The Cat 3126B Marine Engine (produced between 1998 and 2003) represents a modernized, electronically controlled marine diesel platform derived from the proven Caterpillar 3126 line. Designed for marine propulsion and auxiliary power applications, the 3126B delivers a broad range of power ratings while maintaining reliability, ease of maintenance, and fuel-efficient operation.
Cat 3126B Marine 250 bhp / 275 bhp Specs and Curves
| Engine |
CAT 3126B Marine, 250 bhp (186 bkW), DM7370-00 |
CAT 3126B Marine, 275 bhp (205 bkW), DM7371-00 |
| Number of Cylinders |
6 |
6 |
| Displacement |
442 cu in (7.2 L) |
442 cu in (7.2 L) |
| Bore |
4.33 in (110 mm) |
4.33 in (110 mm) |
| Stroke |
5.00 in (127 mm) |
5.00 in (127 mm) |
| Max Power |
250 bhp (186 kW) |
275 bhp (205 kW) |
| Power Measured |
2400 rpm |
2400 rpm |
| Peak Torque |
727 lb ft (986 Nm) |
802 lb ft (1088 Nm) |
| Torque Measured |
1800 rpm |
1800 rpm |
| Governor |
Electronic |
Electronic |
| Flywheel and Housing |
SAE No. 3 (126 teeth) |
SAE No. 3 (126 teeth) |
| Starter |
12 V |
12 V |
| Alternator |
51 amps, 12 V |
51 amps, 12 V, belt driven |
| Rotation (from flywheel end) |
CCW |
CCW |
| Air Cleaner |
Air cleaner with fumes disposal (closed system) |
Air cleaner with fumes disposal (closed system) |
| Fuel Consumption |
12.9 gal/h (48.9 L/h) @2400 rpm |
14.0 gal/h (53.1 L/h) @2400 rpm |
| Aspiration |
Turbocharged Aftercooled |
Turbocharged Aftercooled |
| Exhaust system |
Watercooled exhaust manifold |
Watercooled exhaust manifold and turbocharger |
| Emission Standards |
IMO I emissions level (2000-2010) |
IMO I emissions level (2000-2010) |
- 3126B DM7370-00 (250 bhp / 254 mhp / 186 bkW @2400 rpm) - Light-duty workboats, tenders, auxiliary power, small commercial craft.
- 3126B DM7371-00 (275 bhp / 279 mhp / 205 bkW @2400 rpm) - Mid-range workboats, small coastal fishing boats, coastal commercial vessels.
Cat 3126B Marine 315 bhp / 370 bhp Specs and Curves
| Engine |
CAT 3126B Marine, 315 bhp (235 bkW), DM7372-00 |
CAT 3126B Marine, 370 bhp (276 bkW), DM7398-00 |
| Number of Cylinders |
6 |
6 |
| Displacement |
442 cu in (7.2 L) |
442 cu in (7.2 L) |
| Bore |
4.33 in (110 mm) |
4.33 in (110 mm) |
| Stroke |
5.00 in (127 mm) |
5.00 in (127 mm) |
| Max Power |
315 bhp (235 kW) |
370 bhp (276 kW) |
| Power Measured |
2400 rpm |
2600 rpm |
| Peak Torque |
919 lb ft (1246 Nm) |
1080 lb ft (1464 Nm) |
| Torque Measured |
1800 rpm |
1800 rpm |
| Governor |
Electronic |
Electronic |
| Flywheel and Housing |
SAE No. 3 (126 teeth) |
SAE No. 3 (126 teeth) |
| Starter |
12 V |
12 V |
| Alternator |
51 amps, 12 V |
51 amps, 12 V, belt driven |
| Rotation (from flywheel end) |
CCW |
CCW |
| Air Cleaner |
Air cleaner with fumes disposal (closed system) |
Air cleaner with fumes disposal (closed system) |
| Fuel Consumption |
17.0 gal/h (64.4 L/h) @2400 rpm |
20.5 gal/h (77.5 L/h) @2600 rpm |
| Aspiration |
Turbocharged Aftercooled |
Turbocharged Aftercooled |
| Exhaust system |
Watercooled exhaust manifold |
Watercooled exhaust manifold and turbocharger |
| Emission Standards |
IMO I emissions level (2000-2010) |
IMO I emissions level (2000-2010) |
- 3126B DM7372-00 (315 bhp / 319 mhp / 235 bkW @2400 rpm) - Larger fishing or passenger craft, utility vessels, coastal freighters.
- 3126B DM7398-00 (370 bhp / 375 mhp / 276 bkW @2600 rpm) - Fast-displacement vessels, patrol boats, charter/commercial craft needing more speed/power.
