Tohatsu M70C Specifications
| Engine Model: Tohatsu M70C |
| Engine Type: 2-stroke 3-cylinder gasoline outboard engine |
| Total Displacement: 57.2 cu.in (938 cc) |
| Rated Engine Power: 70 Hp (52 kW) at 5500 rpm |
| Fuel System: Carburetor |
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The Tohatsu M70C is a robust and
well-engineered carbureted two-stroke outboard, noted for outperforming
its de-rated 60hp counterpart. Its key strength lies in its robust lower
unit, borrowed from the 90hp model, and a deep gear ratio that
translates into superior thrust for planing boats under load. It
features a voltage-regulated 11-amp alternator, a significant advantage
over some competitors with lower-output systems, ensuring ample power
for fish finders and GPS units.
The engine utilizes an electric choke system, which is inherently
reliable and easy to service, though cold starts require a coordinated
use of the fast idle lever and choke. While based on technology from the
late 1990s, it remains a popular choice for its simplicity, strong
acceleration, and good value, especially for saltwater anglers with
smaller boats.
Engine Model: Tohatsu M70C EPTO, M70C MFG
Engine Type: 2-Stroke.
Number of Cylinders: 3.
Bore x Stroke: 74 mm x 72.7 mm (2.91 in x 2.86 in).
Piston Displacement: 938 cc (57.23 cu in).
Power Output: 52 kW (70 HP).
Full Throttle Operating Range: 5150-5850 r/min.
Idle Speed in Neutral Gear: 900 r/min.
Minimum Trolling Speed in Forward Gear: 750 r/min.
Exhaust System: Through-hub exhaust.
Cooling System: Forced water cooling with thermostat control.
Starting System: Manual (MFG model) / Electric starter motor (EPTO
model).
Ignition System: Flywheel magneto CDI (Capacitor Discharge Ignition)
with mechanical timing advance.
Spark Plugs: NGK B8HS-10 or BR8HS-10 (Spark plug gap: 0.9-1.0 mm /
0.035-0.039 in).
Alternator: 12V, 130W (12V, 11A).
Trim System: Manual tilt (MFG model) / Power trim and tilt (EPTO model).
Trim Positions (MFG): 5.
Fuel: Unleaded Regular Gasoline with an anti-knock index (R+M/2) of 87
or higher, or a Research Octane Number (RON) of 91 or higher.
Fuel Tank Capacity: 25 liters (6.6 US gal).
Engine Oil: Genuine motor oil or TCW-III certified oil.
Fuel-to-Engine Oil Mixing Ratio: 50:1 (for manual mix models) /
Automixing system variable ratio (50:1 - 120:1). Gear Oil: Genuine Gear
Oil or API GL5, SAE 80-90.
Gear Oil Capacity: 0.9 liters (30.4 fl oz).
Gear Reduction Ratio: 2.33 (12:28).
The M70C features a loop-charged, three-cylinder powerhead, a design
that promotes efficient scavenging of exhaust gases and delivery of the
fuel-air mixture for improved combustion and fuel economy compared to
older cross-flow designs.
The combustion chambers utilize Tohatsu's "dual swirl" design, a feature
that helps the carbureted engine comply with US EPA exhaust emission
regulations by promoting more complete fuel burning. The ignition system
is a CDI unit with mechanical timing advance.
The fuel system is carbureted, with one carburetor feeding each cylinder
for precise fuel metering. It runs on standard 87-octane unleaded
gasoline. The system includes a separate, easily accessible bowl-type
fuel filter for routine maintenance.
A standard 25-liter external fuel tank is provided. For cold starts, the
engine employs an electric choke system rather than a primer bulb, which
is noted for its reliability and ease of service despite requiring a
specific starting procedure.
The M70C is equipped with Tohatsu's automixing oil injection system as
standard equipment. Oil is injected directly at the fuel pump, ensuring
that the carburetor throttle butterflies and other components receive
proper lubrication. This design avoids the use of separate,
small-diameter oil lines to each cylinder, which can be prone to
clogging from oil gelling.
The under-cowl engine oil tank has a capacity of 2.6 liters. The system
automatically varies the fuel-to-oil ratio between 50:1 and 120:1
depending on engine load and speed. During the 10-hour break-in period,
a 50:1 pre-mix in the fuel tank is recommended in addition to the oil
injection system.
