Isuzu RZ4F Specifications
| Engine Model: Isuzu RZ4F |
| Engine Type: 4-stroke inline 4-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 133.9 cu.in (2.19 L) |
| Rated Engine Power: 161 Hp (120 kW) at 3600 rpm |
| Fuel System Type: Common Rail Direct Injection |
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The Isuzu RZ4F, marketed under the "MaxForce"
name, is a 2.2-liter, turbocharged, inline four-cylinder diesel engine
representing the latest evolution of Isuzu's "Blue Power" diesel family.
Introduced in late 2024 for the Thai market and rolling out globally
throughout 2025 and 2026, this powerplant was developed as a
higher-capacity successor to the 1.9-liter RZ4E engine. The RZ4F was
engineered to provide increased power and torque for the Isuzu D-MAX
pickup and MU-X SUV while meeting stringent Euro 6e and Euro 7 emission
standards.
The engine operates on a four-stroke, compression-ignition cycle with a
high-pressure common rail direct injection system. A key feature is the
electronically controlled Variable Geometry System (VGS) turbocharger,
which provides faster boost response and improved efficiency across the
rev range.
The RZ4F achieves a 10 percent improvement in fuel efficiency over its
predecessor, with combined cycle consumption figures as low as 6.3 L/100
km in the D-MAX and 8.5 L/100 km in European specifications. A
maintenance-free steel timing chain replaces the belt drive system, and
hydraulic valve lash adjusters eliminate routine valve clearance
adjustments. The engine is paired with a new eight-speed automatic
transmission on most variants, though a six-speed manual remains
available in certain markets.
The Isuzu RZ4F is a four-stroke, compression-ignition, inline
four-cylinder diesel engine. The induction system employs an
electronically controlled Variable Geometry System (VGS) turbocharger
without an aftercooler on standard variants. Total displacement measures
2,194 cc, equivalent to 133.9 cubic inches. The bore dimension is 83.0
mm (3.27 in), and the stroke dimension is 101.5 mm (4.00 in). The
compression ratio is fixed at 15.1:1 or 16.0:1 depending on the specific
market calibration, with Euro-spec engines using the lower ratio for
emission compliance.
Maximum power output reaches 120 kW, equivalent to 163 PS (161 hp), at
an engine speed of 3,600 rpm. Peak torque is 400 Nm, equivalent to 295
lb-ft, delivered across a plateau from 1,600 rpm to 2,400 rpm. A notable
characteristic is the availability of 255 Nm (188 lb-ft) of torque from
just 1,000 rpm, providing exceptional low-speed drivability for towing
and off-road maneuvers. The rated engine speed for continuous operation
is 3,600 rpm, with a governed maximum of 4,500 rpm. Low idle speed is
set between 700 rpm and 750 rpm depending on transmission type and
market calibration.
The cylinder block is constructed from high-strength cast iron using a
closed-deck design for maximum rigidity under high cylinder pressures
generated by the common rail injection system operating at pressures
exceeding 250 MPa (36,000 psi). The block incorporates a
five-main-bearing crankshaft support structure, meaning the crankshaft
rotates on five bearing journals.
This arrangement, with four connecting rod journals positioned between
five main bearings, provides exceptional support for the 101.5 mm long
stroke. The cylinder bores are treated with Isuzu's specialized
"Melt-In" liner technology. This process integrates the liner material
into the aluminum piston sliding surface during casting, creating a
durable, low-friction cylinder wall.
The result is reduced mechanical friction losses contributing to the
engine's improved fuel efficiency. The deep-skirt block design extends
below the crankshaft centerline, enhancing structural rigidity and
reducing noise, vibration, and harshness (NVH) levels. An auxiliary gear
drive at the front of the engine, driven directly from the crankshaft
timing gears, provides mounting points for the high-pressure fuel pump
and water pump. The cylinder block includes provisions for the engine
control unit (ECU) mounting bracket and the hydraulic power steering
pump.
The cylinder head is a cast-aluminum component bolted to the top of the
cylinder block using a single-piece, multi-layer steel (MLS) head
gasket. The cylinder head contains four valves per cylinder, two intake
and two exhaust, for a total of sixteen valves. This DOHC arrangement
uses dual overhead camshafts driven by a maintenance-free steel timing
chain.
