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Mitsubishi 4G37 Specifications
| Engine Model: Mitsubishi 4G37 |
| Engine Type: 4-cycle inline 4-cylinder SOHC 8-valve liquid-cooled gasoline |
| Total Displacement: 107.1 cu.in (1.75 L) |
| Rated Engine Power: 88-100 Hp (65-74 kW) at 5500 rpm |
| Fuel System Type: Twin-barrel carburetor or multi-point fuel injection |
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| General Technical Data |
The Mitsubishi 4G37 is a 1.8-liter inline four-cylinder gasoline engine that belongs to the long-running Orion family, sharing its design lineage with other Mitsubishi small-displacement powerplants such as the 4G13 and 4G63. Produced from the early 1980s through the mid-1990s, the 4G37 was primarily used in compact sedans and coupes including the Mitsubishi Galant, Lancer, and Mirage. The engine was offered in both carbureted and electronically fuel-injected configurations depending on model year and market.
It was designed to provide an ideal balance of
durability, smooth operation, and fuel economy, while keeping
maintenance straightforward and cost-effective. The 4G37 became
recognized for its reliability and moderate performance, serving as a
dependable daily-use engine during a period when Mitsubishi transitioned
from carburetion to electronic fuel control.
The 4G37 engine was built with a focus on long-term service life,
moderate output, and efficiency. Its single overhead camshaft (SOHC)
valvetrain operates eight valves (two per cylinder), and while simple
compared to later DOHC engines, it provides robust and easily
maintainable performance.
The engine’s cast-iron block ensures strength
and longevity, while its aluminum alloy cylinder head helps reduce
overall weight and improve heat dissipation. The 4G37's straightforward
design made it a favorite among technicians for its accessibility and
mechanical simplicity. Its later EFI variants improved fuel control,
emissions, and responsiveness, bridging the gap between older carbureted
systems and modern multipoint injection engines.
The Mitsubishi 4G37 has a total displacement of 1,755 cc (1.8 liters or
107.1 cubic inches), achieved through a bore of 80.6 mm (3.17 inches)
and a stroke of 86.0 mm (3.38 inches). The long-stroke design provides
strong low-end and midrange torque characteristics, making the engine
suitable for daily driving rather than high-revving performance.
Compression ratios vary depending on
configuration and market: the carbureted version typically features a
ratio of about 8.8:1, while later EFI models employ slightly higher
compression around 9.2:1 to enhance efficiency and power.
The cylinder block is made from durable cast iron with five main
bearings supporting a forged steel crankshaft. The connecting rods are
also forged steel, while the pistons are aluminum alloy with two
compression rings and one oil control ring. The cylinder head is
constructed from aluminum alloy and houses a single overhead camshaft
operating rocker arms and valve stems.
Valve diameters are approximately 42 mm (1.65
inches) for intake and 35 mm (1.38 inches) for exhaust. Valve clearance
is adjusted by screw-and-locknut tappets, requiring periodic inspection.
The firing order is 1-3-4-2, and the crankshaft rotates clockwise when
viewed from the flywheel end.
Power output for the carbureted version typically ranges between 88 and
92 Hp (65 to 68 kW, 87 to 91 bhp) at 5,500 rpm, while torque is
approximately 142 to 145 Nm (105 to 107 lb-ft) at around 3,500 rpm.
Later EFI versions produce between 95 and 100 Hp (70 to 74 kW, 94 to 99
bhp) and up to 150 Nm (111 lb-ft) of torque, improving drivability and
throttle response. Redline is generally around 6,500 rpm with fuel cut
near 6,800 rpm. Idle speed is 750 ± 50 rpm. The standard compression
pressure at 300 rpm is approximately 1,200 kPa (174 psi), with a minimum
limit of 980 kPa (142 psi).
| Fuel System |
The early versions of the 4G37 use a downdraft twin-barrel carburetor
with mechanically and vacuum-operated secondary circuits. Fuel delivery
is handled by a mechanical diaphragm pump driven by the camshaft. The
carburetor incorporates a choke mechanism - manual or automatic -
depending on the vehicle model. The carbureted version uses fuel at low
pressure, around 30 to 40 kPa (4 to 6 psi). Regular inspection and
cleaning of jets and floats are recommended to maintain optimal mixture
control.
Later EFI versions utilize an electronically controlled multi-point fuel
injection (MPI) system managed by an electronic control unit (ECU). The
system includes an electric in-tank fuel pump delivering fuel at
approximately 300 kPa (43 psi) to a common rail feeding four
solenoid-operated injectors. The ECU determines injection timing and
duration based on inputs from sensors such as throttle position,
manifold pressure, intake air temperature, coolant temperature, and
oxygen sensor feedback.
This system provides more precise fuel metering, improving fuel economy and reducing emissions compared to the carbureted setup. Recommended fuel type is unleaded gasoline with an octane rating of at least 91 RON (87 AKI).
| Lubrication System |
The lubrication system is a full-pressure wet-sump type employing a trochoid oil pump driven by the crankshaft. Oil is drawn from the sump through a mesh strainer and delivered to the main gallery feeding crankshaft bearings, connecting rod journals, camshaft bearings, and valve train components. The oil filter is a full-flow, spin-on type located on the block’s right-hand side. Oil pressure under normal operating conditions is approximately 350 kPa (51 psi) at 3,000 rpm and around 100 kPa (15 psi) at idle.
The total oil capacity including the filter is approximately 3.8 liters
(4.0 US quarts, 3.3 Imperial quarts). Mitsubishi recommends high-quality
multigrade engine oil meeting API SG or higher, typically SAE 10W-30 or
10W-40 depending on climate. The oil and filter should be replaced every
10,000 km (6,000 miles) or six months, whichever comes first.
