International DT408 Specifications
| Engine Model: International Harvester DT408 |
| Engine Type: 4-stroke in-line 6-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 408 cu.in (6.7 L) |
| Rated Engine Power: 175-230 Hp (130-172 kW) at 2600 rpm |
| Fuel System Type: Direct injection |
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The International DT408 is a 6.7-liter inline
six-cylinder turbocharged diesel engine produced by Navistar
International during the mid-1990s as a medium-duty powerplant for truck
and bus applications. Designed to fill the gap between the T444E V8 and
the larger DT466 within the International engine family, the DT408
shares mechanical architecture with the legendary DT466 and DT530
variants. The engine employs a four-cycle diesel configuration with
overhead valves and mechanical direct injection, utilizing a Bosch
P-Series inline injection pump for fuel delivery.
Non-intercooled turbocharging provides forced induction across the
operating range. The DT408 features replaceable wet cylinder liners, a
seven-main-bearing crankshaft, and a cast iron block construction that
facilitates in-frame rebuilding without machining. Produced with power
ratings from 175 to 230 horsepower, the engine achieved a B10 life of
approximately 300,000 miles before overhaul, establishing a reputation
for durability in medium-duty vocational applications including school
buses, delivery trucks, and utility vehicles.
Configuration: Inline six-cylinder, longitudinally mounted
Valvetrain: Overhead valve (OHV), 12 valves with 2 valves per cylinder
Displacement: 6.7 liters (408 cu.in)
Bore: 109.2 mm (4.301 in)
Stroke: 118.9 mm (4.680 in)
Compression ratio: 17.5:1
Firing order: 1-5-3-6-2-4
Engine rotation: Clockwise when viewed from the crankshaft pulley end
Aspiration: Turbocharged, non-intercooled in standard factory ratings
Power range: 130-172 kW (175-230 hp) depending on calibration
Peak torque range: 583-732 Nm (430-540 lb-ft) at 1,500 rpm
Engine governed speed: 2,600 rpm
Engine idle speed: 700 rpm
Maximum no-load governed speed: 2,750 rpm
The cylinder block is constructed from cast iron using high-density
green sand casting techniques, providing the foundation for the engine's
heavy-duty durability. The block features a wet liner design with
replaceable cylinder sleeves that seal directly against the block
coolant passages using elastomeric seals at the lower liner bore. This
wet liner construction enables in-frame engine rebuilding without
removing the engine from the chassis or machining the block bores. Seven
main bearings support the crankshaft, with the intermediate bearings
positioned between each cylinder to manage the loads generated by the
long-stroke configuration.
The block incorporates an integral oil gallery running the full length
of the cylinder bank on the right side to supply the main bearings and
connecting rod bearings. Cast-in coolant passages surround each cylinder
liner completely, providing uniform thermal distribution across the
liner height. The block features a deep-skirt design extending below the
crankshaft centerline with reinforced main bearing bulkheads. An
integral front timing gear housing is cast into the block front face.
The cylinder head is manufactured from cast iron using precision casting
techniques, providing thermal stability and wear resistance required for
diesel engine operation. The cross-flow design positions the intake
manifold on the right side and the exhaust manifold on the left side for
conventional chassis installations. Combustion chambers utilize a
pre-chamber design with two valves per cylinder arranged to promote
efficient fuel mixing and combustion.
Valve actuation employs a pushrod and rocker arm system driven by a
camshaft located in the cylinder block. The single camshaft is supported
by seven bearings within the cylinder block and driven by a gear train
from the crankshaft front. Pushrods transfer camshaft motion to the
rocker arms, which pivot on a single shaft mounted in the cylinder head.
Valve lash adjustment requires manual intervention using adjusting
screws on the rocker arms.
