Cat 3306 Specifications
| Engine Model: Caterpillar 3306 |
| Engine Type: 4-cycle inline 6-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 638 cu.in (10.5 L) |
| Rated Engine Power: 150-300 Hp (112-224 kW) at 2100 rpm |
| Aspiration Type: Naturally aspirated or turbocharged |
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The Caterpillar 3306 is one of the most iconic
and longest-produced diesel engines in Caterpillar’s history. Known for
its reliability, durability, and ability to operate under extreme
working conditions, the 3306 has been widely used in construction,
mining, marine propulsion, industrial equipment, generator sets, pumps,
compressors, and oilfield machinery. Introduced in the 1970s as a
successor to the Caterpillar D333, the 3306 quickly became a favorite
among operators and mechanics due to its straightforward mechanical
design, robust cast-iron construction, and long overhaul life.
Over the decades, the 3306 evolved through multiple variants, including
naturally aspirated, turbocharged, turbo-aftercooled, and electronically
governed models. Many early 3306 engines are still in service today—some
with more than 20,000 operating hours—thanks to their rebuildable
configuration, ease of maintenance, and readily available parts. This
engine’s versatility, strong torque characteristics, and consistent
performance have solidified its reputation as one of Caterpillar’s
greatest mechanical engines.
The Caterpillar 3306 is a four-stroke, water-cooled, inline-six diesel
engine with a fixed cylinder block. Total displacement is 10.5 liters
(638 cubic inches). Bore is 121 mm (4.75 in), and stroke is 152 mm (6.00
in), resulting in a long-stroke design optimized for torque and fuel
efficiency.
Compression ratio depends on the version:
– Naturally aspirated: 16.0:1–17.0:1
– Turbocharged: 15.0:1–16.0:1
– Turbo-aftercooled: 14.0:1–15.5:1
Power output varies significantly depending
on configuration:
– Industrial engines: 150–275 hp (112–205 kW) at 2,000–2,200 rpm
– Construction equipment: 175–300 hp (130–224 kW) at 2,000–2,200 rpm
– Marine propulsion: 150–235 hp (112–175 kW) at 2,000–2,200 rpm
– Generator sets: 150–250 hp (112–186 kW) at 2,000–2,200 rpm
Peak torque typically ranges between 750 and 1,200 Nm (553–885 lb-ft) at
1,200–1,500 rpm. Turbo-aftercooled versions provide the highest torque
output, making them ideal for load-intensive applications such as
earthmoving machinery and drilling rigs. Idle speed is commonly between
650 and 750 rpm. Maximum governed speed ranges from 2,000 to 2,200 rpm
depending on the rating. Firing order is 1-5-3-6-2-4.
The crankshaft is forged steel and fully counterweighted, supported by
seven large main bearings. Pistons are cast or forged aluminum alloy
with reinforced crowns and combustion bowls. The piston ring assembly
includes two compression rings and one oil-control ring. Connecting rods
are forged steel with replaceable bearing inserts. The camshaft is
gear-driven and located in the block.
The 3306 cylinder block is cast iron and built with exceptional strength
for continuous heavy-duty operation. The block features thick cylinder
walls capable of multiple rebores during overhaul. The robust crankcase
design reduces vibrations and supports the heavy rotating assembly.
Large coolant passages surrounding each cylinder promote even
temperature distribution during prolonged high-load operation.
Cylinder bores are parent-block type rather than removable liners;
however, some industrial configurations may include serviceable dry
sleeves depending on region and production year.
The cylinder head is cast iron and features direct-injection combustion
chambers. Each cylinder typically has two valves—one intake and one
exhaust—though some later variants use four valves per cylinder for
improved breathing. The valvetrain uses rocker arms, pushrods, and a
gear-driven camshaft.
Typical valve-lash settings (cold):
– Intake: 0.38–0.43 mm (0.015–0.017 in)
– Exhaust: 0.64–0.69 mm (0.025–0.027 in)
Valve seats are hardened steel for resistance to high thermal loads. The
head gasket uses a reinforced design with fire rings to maintain
combustion sealing under heavy duty cycles.
The Caterpillar 3306 uses a mechanical direct-injection fuel system. A
mechanically driven lift pump pulls fuel through primary and secondary
filters before delivering it to a high-pressure inline fuel injection
pump, commonly a Caterpillar-branded or Bosch mechanical pump.
