 oil in the viscosity PACCAR recommends. Max-Duty 15W-40 (DME) is the choice if your fleet standardizes on 15W-40, and Max-Duty 5W-30 (DHD) covers mixed fleets that need one oil for every make.
- API CK-4, the category PACCAR specifies
- PACCAR's recommended viscosity
- Strong high-temperature film protection (HTHS 3.5)
- Up to 76% less oil consumption than API CK-4 allows
- API CK-4, a viscosity PACCAR allows
- Also meets Cummins CES 20086 and DFS 93K222
- Highest HTHS in the Max-Duty line (4.5)
- API CK-4, not FA-4
- Also meets CES 20086, DFS 93K222, EOS-4.5, VDS-4.5
- Cold cranking to −30°C (−22°F)
Use the AMSOIL heavy-duty lookup to cross-reference your engine make, model, year, and emissions tier.
Use the AMSOIL Heavy-Duty Lookup →AMSOIL MX-13 Oil — Which Tier Is Right for You?
Not every truck or budget calls for the same product. AMSOIL makes multiple diesel oil tiers depending on the job.
| Product | Protection Level | Drain Interval | Best For |
|---|---|---|---|
| Signature Series Max-DutyDTT / DME / DHD | Top-tier synthetic diesel protection | OEM interval; beyond it with oil analysis | Owner-operators and fleets maximizing uptime |
| Heavy-Duty SyntheticADN / ADP | Full synthetic protection | OEM interval | Operators wanting synthetic protection at lower upfront cost |
| Commercial-GradeSBDT / SBDF | Synthetic-blend upgrade | OEM interval | Fleets upgrading from conventional oil |
All three tiers are API CK-4 oils, the category PACCAR specifies. Run PACCAR's interval for your duty cycle, and use oil analysis before going past it.
Why MX-13 Fleets Should Run Oil Analysis
The MX-13 runs EGR, and idle time changes how fast oil wears out. PACCAR builds idle into its own intervals for that reason. Mileage alone does not tell you the full story.
A basic oil analysis sample checks the numbers that matter:
- → TBN: remaining acid-neutralizing reserve
- → Soot: soot loading and viscosity risk
- → Fuel dilution: idle time and biodiesel thin the oil
- → Coolant contamination: early warning for cooler or gasket problems
Cross 20% idle and PACCAR cuts the MX-13 interval from 75,000 to 50,000 miles. Long idle hours load the oil with soot and fuel without adding miles.
Oil analysis shows what idle is actually doing to your oil, truck by truck.
| Analysis kit | A fraction of one oil change |
| Early coolant leak detection | Major repair avoided |
| Confirmed drain extension | Fewer oil changes |
| Wear metal trending | Rebuild risk reduced |
PACCAR MX-13 Engine Oil — Common Questions
From owner-operators, fleet managers, and shop techs running the MX-13 in Kenworth and Peterbilt trucks across North America.