How to Identify a Caterpillar C15 6NZ vs. MXS
(Fast Visual Guide)
Need to tell a 6NZ from an MXS in minutes? Here’s a quick, practical checklist using casting tags, valve covers, and emissions hardware so you can buy with confidence.
1) Valve Cover & Serial Prefix
- 6NZ: Pre-emissions single-turbo C15. ESN starts with 6NZ. Typically black composite valve cover.
- MXS: ACERT era twin-turbo. ESN starts with MXS. Often aluminum cover; emissions labels mention ACERT.
2) Turbo & Air Path
- 6NZ: Single turbo, simpler charge-air plumbing.
- MXS: Compound turbos (series). Look for two turbos and extra piping near right-rear of engine.
3) Sensors & Emissions Cues
- 6NZ: No VVA, no aftertreatment. Wiring is simpler; ECM strategies differ.
- MXS: ACERT features (VVA actuators, additional sensors). More harness plugs and solenoids on top/front.
Buyer Notes
- Verify ESN against the block stamping and ECM readout.
- Match flywheel housing, mounts, and fan hub to your chassis.
- Log baseline data after install: boost, pyrometer, oil pressure, and coolant delta-T.