Cooling is managed by a forced water system, thermostatically controlled
to maintain consistent engine operating temperatures for efficiency and
longevity. A water pump, featuring a durable stainless steel housing,
draws water through intakes in the gearcase and circulates it through
the engine. The system includes an overheat warning system that provides
an audible alarm if the engine approaches a critical temperature.
| Mid Section and Lower Unit |
A defining feature of the M70C is its mid section and lower unit, which
are shared with the larger Tohatsu M90A model. This robust gearcase
houses a forward-neutral-reverse gearbox with a deep gear reduction
ratio of 2.33:1, which is highly effective at converting engine torque
into propeller thrust for planing heavier boat loads.
The recommended gear oil is a genuine Tohatsu oil or an API GL5 grade,
SAE 80-90, with a total capacity of 0.9 liters (30.4 fl oz). The lower
unit is fitted with a trim tab that also functions as a sacrificial
anode for corrosion protection.
The M70C is offered in two primary configurations: the M70C MFG with a
manual trim and tilt system, and the M70C EPTO with a power trim and
tilt system. The manual system utilizes mechanical tilt locks and a
shallow water drive option.
The power trim and tilt system, available on the EPTO model, uses
electric hydraulic pumps to allow the operator to adjust the motor's
angle for optimal performance and to fully raise the motor for
trailering or beaching. The manual release valve provides a backup for
lowering the motor in case of power failure.
The propeller is selected based on boat and load to allow the engine to
operate within its WOT range of 5150-5850 r/min. The M70C uses a
propeller with a spline drive. The recommended propeller selection range
is from 11 to 21 inches of pitch.
A demonstration boat performed well with a 15-inch pitch aluminum
propeller. When installing or removing the propeller, it is critical to
use a block of wood between the blade and the anti-ventilation plate to
hold it, and to always use a new split pin on the propeller nut.
Overall Length (EPTO model): 720 mm (28.3 in)
Overall Length (MFG model): 1280 mm (50.4 in)
Overall Width: 360 mm (14.2 in)
Overall Height (Long Shaft EPTO model): 1415 mm (55.7 in)
Overall Height (Long Shaft MFG model): 1455 mm (57.3 in)
Overall Height (Ultra Long Shaft EPTO model): 1542 mm (60.7 in)
Overall Height (Ultra Long Shaft MFG model): 1582 mm (62.3 in)
Transom Height (Long Shaft model): 517 mm (20.4 in)
Transom Height (Ultra Long Shaft model): 644 mm (25.4 in)
Weight (Long Shaft EPTO model): 115 kg (254 lb)
Weight (Long Shaft MFG model): 105.5 kg (233 lb)
Weight (Ultra Long Shaft EPTO model): 117.5 kg (259 lb)
Weight (Ultra Long Shaft MFG model): 108 kg (238 lb)
First 10 Hours / 1 Month: Initial dealer inspection. Every 50 Hours / 3
Months: Check and clean fuel and oil filters. Inspect spark plugs, clean
or replace as needed, and adjust gap to 0.9-1.0 mm (0.035-0.039 in).
Check and re-tighten all accessible bolts and nuts. Apply grease to all
sliding and rotating parts and grease nipples.
Every 100 Hours / 6 Months: Change gear oil, inspecting for water or
metal particles. Have a dealer check carburetor adjustment and ignition
timing. Inspect the water pump impeller for wear.
Annually / Every 100 Hours: Replace the water pump impeller regardless
of apparent condition. General: Check anodes for corrosion and replace
if significantly eroded. Flush the cooling system with fresh water after
each use in salt or polluted water using the flushing attachment on the
gear case.
Cylinder Head Bolts: 25-29 Nm
Propeller Nut: 25-35 Nm
Gear Housing Bolts: 20-25 Nm
Spark Plugs: 20-27 Nm (14.8-19.9 lb-ft)
The Tohatsu M70C is designed for a wide variety of small to medium-sized
boats, where its power-to-weight ratio and robust lower unit are
advantageous. Ideal applications include: Fishing Boats: A popular
choice for aluminum tiller-steered boats, center consoles, and side
console fishing boats up to five meters.
Runabouts: Provides strong performance for small fiberglass runabouts
and bowriders. Utility Boats: Well-suited for jon boats, skiffs, and
other light commercial or recreational utility craft.
Pontoon Boats: Suitable for powering smaller pontoon boats.
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