Choosing an outboard motor for a PVC boat or a small boat always involves analyzing a variety of parameters, among which the Tohatsu 18 engine size is central. It is the cylinder displacement that is the fundamental characteristic that determines the power potential, torque and, importantly, the efficiency of the power unit. Tohatsu model MFS18 They represent a “golden mean” between light 15-horsepower units and more powerful 20-horsepower versions.
Many owners of water transport mistakenly believe that the power difference between adjacent models is achieved solely by flashing the electronic control unit. Tohatsu engine capacity 18 We're dealing with a unique design of the cylinder block that's different from the older ones, and understanding the physical dimensions of the combustion chamber allows us to better predict the life of the engine and how it behaves under load, and let's look at what the actual casting is hiding under the plastic casing of this popular four-stroke.
It is worth noting that the precise geometric parameters of the piston group directly affect fuel selection and break-in modes. MFS18C2, volume is a constant independent of the carburetor or throttle settings, making this parameter key when calculating theoretical performance and comparing it to competitors such as: Yamaha or Suzuki.
Technical specifications and cylinder litre
The official documentation provided by the manufacturer gives a clear answer to the question of the literage of the power unit. Tohatsu engine capacity 18 This is a figure that is typical of the entire range of two-cylinder four-stroke engines of the manufacturer, where the mechanical part is often unified, and the differences in power are achieved by adjusting the timing phases and the intake system. The figure 362 "cube" is the standard for this power class in the model range of the brand.
The engine design involves two cylinders in a row, which provides excellent balancing and vibration reduction, which is especially important for small craft, and the displacement is equally distributed between the cylinders, which is 181 cm3 per cylinder. Tohatsu MFS18 fitted OHC (top location of camshaft), which allows you to effectively fill the cylinders with a fuel-air mixture even at high speeds.
Why is the exact volume important?
Knowing the exact volume (362 cm3) is essential for the proper selection of spare parts such as gaskets, piston rings and valves, and is critical when squandering cylinders in the event of major repairs, so as not to go beyond the permissible size of repair pistons.
And it's important to emphasize that this volume is a physical power limiter. You can't get more horsepower without changing the compression ratio or adding turbocharging, which is not what we do in aspirated outboard motors. 362 cm This is the foundation on which the whole characteristic of the model is based. For comparison, the more powerful 20-horsepower versions often have an increased litre, which makes them structurally different from 18-horsepower counterparts.
When buying a used engine, always check the markings on the cylinder block. Sometimes unscrupulous sellers give 15-horsepower models for 18-horsepower, although the volume may be identical, but the settings will differ.
Comparison with the model of 20 hp and design differences
The question of how different Tohatsu 18 from Tohatsu 20I'm worried about a lot of potential buyers. engine Unlike some other brands where the difference is only in software, Tohatsu's 18 and 20 hp models often have different piston groups. The 20-power model (MFS20C2) usually has a large displacement of about 395 cubic centimeters, which means that a simple chip tuning won't turn an 18-to-20.
The 33 cubic centimeter difference may seem small, but in the world of low-motorization, it's a significant boost that provides additional thrust at low rpm. The increased stroke of the piston or the cylinder diameter in the 20 hp version allows you to burn more fuel per cycle, generating more energy. So if you're critically important to maximum speed and payload, you should focus on the high-liter model, rather than relying on software to increase the power of the 18-horsepower.
Below is a comparison table showing the differences in the specifications of these two popular models:
| Characterization | Tohatsu MFS18C2 | Tohatsu MFS20C2 |
|---|---|---|
| Workload | 362 cm | 395 cm |
| Number of cylinders | 2 | 2 |
| Maximum power | 18 hp (13.2 kW) | 20 hp (14.7 kW) |
| Maximum revolutions | 5000-6000 rpm | 5000-6000 rpm |
Thus, Tohatsu engine capacity 18 This confirms that the motors were designed as separate units, not as a result of artificially constraining more powerful units, which means predictability of performance and no hidden reserves for boosting without deep interference with the hardware.
Compression degree and combustion efficiency
The displacement is only half the engine efficiency equation, and the second most important variable is compression ratio. MFS18 With a volume of 362 cm3, this parameter is optimized for operation on AI-92 gasoline (or AI-95, which is preferable), the high compression ratio allows you to extract the maximum energy from each cubic centimeter of the fuel-air mixture, providing the declared 18 horsepower.
But be careful: using low-octane fuel in a high-compression engine can cause detonation. Detonation is a devastating process that can damage pistons and valves in minutes of operation under load. The optimum compression ratio for the 362 cm3 volume was chosen by Tohatsu engineers in such a way as to ensure a balance between power and reliability when using standard 92 gasoline, but with a tolerance towards improving fuel quality.