Valves: 12 (2 per cylinder)
Intake valve diameter: 44.5 mm (1.75 in)
Exhaust valve diameter: 38.1 mm (1.50 in)
Valve stem diameter: 9.5 mm (0.375 in)
Camshaft drive: Gear-driven from crankshaft, no belt or chain
Valve lash adjustment: Mechanical, hot engine
0The fuel system employs mechanical direct injection with a Bosch
P-Series inline injection pump, designated as the P3000 model. The
injection pump is mounted on the right side of the engine and driven by
a gear from the camshaft. Six individual high-pressure fuel lines
deliver fuel from the pump to the unit injectors or nozzle-and-holder
assemblies mounted in the cylinder head, depending on production
variant. A mechanical governor within the injection pump controls fuel
delivery based on engine speed and load.
Injection pump type: Bosch P3000 inline with mechanical governor
Injector type: Bosch nozzle-and-holder assembly
Injection pressure: 50.0-70.0 MPa (7,250-10,150 psi) at rated speed
Fuel requirement: Diesel fuel meeting ASTM D975 No. 2 specification
Fuel filter: Spin-on canister type with water separator and primer pump
Fuel transfer pump: Mechanical diaphragm pump mounted on injection pump
The lubrication system operates as a fully pressurized wet-sump
configuration utilizing a gear-type oil pump mounted internally within
the front timing gear cover and driven directly by the crankshaft gear
train. The pump incorporates a pressure relief valve calibrated to
maintain system pressure under high-engine-speed conditions. Oil is
drawn from the cast aluminum or stamped steel oil pan through a rigid
pickup tube with mesh strainer.
A full-flow spin-on oil filter is mounted externally on the cylinder
block with convenient service access. A full-flow bypass oil filter may
be installed depending on chassis specification. Oil is distributed
through main galleries cast into the cylinder block, supplying the seven
main bearings, connecting rod bearings, camshaft bearings, rocker shaft,
and piston cooling jets.
Oil pump type: Gear-type with pressure relief valve
Oil pressure at idle (warm): 1.4-2.1 bar (20-30 psi)
Oil pressure at governed speed: 2.8-4.1 bar (40-60 psi)
Oil capacity with filter change: 17.0-19.0 liters (18.0-20.0 US qt)
Oil viscosity specification: 15W-40 meeting API classification CF-4 or
higher
Oil pan construction: Stamped steel or cast aluminum
Cooling system circulation is managed by a belt-driven centrifugal water
pump mounted on the front of the cylinder block. Coolant flows from the
pump into the cylinder block water jacket, circulating around the wet
cylinder liners before passing upward through the cylinder head gasket
into the cylinder head. The thermostat housing is mounted at the
cylinder head front outlet, controlling flow to the radiator based on
coolant temperature. A coolant bypass circuit maintains circulation
through the engine block during warm-up.
Coolant capacity (engine only): 12.1 liters (12.8 US qt)
Thermostat opening temperature: 82-88°C (180-190°F)
Water pump drive: Serpentine accessory belt or direct gear drive
Radiator fan control: Engine-driven fan with thermostatic viscous clutch
Coolant specification: Low-silicate ethylene glycol-based antifreeze
| Intake and Exhaust Systems |
Intake System: A cast iron intake manifold with six individual runners
mounts on the right side of the cylinder head. The turbocharger
compressor outlet connects to the intake manifold through a charge air
pipe. An air-to-air intercooler is not fitted in standard
non-intercooled ratings.
Exhaust System: A single-entry turbocharger mounts on a cast iron
exhaust manifold on the left side of the cylinder head. The manifold
features six individual runners merging into a single collector at the
turbocharger mounting flange. A dry exhaust system routes exhaust gases
from the turbocharger outlet to the vehicle exhaust pipe.
| Electrical and Starting Systems |
Starting System: The electrical system operates at 12 volts. A
heavy-duty electric starting motor is mounted on the right side of the
engine, engaging a ring gear on the flywheel. A gear reduction starter
provides increased cranking torque for cold diesel starts. The
alternator output rating ranges from 100 to 160 amperes depending on
chassis specification.