Key fuel system features:
– Mechanical governor for precise speed control
– High-pressure lines feeding multi-hole injectors
– Injection pressures typically 250–350 bar
– Direct injection into machined piston bowls
Turbocharged and turbo-aftercooled versions may have different injector
flow rates and timing curves to suit higher airflow and boost pressure.
Fuel system maintenance:
– Replace fuel filters every 250–300 hours
– Check and adjust injection timing during major service intervals
– Service injectors every 1,000–1,500 hours
– Drain sediment bowl and water separator as needed.
The lubrication system is a full-pressure wet-sump design with a
high-capacity gear-driven oil pump.
Oil is circulated through:
– Full-flow oil filter
– Bypass oil filter (optional)
– Turbocharger bearings
– Crankshaft and rod bearings
– Camshaft bearings
– Rocker train
Oil capacity depends on configuration: 27–34 liters (28.5–36.0 US
quarts). Recommended oil grades include SAE 15W-40 or 30-weight diesel
engine oil meeting API CF/CH-4 or higher.
Oil pressure:
– 345–550 kPa (50–80 psi) at rated speed
– 140–275 kPa (20–40 psi) at idle.
The cooling system uses a belt- or gear-driven centrifugal water pump
circulating coolant through the block, cylinder head, turbocharger
cooling circuit (if equipped), and aftercooler. The system includes a
thermostat that begins to open at approximately 82°C (180°F) and is
fully open near 95°C (203°F). Cooling-system capacity varies widely with
application: 30–50 liters (32–53 US quarts)
Radiator cap pressure typically falls between 70 and 100 kPa (10–15
psi). Aftercooled models have additional coolant or air-to-air
heat-exchanger requirements.
| Intake and Exhaust Systems |
The intake system depends on application:
– Naturally aspirated models use heavy-duty air filters
– Turbocharged models use single-stage or two-stage turbochargers
– Aftercooled models include air-to-air or water-to-air aftercoolers
The exhaust manifold is heavy cast iron designed to maintain structural
integrity under extreme thermal cycling. Marine and generator models may
use water-cooled exhaust systems.
| Electrical and Starting Systems |
The Caterpillar 3306 uses 12-volt or 24-volt electrical systems
depending on application. Alternator output typically ranges from 35 to
100 amperes. Starter motors are usually 4–7 kW depending on
environmental requirements. Cold-start aids include ether injection or
glow plug systems depending on region.
Electronic versions (3306E) include:
– ECM-controlled fuel delivery
– Real-time monitoring of coolant temperature, oil pressure, boost
pressure
– Diagnostic capabilities and safety shutdown protocols.
Depending on installation, the 3306 may
support:
– Hydraulics (pump drives for construction equipment)
– PTO systems
– Air compressors
– Generator heads
– Marine gearboxes
– Remote cooling systems
– Industrial belt drive systems.
Approximate engine dimensions:
– Length: 1,300–1,500 mm (51.2–59.1 in)
– Width: 850–950 mm (33.5–37.4 in)
– Height: 1,050–1,250 mm (41.3–49.2 in)
Dry weight depends heavily on configuration: 1,100–1,400 kg (2,425–3,086
lb).
– Oil/filter changes: 250–350 hours
– Fuel filters: 250–300 hours
– Air filter: inspect every 50 hours; replace as needed
– Coolant: replace every 2 years
– Valve lash adjustment: every 1,000 hours
– Injector servicing: 1,000–1,500 hours
– Compression test: every 2,000 hours
– Belt inspection: each service cycle
– Turbocharger inspection: every 2,000 hours.
– Cylinder head bolts: 270–310 Nm (199–229 lb-ft)
– Main bearing caps: 400–450 Nm (295–332 lb-ft)
– Connecting-rod bolts: 155–175 Nm (114–129 lb-ft)
– Flywheel bolts: 380–420 Nm (280–310 lb-ft)
– Crankshaft pulley bolt: 450–500 Nm (332–369 lb-ft)
– Oil drain plug: 50–70 Nm (37–52 lb-ft)
– Injector hold-down: 35–45 Nm (26–33 lb-ft).
The Caterpillar 3306 has been used in:
– CAT 966 loaders
– CAT D6 and D7 dozers
– CAT 330-series excavators
– CAT motor graders
– Mining haul trucks
– Drilling rigs and oilfield equipment
– Marine propulsion and auxiliary engines
– Industrial pumps, generators, and compressors.
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