Cat 3126B Marine 420 bhp / 450 bhp Specs and Curves
| Engine |
CAT 3126B Marine, 420 bhp (313 bkW), DM6177-00 |
CAT 3126B Marine, 450 bhp (336 bkW), DM6181-00 |
| Number of Cylinders |
6 |
6 |
| Displacement |
442 cu in (7.2 L) |
442 cu in (7.2 L) |
| Bore |
4.33 in (110 mm) |
4.33 in (110 mm) |
| Stroke |
5.00 in (127 mm) |
5.00 in (127 mm) |
| Max Power |
420 bhp (313 kW) |
450 bhp (336 kW) |
| Power Measured |
2800 rpm |
2800 rpm |
| Peak Torque |
1040 lb ft (1410 Nm) |
1041 lb ft (1411 Nm) |
| Torque Measured |
2000 rpm |
2000 rpm |
| Governor |
Electronic |
Electronic |
| Flywheel and Housing |
SAE No. 3 (126 teeth) |
SAE No. 3 (126 teeth) |
| Starter |
12 V |
12 V |
| Alternator |
51 amps, 12 V |
51 amps, 12 V, belt driven |
| Rotation (from flywheel end) |
CCW |
CCW |
| Air Cleaner |
Air cleaner with fumes disposal (closed system) |
Air cleaner with fumes disposal (closed system) |
| Fuel Consumption |
23.2 gal/h (87.8 L/h) @2800 rpm |
24.8 gal/h (94.0 L/h) @2800 rpm |
| Aspiration |
Turbocharged Aftercooled |
Turbocharged Aftercooled |
| Exhaust system |
Watercooled exhaust manifold |
Watercooled exhaust manifold and turbocharger |
| Emission Standards |
IMO I emissions level (2000-2010) |
IMO I emissions level (2000-2010) |
- 3126B DM6177-00 (420 bhp / 426 mhp / 313 bkW @2800 rpm) - High-power applications: planing hulls, sport-fishing yachts, sea-going workboats with load.
- 3126B DM6181-00 (450 bhp / 456 mhp / 336 bkW @2800 rpm) - Top-end marine applications: high-speed craft, heavy load-capacity vessels, commercial hulls needing max output.
Service Refill Capacities
| Cat 3126B Marine Engine Version |
Cooling System (engine only) |
Engine Oil Capacity (w/o filter) |
Oil Change Interval |
| 250 bhp (186 bkW) 254 mhp @2400 (DM7370-00) |
10.3 gal (39 L) |
6.6 gal (25 L) |
500 Hours |
| 275 bhp (205 bkW) 279 mhp @2400 (DM7371-00) |
10.3 gal (39 L) |
6.6 gal (25 L) |
500 Hours |
| 315 bhp (235 bkW) 319 mhp @2400 (DM7372-00) |
10.3 gal (39 L) |
6.6 gal (25 L) |
500 Hours |
| 370 bhp (276 bkW) 375 mhp @2600 (DM7398-00) |
10.3 gal (39 L) |
6.6 gal (25 L) |
500 Hours |
| 420 bhp (313 bkW) 426 mhp @2800 (DM6177-00) |
10.3 gal (39 L) |
6.6 gal (25 L) |
200 Hours |
| 450 bhp (336 bkW) 456 mhp @2800 (DM6181-00) |
10.3 gal (39 L) |
6.6 gal (25 L) |
200 Hours |
Recommended oil: Caterpillar DEO 10W30 or 15W40
Weight and Dimensions
| Cat 3126B Marine Engine Version |
Length |
Width |
Height |
Dry Weight |
| 250 bhp (186 bkW) 254 mhp @2400 (DM7370-00) |
62.2 in (1581 mm) |
35.0 in (890 mm) |
36.1 in (917 mm) |
1812 lb (822 kg) |
| 275 bhp (205 bkW) 279 mhp @2400 (DM7371-00) |
62.2 in (1581 mm) |
35.0 in (890 mm) |
36.1 in (917 mm) |
1812 lb (822 kg) |
| 315 bhp (235 bkW) 319 mhp @2400 (DM7372-00) |
62.2 in (1581 mm) |
35.0 in (890 mm) |
36.1 in (917 mm) |
1812 lb (822 kg) |
| 370 bhp (276 bkW) 375 mhp @2600 (DM7398-00) |
62.2 in (1581 mm) |
36.5 in (928 mm) |
36.2 in (920 mm) |
1788 lb (811 kg) |
| 420 bhp (313 bkW) 426 mhp @2800 (DM6177-00) |
62.2 in (1581 mm) |
35.0 in (890 mm) |
36.1 in (917 mm) |
1782 lb (809 kg) |
| 450 bhp (336 bkW) 456 mhp @2800 (DM6181-00) |
62.2 in (1581 mm) |
35.0 in (890 mm) |
36.1 in (917 mm) |
1782 lb (809 kg) |
Cat 3126B Marine Engine Equipment
- Air Inlet System - Sea water aftercooler, 12 V air inlet heater, air cleaner with fumes disposal (closed system).
- Charging System - 12 V, 51 amp alternator (optional 110 amps).
- Cooling System - Gear-driven auxiliary sea water pump, belt-driven centrifugal jacket water pump, auxiliary sea water lines, expansion tank, transmission oil cooler, engine-mounted heat exchanger with removable tube bundle and replaceable copper-nickel tubes.
- Exhaust System - Watercooled exhaust manifold and turbocharger, fumes disposal routed to turbocharger inlet.
- Flywheel and Flywheel Housing - SAE No. 3 (126 teeth).
- Fuel System - Fuel priming pump, fuel filter - RH or LH service.
- Lube System - Crankcase breather; oil filter; oil level gauge, oil filler, oil pan drain - RH or LH service; gear-driven engine oil pump.
- Mounting System - Front mount is not included (Do not use shipping mounts in permanent installation).
- Protection System - Electronic overspeed shutoff.
- Starting System - Rear-facing 12-volt electric starting motor.
- General - Vibration damper and guard, Caterpillar yellow paint, lifting eyes.
From modest 250 bhp installations to high-output 450 bhp drivetrains, the engine covers a wide spectrum of vessel types - from workboats and small commercial craft to larger pleasure craft and light-duty commercial vessels. With refined fuel injection, robust turbocharging and after-cooling, and marine-ready cooling and exhaust infrastructure, the Cat 3126B blends compactness and economy with dependable torque and horsepower delivery. Below is a snapshot of how the 3126B’s marine variants map to different power and performance levels.
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