Starter motor type: Gear reduction, 12-volt
Flywheel ring gear tooth count: 149 teeth
The engine is equipped with a single turbocharger manufactured by
Schwitzer, Holset, or Garrett depending on production period and rating.
The turbocharger utilizes a fixed-geometry turbine housing without
wastegate control for non-intercooled applications.
Turbocharger model: Schwitzer S1 or equivalent
Maximum boost pressure: 0.5-0.7 bar (7-10 psi) at rated speed
Length: 1,080 mm (42.5 in)
Width: 760 mm (29.9 in)
Height: 1,040 mm (40.9 in)
Engine dry weight (complete assembly without fluids): 567 kg (1,250 lb)
Valve clearance inspection interval: 16,000 km (10,000 miles).
Valve clearance adjustment interval: As required based on inspection
findings.
Intake Valve clearance (hot engine, operating temperature): 0.36 mm
(0.014 in).
Exhaust Valve clearance (hot engine, operating temperature): 0.51 mm
(0.020 in).
Engine oil change interval: 16,000 km (10,000 miles) or 250 operating
hours.
Oil filter replacement interval: Every oil change.
Fuel filter replacement interval: 16,000 km (10,000 miles) or as
required.
Coolant replacement interval: 80,000 km (50,000 miles) or 24 months.
Air filter replacement interval: 16,000 km (10,000 miles) under normal
conditions.
Valve lash check: 32,000 km (20,000 mile) intervals.
Injection pump timing check: 160,000 km (100,000 mile) intervals.
Wet cylinder liner protrusion check: At overhaul intervals.
Cylinder head bolts, Step 1: 70 Nm (52 lb-ft)
Cylinder head bolts, Step 2: 140 Nm (103 lb-ft)
Cylinder head bolts, Step 3: 165 Nm (122 lb-ft)
Cylinder head bolts (later production), Step 1: 70 Nm (52 lb-ft)
Cylinder head bolts (later production), Step 2: 150 Nm (111 lb-ft)
Main bearing cap bolts, Step 1: 100 Nm (74 lb-ft)
Main bearing cap bolts, Step 2: 200 Nm (148 lb-ft)
Connecting rod cap bolts, Step 1: 70 Nm (52 lb-ft)
Connecting rod cap bolts, Step 2: 140 Nm (103 lb-ft)
Rocker arm shaft bolts: 27 Nm (20 lb-ft)
Crankshaft vibration damper bolt: 610 Nm (450 lb-ft)
Flywheel housing bolts: 95 Nm (70 lb-ft)
Flywheel bolts: 136 Nm (100 lb-ft)
Intake manifold bolts: 41 Nm (30 lb-ft)
Exhaust manifold nuts: 41 Nm (30 lb-ft)
Valve cover bolts: 20 Nm (15 lb-ft)
Oil pan bolts: 20 Nm (15 lb-ft)
Water pump bolts: 27 Nm (20 lb-ft)
Fuel injection pump mounting nuts: 27 Nm (20 lb-ft)
Injection line nuts: 41 Nm (30 lb-ft)
Engine mount through-bolts: 136 Nm (100 lb-ft)
The International DT408 engine was produced during the mid-1990s and
installed primarily in medium-duty commercial vehicles.
International 3000 Series school buses: The primary application for the
DT408, providing power for type C and type D school bus configurations
with gross vehicle weight ratings from 23,000 to 30,000 lb.
International 4000 Series medium-duty trucks: Utilized in the 4700 and
4800 model trucks for delivery, utility, and stake body configurations
requiring a mid-range diesel powerplant.
International 1652 and 1752 conventional trucks: Installed in these
medium-duty conventional-cab trucks for local delivery and vocational
applications.
AmTran school buses: The DT408 was supplied to AmTran (later IC Bus) for
installation in conventional and forward-engine school bus chassis
during the mid-1990s production period.
Navistar 4000 series chassis for motorhomes: Select motorhome chassis
built on International 4000 series platforms received the DT408 engine
as an alternative to larger DT466 installations in lighter-duty
recreational vehicle applications.
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