The combustion system in these engines is designed with environmental considerations in mind, and the shape of the combustion chamber and the location of the spark plugs contribute to the complete burnout of the mixture, not only reducing exhaust toxicity, but also preventing the formation of soot on the pistons and valves, which is especially important for two-cylinder engines operating in long-term trolling mode.
☑️ Checking the condition of cylinders at TO
Fuel consumption and economy
Economy is one of the main trump cards of four-stroke engines TohatsuAt 362 cm3 and 18 hp, fuel consumption remains moderate even when in active operation. In trolling mode (about 3000-3500 rpm), the engine consumes minimal gasoline, which allows for long fishing trips without refueling.
At full speed, the flow rate naturally increases, but it remains within reasonable limits thanks to an efficient injection system and precise dosage of the mixture, and for comparison, two-stroke analogues of similar power would consume significantly more oil and gasoline. Tohatsu engine capacity 18 It allows to reach speeds of 30-35 km / h on a standard inflatable boat with a flow rate comparable to a small car.
⚠️ Attention: Real fuel consumption depends not only on engine size, but also on the state of the propeller, the fouling of the lower unit with algae and the weight of the boat. Dirty propeller can increase fuel consumption by 15-20%.
Also worth mentioning is the mode of operation: if you are constantly operating the engine at 80-90% of the power, the flow rate will be close to maximum. To save, it is recommended to select the propeller so that the engine will reach maximum speed only when the boat is fully loaded. Under normal conditions, 70-80% of the gas is enough, where the engine is most efficient.
The four-stroke engine with a volume of 362 cm3 is more economical than the two-stroke analogue by 30-50% due to the absence of fuel losses through the exhaust and an accurate lubrication system.
Reciprocating and oil replacement
The durability of a 362 cm3 engine is directly dependent on the quality of service. The four-stroke design requires the owner to change engine oil regularly. Unlike two-stroke engines, the oil does not burn, but circulates in the system, lubricating rubbing parts, including pistons, crankshaft and camshaft. Replacement intervals are usually 50-100 motor hours or once a season, depending on the intensity of operation.
When replacing oil, it is important to use products with the viscosity recommended by the manufacturer (usually 10W-30 or 10W-40). engine fixed, any damage to the cylinder walls will require expensive cleaning or replacement of the unit.
You also need to monitor the cooling system, because overheating the cylinder head can cause the HBC gasket to deform and cause antifreeze (water) to enter the cylinders, which can cause a hydraulic shock that can destroy the rods and pistons instantly, and regular inspection of the water control hole is a mandatory procedure before each launch.
Frequent questions and troubleshooting
Motor owners. Tohatsu MFS18 They often encounter typical power and volume situations, such as the loss of traction not caused by a problem with the piston group, but by contamination of the carburetor or air supply system. Because the combustion chamber's volume is small, even a small amount of dirt or water in the fuel can disrupt the combustion process.
Another common question is whether you can install a screw with a large pitch. engine capacity 362 cm It allows you to spin the propeller in increments of up to 11 to 12 inches, but in practice it depends on the weight of the boat. If the engine can not spin the propeller to working speeds (5000+), overheating and gas formation will occur, so experiments with screws should be carried out carefully, controlling the tachometer.
⚠️ Warning: Never operate a motor without a flywheel cover installed. This disrupts the cooling system and can cause the cylinders to overheat instantly and jam the pistons.
If you notice a decrease in top speed or an increase in fuel consumption, the first thing you do is check the condition of the candle and the air filter. Often the problem is that the mixture is disturbed, not that the piston group wears off, and you have to start with simple steps before you start measuring the compression.
Can I wash the engine with a kercher?
High pressure washing is acceptable, but only from a distance of at least 50 cm and at an angle. A direct jet under pressure can push the crankshaft coils through, and then the water will enter the crankcase, mixing with the oil, which will lead to an emulsion and the engine will fail.
What is the real engine volume of Tohatsu 18 hp?
The Tohatsu MFS18C2 engine has a displacement of 362 cubic centimeters, a two-cylinder four-stroke engine, where the volume is distributed equally between the cylinders.
Can the Tohatsu 18 power be programmed to 20 hp?
No, you can't. The 18 and 20 hp models have different cylinder volumes (362 cm3 vs. 395 cm3). The mechanical part of the 18-horsepower engine is not designed for loads and performance parameters of the 20-horsepower.
What is the best oil to use in Tohatsu 18?
It is recommended to use semi-synthetic or synthetic oils for four-stroke outboard motors with 10W-30 or 10W-40 viscosity and API class SG, SH, SJ, SL or higher.
Why doesn’t the engine develop full speed?
There may be several reasons: an incorrectly selected screw (too big a step), a contaminated carburetor, poor fuel quality or damage to the exhaust system.