Cox Powertrain – On Location – Testing & Development of the CXO300 Diesel Outboard Engine

A insight into Cox Powertrain’s Testing and Development team, talking through Cox’s high testing processes the CXO300 goes through before being delivered to the market.

The CXO300 is a new kind of diesel outboard and one of the most highly anticipated marine industry launches in decades. The 300hp diesel outboard has been designed from a blank sheet of paper by Cox Powertrain, to meet the needs of those who need diesel durability and fuel performance while maintaining the flexibility and performance of an outboard.

CXO300 Technical Data

Engine designation CXO300
Crankshaft power, kW (hp) 252 (338)
Propeller shaft power, kW (hp) 224 (300)
Engine propping speed, rpm 3700-4000
Displacement, L ( 4.4 (266)
Number of cylinders 8
Bore/stroke, mm (in.) 84 (3.3) / 98.5 (3.9)
Compression ratio 16
Weight, kg (lb) 375 (826)
Ratio 1 (Propeller speed) 1.23:1 (3259)
Ratio 2 (Propeller speed) 1.46:1 (2739)
Peak torque, Nm ( 650 (479)
Aspiration Twin-turbo
Shaft Length, inch(mm) 25”(635)/30”(762)/35”(889)
Emission compliance EPA 3, IMO 2, RCD 2
Start assist Glow plugs
Rating Light-duty commercial
Trim range -4° to +16°
Tilt range 71°
Engine Oil Spec API CI-4 / SAE 5W40
Gear Oil Spec API GL-5 / SAE 75W140
Propeller spline spec 1.25” shaft / 19 tooth
Colour options Black / White

CXO300 Technical Description

Engine block and head

  • Aluminium alloy block and heads
  • 60 degree V8

Engine mounting

  • Standard outboard fitting layout
  • 6-bolt mounting with multi-hole adjustment

Fuel system

  • High pressure common rail fuel injection
  • On-engine fuel filtration

Air inlet and exhaust system

  • Exhaust gas recirculation system
  • Twin turbochargers
  • Air filters with replaceable inserts
  • Closed crankcase ventilation


  • All outboards offer standard and counter rotating capability, programmable through the ECU

Cooling system

  • Thermostatically regulated raw water cooling
  • Tubular heat exchanger

Electric system

  • 12V/24V two-pole electrical system
  • 80A marine alternator

CXO300 Instructions & Controls


  • Seastar electronic controls
  • Seastar joystick to manage up to 6 engines
  • CoastKey keyless fob / wireless MOB technology
  • CAN J1939 Controls and Displays
  • Compatible with NMEA 2000
  • Murphy Powerview display – 4.8”/7”/11”/12”
  • Compatible with off the shelf Seastar steering units