The timing chain operates on a system of chain guides and hydraulic
tensioners, eliminating the need for routine timing belt replacement.
The intake camshaft is equipped with a cam phaser for variable valve
timing on certain market variants, optimizing volumetric efficiency
across the engine speed range. The valvetrain incorporates Hydraulic
Valve Lash Adjusters (HVLA). These hydraulic lash adjusters
automatically maintain zero valve clearance throughout the engine's
service life, eliminating manual valve adjustment procedures.
The valves themselves are lightweight hollow-stem designs for reduced
reciprocating mass, allowing the engine to achieve its 3,600 rpm power
peak without valve float. The intake valves measure 29.0 mm (1.14 in) in
diameter, while the exhaust valves measure 25.0 mm (0.98 in). The
pent-roof combustion chamber design centralizes the fuel injector nozzle
for optimum spray pattern and air-fuel mixing. The crossflow cylinder
head positions the intake manifold on the front side of the engine and
the exhaust manifold on the rear side (transverse layout), separating
the hot exhaust passages from the intake charge.
The fuel system employs a high-pressure common rail (HPCR) direct
injection design with full-authority electronic controls. A gear-type
supply pump draws fuel from the tank through a primary water-separating
filter and delivers it at low pressure to the high-pressure pump. The
high-pressure pump, a three-piston radial design driven by the engine
timing gear train, pressurizes fuel to levels exceeding 250 MPa (36,000
psi). This extremely high injection pressure enables finer fuel
atomization, more complete combustion, and reduced particulate
emissions.
The pressurized fuel is delivered to a common rail accumulator mounted
on the top of the engine. The rail stores fuel at constant pressure and
distributes it to solenoid or piezoelectric injectors mounted in the
cylinder head for each cylinder. An engine control unit (ECU) mounted
directly on the engine governs all injection parameters. The ECU
receives input from sensors including crankshaft position, camshaft
position, rail pressure, intake manifold pressure, intake air
temperature, coolant temperature, fuel temperature, and atmospheric
pressure.
The ECU controls each injector independently, varying injection
pressure, timing, duration, and the number of injection events per
cycle. Multiple injection strategies include pilot injections (2-3 small
injections before the main event), the main injection event, and post
injections. The pilot injections reduce combustion noise and nitrogen
oxide (NOx) emissions. The post injections raise exhaust gas temperature
for diesel particulate filter (DPF) regeneration.
The injectors have been upgraded over the RZ4E design to provide finer
atomization and higher flow rates, contributing to the 56 percent
increase in low-end torque. Excess fuel not injected returns to the fuel
tank via a low-pressure return line. The system is calibrated for Euro
6e and Euro 7 emission compliance, incorporating exhaust gas
recirculation (EGR) and a diesel particulate filter (DPF) with selective
catalytic reduction (SCR) in most markets.
The lubrication system is a fully pressurized, wet-sump design using a
variable displacement oil pump. The oil pump is a gear-type unit mounted
on the front timing cover and driven directly by a gear on the
crankshaft. The variable displacement feature adjusts oil flow based on
engine speed and load, reducing parasitic power losses at low loads
while maintaining adequate pressure at high loads. A suction pipe
extends from the pump into the oil sump, drawing oil through a wire-mesh
strainer.
After pressurization, oil passes through a full-flow oil filter mounted
externally on the cylinder block. The filter element is a spin-on,
replaceable canister type with an integral bypass valve. From the
filter, oil travels through internal drillings in the cylinder block to
reach the five main bearings. Drilled passages within the crankshaft
direct oil from the main bearings to the connecting rod bearings.
Excess oil from the bearings is directed upward through vertical
passages to lubricate the camshaft bearings, camshaft lobes, hydraulic
lash adjusters, and the timing chain. The system capacity, including the
oil filter, is 5.9 liters (6.2 US qt) for standard sump configurations.
Operating oil pressure at rated engine speed (3,600 rpm) should register
between 200 kPa and 550 kPa (29 psi and 80 psi).
A pressure relief valve, located near the oil pump outlet, opens at 600
kPa (87 psi) to prevent excessive pressure during cold starts. A
piston-cooling oil jet is directed at the underside of each piston crown
to manage the high thermal loads generated during sustained high-load
operation, such as towing a 3,500 kg trailer.
