Cat 3508B Specifications
| Engine Model: Caterpillar 3508B |
| Engine Type: 4-cycle 8-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 2105 cu.in (34.5 L) |
| Rated Engine Power: 912-2011 Hp (680-1500 kW) at 1500 rpm |
| Aspiration Type: Turbocharged and aftercooled |
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The Caterpillar 3508B is a high-performance,
heavy-duty V8 diesel engine engineered for the most demanding
industrial, power-generation, marine, and petroleum applications. As
part of CAT’s 3500B engine family, the 3508B is renowned for its long
overhaul life, exceptional torque output, superior fuel efficiency for
its class, and its ability to operate continuously at high load factors.
It is widely deployed in generator sets, offshore drilling equipment,
mechanical-drive systems, mine haul trucks, marine propulsion, and pump
packages. The engine is valued for its durability, modular
serviceability, and stable operation in harsh environments.
The 3508B integrates advanced turbocharging, precision mechanical or
electronic fuel-injection systems depending on configuration year, a
robust cast-iron block, individual cylinder heads for easy service, and
high-capacity cooling and lubrication systems. Its large displacement
and low-speed torque characteristics enable reliable operation under
continuous heavy load while maintaining long service intervals and low
operating costs relative to its power class.
The Caterpillar 3508B is a four-stroke, water-cooled, V8 diesel engine
with direct injection and turbocharging. Total displacement is
approximately 34.5 liters (2,105 cubic inches). Bore is 170 mm (6.69
inches), and stroke is 190 mm (7.48 inches). The engine uses a 90°
V-configuration optimized for balance and reduced vibration, making it
suitable for stationary and mobile heavy-duty applications.
Compression ratio varies depending on rating, generally between 14.5:1
and 15.5:1. Peak torque output is extremely high, often exceeding:
4,000–6,000 Nm (2,950–4,425 lb-ft).
Power ratings depend on application:
– Generator-drive: 680–1,500 kW (912–2,011 hp) at 1,200–1,800 rpm
– Industrial/mechanical drive: 900–1,500 hp (671–1,119 kW)
– Marine continuous/auxiliary: 800–1,350 hp (596–1,007 kW)
Rated speeds vary by configuration:
– 1,200 rpm
– 1,500 rpm
– 1,800 rpm
The crankshaft is a massive forged-steel component supported by large,
high-capacity main bearings. Pistons are steel-crown aluminum or
all-steel designs depending on configuration, with internal oil-cooling
galleries. Connecting rods are forged steel, capable of withstanding
extreme continuous loads. Camshafts (one per bank) are gear-driven from
the front gear train for long-term timing stability.
The cylinder block is a heavy-duty cast-iron structure with deep
cross-bolted main-bearing saddles, reinforced sidewalls, and
high-rigidity ribbing to support the engine’s continuous-duty power
output. The block houses replaceable wet cylinder liners, allowing the
engine to be fully rebuilt multiple times without machining the parent
bore. Coolant passages fully surround the liners, ensuring uniform
temperature distribution under high load.
Each cylinder has an individual cast-iron head, improving serviceability
and minimizing downtime during maintenance. Heads include
direct-injection combustion chambers with four valves per cylinder—two
intake and two exhaust.
Typical valve-lash (cold):
– Intake: 0.25–0.35 mm (0.010–0.014 in)
– Exhaust: 0.60–0.70 mm (0.024–0.028 in)
Large valves and high-flow porting support efficient combustion at low
engine speeds, improving fuel economy and torque.
Fuel system configurations vary by production year:
Mechanical versions:
– Inline mechanical high-pressure pumps
– Governor control for speed and load
– Multi-element filtration
– Mechanical injection timing
Electronic versions (particularly
B-series):
– Advanced mechanical-electronic unit-injector systems
– Electronic Control Module (ECM) for timing, metering, and protection
– High-pressure fuel actuation for cleaner combustion
Injection pressures:
– Mechanical: 600–900 bar
– Electronic: 1,000–1,300 bar
Fuel-system maintenance:
– Filters every 250–500 hr
– Water-separator draining daily or as needed
– Injector testing every 2,000–3,000 hr
– Pump/ECM inspection during major service intervals.
The lubrication system is a high-capacity, full-pressure wet-sump or
dry-sump system depending on installation. A large gear-driven oil pump
circulates oil through full-flow and optional bypass filtration.
Oil capacity varies widely by configuration: 150–250 liters (40–66
gallons).
Oil pressure:
– Operating: 345–480 kPa (50–70 psi)
– Idle: 120–200 kPa (17–29 psi)
Lubrication targets include main bearings, rod bearings, camshafts,
turbochargers, rocker assemblies, and piston cooling jets.
Cooling uses high-capacity centrifugal
pumps and a dual-circuit cooling layout:
– Jacket-water circuit
– Aftercooler cooling circuit (separate or integrated)
Aftercooling may be seawater-cooled (marine), jacket-water-cooled, or
air-to-water.
Thermostat operation:
– Begins opening: 82°C (180°F)
– Fully open: 95°C (203°F)
Cooling capacity: 250–400 liters (66–105 gallons)
System pressure: 70–120 kPa (10–17 psi).
| Intake and Exhaust Systems |
Turbocharging is standard, with some variants using twin turbochargers
for improved airflow and lower exhaust temperatures.
Air filtration depends on environment:
– Industrial: heavy-duty dual-stage filters
– Marine: water-separating air silencers
– Mining: high-capacity canister-style filtration
Exhaust manifolds are high-temperature cast iron. Marine versions may
use water-cooled manifolds and elbows.
| Electrical and Starting Systems |
Most 3508B engines use a 24-volt electrical system.
Alternators: 50–130 amps
Starter motors: 10–20 kW
Electronic versions include an ECM with diagnostics, event logging, and
engine-protection logic (overheat, overspeed, low oil pressure, fuel
problems).
Depending on application, the 3508B may
drive:
– Marine gearboxes
– Hydraulic pumps
– Air compressors
– Mechanical-drive systems
– Large generator heads
– Compressor packages
– Industrial pumps.
Approximate physical dimensions:
– Length: 2,350–2,650 mm (92–104 in)
– Width: 1,500–1,750 mm (59–69 in)
– Height: 1,700–2,000 mm (67–79 in)
Dry weight: 6,000–6,800 kg (13,228–14,991 lb).
– Oil and filter: 250–500 hours
– Fuel filters: 250–500 hours
– Air filters: inspect every 100 hr
– Coolant: replace every 2–3 years
– Valve adjustment: every 1,500–2,000 hr
– Injector service: every 2,000–3,000 hr
– Turbo inspection: 3,000–5,000 hr
– Compression test: 5,000 hr.
– Cylinder head bolts: 350–450 Nm (258–332 lb-ft)
– Main-bearing caps: 1,000–1,300 Nm (738–959 lb-ft)
– Connecting-rod bolts: 350–450 Nm (258–332 lb-ft)
– Flywheel bolts: 700–900 Nm (517–664 lb-ft)
– Crankshaft pulley bolt: 1,000–1,300 Nm (738–959 lb-ft)
– Oil drain plug: 120–180 Nm (89–133 lb-ft)
– Injector hold-downs: 40–50 Nm (30–37 lb-ft).
The Caterpillar 3508B is widely used in:
– Marine propulsion (tugs, supply vessels, ferries)
– Industrial pump and compressor drives
– Offshore drilling equipment
– Large generator sets (1–2.5 MW)
– Mining haul trucks
– Petroleum pumping units
– Mechanical-drive systems
– Gas compression.
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