A positive crankcase ventilation (PCV) valve is incorporated into the
rocker cover, returning blow-by gases to the intake system to reduce
emissions and maintain internal cleanliness. The lubrication system also
includes oil jets that spray the underside of the pistons for additional
cooling in some EFI models.
| Cooling System |
The engine employs a liquid cooling system with a belt-driven centrifugal water pump, cross-flow radiator, thermostat, and electric or viscous clutch-driven cooling fan depending on the vehicle model. The thermostat begins to open at 82°C (180°F) and is fully open at 95°C (203°F).
The coolant system operates under pressure of approximately 88 kPa (13 psi) and has a total capacity of around 6.5 liters (6.9 US quarts, 5.7 Imperial quarts). The recommended coolant mixture is 50% ethylene glycol antifreeze and 50% distilled water, providing freeze protection down to –35°C (–31°F). The coolant should be replaced every two years or 40,000 km (25,000 miles).
| Intake and Exhaust Systems |
The induction system differs between versions. Carbureted variants feature a cast aluminum intake manifold designed for even mixture distribution. EFI models employ a tuned long-runner aluminum manifold with a throttle body mounted centrally. The air filter is a dry paper type, replaced every 20,000 km (12,000 miles).
The exhaust manifold is cast iron with four individual runners merging into a single outlet, leading to a catalytic converter and exhaust piping. Some later EFI models include an exhaust gas recirculation (EGR) valve to reduce nitrogen oxide emissions.
| Ignition and Electrical System |
The ignition system on early carbureted engines uses a mechanically advanced distributor driven by the camshaft, featuring contact breaker points or, in later carbureted versions, an electronic ignition module. Timing advance is controlled mechanically by centrifugal weights and vacuum diaphragm. Typical ignition timing at idle is 8° BTDC, adjustable based on fuel quality. EFI engines employ an electronically controlled distributor with integrated ignition module and ECU-governed spark advance.
Spark plugs are typically NGK BP6ES or Denso equivalent, gapped at 1.0 millimeter (0.039 inch). Replacement interval is 20,000 to 30,000 km (12,000 to 18,000 miles). The alternator produces approximately 65 amperes, and the starting motor is rated around 1.0 kilowatt. Electrical system voltage is 12 V DC with negative ground.
| Valve Timing and Drive Mechanism |
The camshaft is driven by a toothed rubber timing belt that also drives the water pump. Belt tension is maintained automatically by a spring-loaded tensioner. The replacement interval for the timing belt is every 100,000 km (60,000 miles). Correct alignment of timing marks on the crankshaft pulley and camshaft sprocket is essential during reassembly.
The belt cover is molded plastic, protecting the drive from contaminants. Valve timing for the 4G37 (SOHC) is approximately as follows: intake opens 8° BTDC, closes 48° ABDC; exhaust opens 52° BBDC, closes 12° ATDC. Valve clearance (cold) is 0.15 mm (0.006 in) for intake and 0.25 mm (0.010 in) for exhaust.
| Dimensions and Weight |
The Mitsubishi 4G37 engine measures approximately 670 mm (26.4 inches) in length, 610 mm (24.0 inches) in width, and 700 mm (27.6 inches) in height. Dry weight is approximately 135 kg (298 lbs) for carbureted versions and 140 kg (309 lbs) for EFI-equipped models. The engine is mounted transversely in front-wheel-drive vehicles and longitudinally in some rear-wheel-drive applications. Rubber-isolated mounts minimize vibration and noise transfer to the chassis.
| Maintenance Data |
Routine maintenance ensures long service life. Engine oil and filter should be replaced every 10,000 km (6,000 miles). Valve clearances are to be inspected and adjusted every 40,000 km (25,000 miles). The air filter should be renewed every 20,000 km (12,000 miles), and spark plugs replaced every 30,000 km (18,000 miles).
The fuel filter is replaced every 40,000 km (25,000 miles). Coolant change interval is every two years or 40,000 km. For EFI engines, the fuel injectors should be inspected or cleaned every 80,000 km (50,000 miles). The timing belt and tensioner must be replaced at 100,000 km (60,000 miles).
| Tightening Torques |
Cylinder head bolts: 40 Nm (30 lb-ft) first stage, 70 Nm (52 lb-ft)
final.
Main bearing cap bolts: 60 Nm (44 lb-ft).
Connecting rod bolts: 40 Nm (30 lb-ft) plus 90 degrees.
Camshaft bearing cap bolts: 13 Nm (10 lb-ft).
Crankshaft pulley bolt: 160 Nm (118 lb-ft).
Flywheel bolts: 85 Nm (63 lb-ft).
Intake manifold bolts: 25 Nm (18 lb-ft).
Exhaust manifold nuts: 35 Nm (26 lb-ft).
Spark plugs: 18 Nm (13 lb-ft).
Oil drain plug: 40 Nm (30 lb-ft).
Valve cover bolts: 9 Nm (7 lb-ft).
| Vehicle Applications |
The Mitsubishi 4G37 was widely used in a variety of compact and mid-size
vehicles between the early 1980s and mid-1990s.
Key applications include:
– Mitsubishi Galant (E11 to E33 series, 1983–1992)
– Mitsubishi Lancer (A170, A180 series, 1983–1988)
– Mitsubishi Mirage and Colt (1983–1991)
– Hyundai Stella and early Elantra (as licensed versions of the 4G37)
– Dodge Colt and Plymouth Laser (some export markets)
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