The Caterpillar 3126 Marine Engine, produced from 1995 to 1998, marked Caterpillar’s move into electronically controlled mid-range marine diesels. Built on the foundation of the earlier 3116 but upgraded with HEUI injection, ADEM II electronic management, and improved cooling, the 3126 quickly became a popular choice for both recreational and commercial vessels.
Its combination of lightweight design, good low-end torque, and power ratings up to 420 mhp made it well-suited for planing hulls, sport-fishing boats, patrol craft, and workboats. While early models were known for injector and aftercooler sensitivity, properly maintained 3126 engines remain widely respected for their balance of performance, fuel economy, and serviceability.
Cat 3126 Marine Engine Specs
| Engine | CAT 3126 Marine, 385 hp (390 mhp) | CAT 3126 Marine, 420 hp (426 mhp) |
|---|---|---|
| Number of Cylinders | 6 | 6 |
| Displacement | 439 cu in (7.2 L) | 439 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 | 385 bhp (287 kW) | 420 bhp (313 kW) |
| Power Measured | 2800 rpm | 2800 rpm |
| Peak Torque | 775 lb ft (1051 Nm) | 843 lb ft (1143 Nm) |
| Torque Measured | 2600 rpm | 2400 rpm |
| Compression Ratio | 15.0:1 | 15.0:1 |
| Flywheel and Housing | SAE No. 3, rear-mounted starter | SAE No. 3, rear-mounted starter |
| Starter | 12 V | 12 V |
| Alternator | 51 amps, 12 V, belt driven | 51 amps, 12 V, belt driven |
| Crankcase Ventilation | Walker Airsep Closed Crankcase Ventilation (CCV) System | Walker Airsep Closed Crankcase Ventilation (CCV) System |
| Rotation (from flywheel end) | CCW | CCW |
| Air Cleaner | Air cleaner with fumes disposal (closed system) | Air cleaner with fumes disposal (closed system) |
| Fuel Consumption | 19.5 gal/h (73.7 L/h) @2800 rpm | 21.8 gal/h (82.6 L/h) @2800 rpm |
| Aspiration | Turbocharged Aftercooled | Turbocharged Aftercooled |
| Exhaust system | Watercooled exhaust manifold and turbocharger | Watercooled exhaust manifold and turbocharger |
| Emission Standards | IMO I emissions level (2000-2010) | IMO I emissions level (2000-2010) |
Engine Performance Curves
Planing hull vessels such as pleasure craft, harbor patrol, harbor master, and some fishing and pilot boats.
Cat 3126 Marine: 385 bhp (287 bkW)
Ratings are based on SAE J1228/IS08665 standard conditions of 29.61 in Hg (100 kPa) and 77° F (25° C). These ratings also apply at IS03046/1, D1N6271, and BS5514 conditions of 29.61 in Hg (100 kPa), 81° F (27° C) and 60% relative humidity.
Cat 3126 Marine: 420 bhp (313 bkW)
Fuel rates are based on fuel oil of 35° API [60° F (16° C)] gravity having an LHV of 18 390 Btu/lb (42780 kJ/kg) when used at 85° F (29° C) and weighing 7.001 lbs/gal (838.9 g/L)
Weight and Dimensions
| Dry Weight | 1590 lb (722 kg) |
| Length | 62.8 in (1595 mm) |
| Width | 36.9 in (937 mm) |
| Height | 35.3 in (897 mm) |
Service Refill Capacities
| Cooling System Capacity (engine only) | 7.4 gal (28 L) |
| Engine Oil Capacity (w/o filter) | 6.6 gal (25 L) |
| Engine Oil and Filter Change Interval | 250 Service Hours or 1 Year or Every 2000 US gal (7500 L) of Fuel |
Cat 3126 Marine Engine Equipment
- Air intake - Walker Airsep
- Alternator - belt driven, 12 V, 51 amps
- Cooling System - transmission oil cooler, heat exchanger, engine oil cooler, watercooled exhaust manifold, auxiliary sea water pump, expansion tank, thermostat
- Flywheel and housing - SAE No. 3, rear-mounted starter
- Fuel System - HEUI (Hydraulic Electronic Unit Injection), fuel filter, shutoff solenoid - energized to run, forward routed control cable bracket
- Governor - mechanical
- Lubricating System - oil filter, filler, dipstick
- Service RH and LH - service per top level PAs
- Starting - electric, air i nlet heater
- Support - front
- Torsional vibration damper
- Tachometer drive - magnetic pickup
Note: Caterpillar 3126 marine engine can be operated with air inlet temperatures up to 122° F (50° C) measured at the air cleaner inlet, and fuel temperatures up to (125 ° F (52° C) measured at the fuel filter base. Power rated in accordance with NMMA procedure as crankshaft power. Reduce crankshaft power by 3% for propeller shaft power.
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