The cooling system is a pressurized, pump-circulated water system with a
single serpentine belt drive. A centrifugal water pump is driven by the
engine's single serpentine belt, which also drives the alternator and
air conditioning compressor. This simplified auxiliary drive system
reduces weight and maintenance complexity compared to multi-belt
designs. Coolant flows from the lower radiator hose into the water pump,
through the cylinder block water jacket, upward into the cylinder head,
and then out through the upper radiator hose.
A wax-pellet thermostat regulates operating temperature. The thermostat
is located in a housing at the front of the cylinder head. The rated
opening temperature is 82°C (180°F), with full opening at 95°C (203°F).
A bypass circuit allows coolant circulation within the engine block and
head when the thermostat is closed, preventing localized hot spots
during warm-up.
The engine cooling system has been upgraded over the RZ4E design with a
larger radiator and improved airflow through the engine compartment to
support the increased heat rejection of the 2.2-liter displacement. The
total cooling system capacity, engine only (excluding the radiator and
external hoses), is 8.0 liters (8.5 US qt). A belt-driven fan with an
electro-viscous fan clutch provides cooling air flow. The engine is
designed for operation in ambient temperatures up to 50°C (122°F)
without performance deration.
Electrical System: The electrical system is available in 12-volt
configurations for standard applications. A gear-reduction starter motor
engages with the flywheel ring gear. A belt-driven alternator, rated at
150 amperes for most applications, charges the starting battery. The
engine control unit (ECU) requires a stable battery voltage supply for
proper operation.
Air Intake System: Air enters through a dry-type, two-stage air cleaner
with a cyclonic pre-filter. The intake air passes through the Variable
Geometry System (VGS) turbocharger compressor, then through an
air-to-air intercooler (mounted at the front of the vehicle), and
finally into the intake manifold. The VGS turbocharger uses
electronically controlled movable vanes surrounding the turbine wheel to
vary the aspect ratio of the turbine housing. At low engine speeds, the
vanes close, increasing exhaust gas velocity across the turbine for
faster boost response. At high engine speeds, the vanes open, reducing
back pressure for improved volumetric efficiency.
Exhaust System: The exhaust manifold is a 4-2-1 tubular steel design
integrated with the turbocharger mounting flange. Exhaust gases exit
each cylinder into the manifold, pass through the VGS turbocharger
turbine housing, then flow through the exhaust aftertreatment system.
For Euro 6e and Euro 7 compliant variants, the aftertreatment system
includes a diesel oxidation catalyst (DOC), a diesel particulate filter
(DPF), and a selective catalytic reduction (SCR) catalyst with AdBlue
injection. A downstream ammonia slip catalyst (ASC) is fitted on some
variants. The exhaust system includes active noise control through the
ECU's management of multiple injection events.
Timing System: The camshafts are driven by a maintenance-free steel
timing chain. The chain operates on a system of chain guides and two
hydraulic tensioners. One tensioner maintains tension on the drive side
of the chain during normal operation, while a secondary tensioner
controls chain slack during deceleration. The system is designed for the
engine's service life without replacement under normal operating
conditions.
The complete engine assembly, including the turbocharger, common rail
system, alternator, starter, ECU, and exhaust manifold, has an overall
length of 620 mm (24.4 in), a width of 560 mm (22.0 in), and a height of
730 mm (28.7 in). The dry weight, excluding fluids but including all
standard engine-mounted accessories, is 210 kg (463 lb). This represents
a modest weight increase over the RZ4E 1.9-liter engine (195 kg / 430
lb) due to the larger displacement block, longer stroke crankshaft, and
additional aftertreatment components.
Engine oil and filter should be changed every 15,000 km (9,300 miles) or
12 months, whichever occurs first, under normal conditions. Severe duty
intervals (dusty environments, frequent towing, short trips, or extreme
temperatures) require 7,500 km (4,700 miles) or 6-month intervals. Oil
viscosity selection follows API service classification CK-4 or CJ-4.
Recommended viscosities are SAE 0W-20, 5W-30, or 15W-40 depending on
ambient temperature range.
The timing chain requires no scheduled replacement, being a
maintenance-free component. The hydraulic valve lash adjusters require
no adjustment. The fuel filter (primary water separator and secondary
filter) requires replacement every 30,000 km (18,600 miles). The air
cleaner element requires inspection every 15,000 km and replacement when
the restriction indicator shows a vacuum of 25 inches of water (6.2 kPa)
or every 45,000 km (28,000 miles).
