Engine Oil Spec

PACCAR MX-11 Engine Oil

PACCAR MX-11 engine oil spec is API CK-4, 15W-40 primary grade, 34 qt (8.5 gal) capacity with filter.
FA-4 is not approved for this engine. OEM drain interval is 25,000 miles highway.

⛔ FA-4 NOT APPROVED — Use API CK-4 only. Do not substitute FA-4 in an MX-11.

OEM Oil Spec

CK-4

API Standard

Primary Grade

15W-40

Standard conditions

Oil Capacity

34 qt

8.5 gal w/ filter

OEM Drain — Highway

25K mi

Normal service

Severe Service

15–20K

Miles (vocational/PTO)

FA-4 Approved

CK-4 only

Quick Spec — PACCAR MX-11

Engine	PACCAR MX-11 Inline-6
Displacement	10.8L
Applications	Kenworth T680, T880, W990 · Peterbilt 389, 579, 567
OEM Oil Spec	API CK-4
Primary Grade	15W-40
Cold Weather Grade	10W-30 CK-4 (above −4°F / −20°C)
Oil Capacity	34 qt (8.5 gal) with filter
FA-4 Approved	NO — CK-4 only

Viscosity Grade — What to Run

PACCAR specifies a single path for the MX-11: CK-4. No FA-4. No proprietary overlay beyond the API standard. Pick the right weight for your temps.

15W-40

Primary Grade Recommended

Run this in all standard operating conditions. Covers most of the continental US year-round and all summer/warm-weather operation. Full synthetic 15W-40 CK-4 delivers the best protection and drain interval.

10W-30

Cold Weather Alternative

Acceptable when ambient temps are consistently above −4°F (−20°C). Must be CK-4 rated. Offers easier cold cranking in winter without sacrificing wear protection. Switch back to 15W-40 when temps climb.

FA-4

Not Approved

FA-4 carries a lower HTHS (high-temperature/high-shear) viscosity than CK-4. The MX-11 is not engineered for this profile — using FA-4 risks inadequate film thickness under load. PACCAR does not approve it for this engine.

Bottom line: 15W-40 CK-4 full synthetic is the right call for MX-11 operators in most of the US. Cold-start protection in northern winters? Drop to 10W-30 CK-4. FA-4 isn’t on the table.

OEM Drain Intervals — MX-11

OIL CHANGE INTERVAL BY SERVICE TYPE (MILES)

Highway OEM

25,000 mi

Severe Service

15–20K mi

Extended (Synthetic + UOA)

50,000+ mi

Highway / Normal	25,000 miles — standard OEM interval for over-the-road operation
Severe Service	15,000–20,000 miles — vocational, PTO use, stop-and-go, construction, heavy idle
Extended Drain	50,000+ miles — requires CK-4 full synthetic + used oil analysis (UOA) at each interval

Extended drains: Achievable with a top-tier CK-4 full synthetic and a UOA program. Used oil analysis confirms your oil is still in spec before you push past the OEM interval — don’t skip it.

AMSOIL Products — Approved for MX-11

Both options below are CK-4 certified and a direct fit for the MX-11. The primary pick handles the longest drain intervals. The value pick adds Allison TES-295 coverage for mixed fleets.

Primary Pick

Signature Series Max-Duty 15W-40

Part #DME

API CK-4 certified
Up to 60,000-mile drain interval
6× better wear protection vs. conventional
Full synthetic formulation
Best-in-class for extended UOA programs

Shop DME — Signature Series

Value Pick

Heavy-Duty Synthetic Diesel Oil 15W-40

Part #ADP

API CK-4 certified
Allison TES-295 approved
Full synthetic protection
Strong wear and oxidation resistance
Good fit for mixed fleets with Allison trans

Shop ADP — Heavy-Duty Synthetic

FAQ — PACCAR MX-11 Oil

What oil does a PACCAR MX-11 take?

The PACCAR MX-11 takes API CK-4 engine oil. The primary viscosity grade is 15W-40. There is no PACCAR-proprietary oil specification beyond the CK-4 standard — any CK-4-certified 15W-40 meets the spec. FA-4 is not approved and should not be used in this engine.

How much oil does a PACCAR MX-11 hold?

The PACCAR MX-11 holds 34 quarts (8.5 gallons) of engine oil including the filter. Always fill to the upper mark on the dipstick and confirm level before startup after a drain-and-fill.

Can you use FA-4 oil in a PACCAR MX-11?

No. FA-4 is not approved for the PACCAR MX-11. FA-4 oils carry a lower HTHS (high-temperature/high-shear) viscosity than CK-4 — a profile designed specifically for engines engineered to accept it. The MX-11 is not one of them. Using FA-4 risks insufficient oil film thickness under load. Stick with CK-4.

What is the oil change interval for a PACCAR MX-11?

The OEM drain interval is 25,000 miles for highway operation. Severe service — vocational, heavy idle, PTO, construction — drops that to 15,000–20,000 miles. Running a CK-4 full synthetic with used oil analysis (UOA) can extend drains to 50,000+ miles. UOA is not optional for extended drain programs — pull a sample and verify the oil is still in spec.

What is the difference between the PACCAR MX-11 and MX-13?

The MX-11 displaces 10.8L and produces up to 430 hp — built for regional haul, vocational work, and medium-long distance applications where weight savings matter. The MX-13 displaces 12.9L with outputs up to 510 hp, targeting heavy-duty long-haul where maximum power and torque are the priority. Both engines require API CK-4 oil at 15W-40, but oil capacities differ.

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