The cooling system requires testing of coolant freeze point and
corrosion inhibitor level every 30,000 km. Complete coolant replacement
occurs every 120,000 km (75,000 miles) or five years. The single
serpentine belt requires inspection every 30,000 km and replacement
every 90,000 km (56,000 miles). The diesel particulate filter (DPF)
requires passive regeneration during normal highway driving; forced
regeneration may be required every 500 to 1,000 hours of low-speed
operation. The AdBlue (diesel exhaust fluid) tank requires refilling
every 10,000 km to 15,000 km depending on driving conditions.
Cylinder head bolts are torque-to-yield (TTY) design requiring angle
tightening. First pass torque is 40 Nm (30 lb-ft). Second pass torque is
80 Nm (59 lb-ft). Final pass is an additional 90-degree angle turn.
Connecting rod cap bolts receive a torque of 30 Nm (22 lb-ft) plus a
60-degree angle turn. Main bearing cap bolts are torqued to 50 Nm (37
lb-ft) plus a 90-degree angle turn. Flywheel bolts receive 65 Nm (48
lb-ft) plus a 60-degree angle turn. The crankshaft front pulley bolt is
a single-use TTY bolt torqued to 120 Nm (89 lb-ft) plus a 90-degree
angle turn.
Camshaft bearing cap bolts receive 15 Nm (11 lb-ft). The timing chain
tensioner bolts are torqued to 25 Nm (18 lb-ft). Intake manifold bolts
receive 20 Nm (15 lb-ft). Exhaust manifold nuts are torqued to 30 Nm (22
lb-ft). The common rail mounting bolts are torqued to 25 Nm (18 lb-ft).
The injector clamp bolts receive 12 Nm (9 lb-ft) plus a 90-degree angle
turn. The high-pressure pump mounting bolts are torqued to 25 Nm (18
lb-ft).
The oil filter canister requires tightening to 25 Nm (18 lb-ft) or
three-quarters of a turn after gasket contact. The oil drain plug is
torqued to 40 Nm (30 lb-ft). The water pump mounting bolts receive 15 Nm
(11 lb-ft). The glow plugs are torqued to 15 Nm (11 lb-ft). The starter
motor mounting bolts are torqued to 45 Nm (33 lb-ft). The alternator
mounting bolts receive 25 Nm (18 lb-ft). The ECU mounting bracket bolts
are torqued to 10 Nm (7 lb-ft). The engine mount bracket bolts receive
80 Nm (59 lb-ft).
The Isuzu RZ4F engine is currently offered in two primary vehicle
platforms across global markets. The primary application is the Isuzu
D-MAX one-tonne pickup truck, where the engine launched in Thailand in
November 2024 for the 2025 model year. In the D-MAX, the RZ4F is
available in SX and X-RIDER trim levels in the Australian market, and in
Hi-Lander trim in the Thai market. The second major application is the
Isuzu MU-X seven-seater sport utility vehicle (SUV), where the engine is
available in LS-M, LS-U, and LS-T trim levels.
Both vehicles achieve a 3,500 kg (7,716 lb) braked towing capacity when
equipped with the RZ4F engine, a 500 kg increase over the outgoing
1.9-liter models. The payload capacity varies by body configuration,
with the D-MAX single cab chassis achieving up to 1,350 kg (2,976 lb).
The engine is offered with either a new eight-speed automatic
transmission (the Aisin AWR8 series) or a six-speed manual transmission
depending on market and trim level.
The D-MAX and MU-X equipped with the RZ4F carry a 5-star Euro NCAP or
ANCAP safety rating, incorporating Isuzu's Intelligent Driver Assistance
System (IDAS) with autonomous emergency braking (AEB), adaptive cruise
control, blind spot monitoring, and trailer sway control. The engine has
been confirmed for European markets beginning in 2026, with Euro 6e bis
compliance. The Mazda BT-50, a rebadged version of the Isuzu D-MAX, is
expected to receive the RZ4F engine in future model years. The RZ4F is
distinct from the larger Isuzu 4JJ3-TCX 3.0-liter four-cylinder diesel
engine (140 kW / 450 Nm) which remains available in higher trim levels
in most markets.
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