[DIY Elementary School]Water-cooled engine main maintenance key points-water tank fine


Compared with the air-cooled engine that cannot be cooled if the engine is not exposed to the wind generated during travel, the characteristic of the water-cooled engine is that even if the motorcycle is stopped, the engine can keep the engine at a proper temperature through the water tank.

Since managing the temperature of the combustion chamber also has a certain effect on controlling exhaust emissions, most motorcycles now use water-cooled engines. In order to maximize the effect of the water-cooled engine, the maintenance and management of the water tank becomes very important.

Therefore, if you see that the liquid inside the tank becomes turbid, you must replace it as soon as possible.

Long-term use will also cause the function of the water tank to decrease


Please wait for the engine and water tank to cool down sufficiently before removing the radiator cap. Some styles of radiators will have a stop screw near the cover. Be sure to check before removing the radiator cover. The deterioration of the radiator cover will also cause the boiling point to drop and liquid leakage.

The cooling principle of a water-cooled engine is to absorb the heat generated by the engine body, and then dissipate heat when passing through the radiator. The water tank is responsible for the heavy responsibility of heat absorption and heat dissipation.

Compared with the air-cooled engine that needs to be cooled by the wind generated during riding, the water tank is circulated through the water pump, and then the radiator is exposed to the wind through the electric fan, and the temperature is easier to manage and control. Therefore, it is very beneficial for high-performance engines that generate a lot of heat and small-displacement cars that often run at high speeds.

Although the performance at high temperatures has attracted much attention, the performance of water-cooled engines at low temperatures is also very important. Although the freezing point of tap water is 0°C, if the water circulating inside the engine freezes at the freezing point, it is very likely that the cooling water circuit will rupture due to volume expansion.

Therefore, the water tank in the water-cooled engine will add liquid that lowers the freezing point, so that the water tank will not freeze at minus 20 degrees Celsius, and even add anti-rust ingredients to prevent the metal parts inside the engine from rusting and allow the water pump to deliver water. A defoamer that does not generate bubbles.

Although the water tank will circulate between the engine and the water tank in accordance with temperature changes, when the temperature rises and the water evaporates, the liquid in the water tank will decrease. If tap water is added to the water tank at this time, it will cause the concentration of the water tank. Decline and the freezing point rise and cause engine problems.

In addition, the longer the use time, the accumulation of dirt inside the radiator body and the cooling circuit will result in a decrease in the cooling effect, so the water tank must be replaced regularly.


・For water-cooled engines, water tank precision is very important.
・The biggest difference between water tank essence and tap water is that it will not freeze even at minus 20 degrees, and it can prevent rust and prevent engine damage even at low temperatures.

You must wait for the engine to cool down before removing the radiator cap

03▲CBR250R is used this time to demonstrate the replacement of water tank essence.

The water pump of CBR250R is on the right side of the crankcase, and there is a radiator downpipe inserted on it, so it is easy to judge. The lowest screw in the water pump cover is the oil pan screw, please use a socket wrench to remove it carefully.


▲If the radiator cover is removed, the water tank will flow out when the oil pan screws are turned. Therefore, please prepare a washbasin or a small basin for spare.

Although the CBR250R’s water tank has a fine capacity of 1.1 liters, because liquid will remain in various parts of the engine, only 0.79 liters are required for replacement.

There are many different standards for the replacement time of the water tank. Some are in the fifth year of buying a new car, and then every four years thereafter, and some models are recommended to be replaced every time the car is inspected. Regardless of the type, the replacement steps are the same.

The most important thing to replace the water tank is that it must be replaced after the engine has cooled down, because as long as it is a liquid, the boiling point will rise when the pressure rises, and when the pressure drops, the boiling point will naturally drop.

Therefore, in order to prevent the water tank from boiling at 100°C, the cooling system in the engine will increase the internal pressure through the radiator cap. If the radiator cap is opened when the engine is not cooled down, it will be caused by the pressure of the cooling system. The difference in atmospheric pressure causes the water tank to boil, which can be sprayed out causing danger. Therefore, when replacing the radiator, make sure that the engine and radiator have become normal temperature, and then remove the oil pan screws near the water pump.

If you don’t know where the oil pan screws of your car are, you can first find the lower drain pipe of the two water pipes connected to the radiator. If you find the drain pipe, you can find where the water pump is.

If there is an air compressor, after removing the oil pan screws and the water tank is all flowing, blow the high-pressure gas at the radiator, so that the water tank remaining in the cooling circuit can be effectively discharged. If scale appears in the drained water tank, the use of detergent can also effectively remove the dirt and rust of the cooling circuit.

After draining the water tank essence in the engine body, it is then replaced with the water tank essence remaining in the water tank. Since the water tank is made of milky white plastic, it is easy to confirm whether there is any liquid remaining. If the water tank is not replaced for a long time, scale may appear inside the water tank. In this case, please use a small brush to remove the scale.


・For different models, the timing of replacing the radiator will also change.
・When replacing the radiator tank, be sure to wait until the engine has cooled down completely before opening the radiator cover.

06▲Because the water tank is connected to the radiator cover with a siphon, when the temperature of the water tank changes, the amount of water inside the water tank will increase or decrease with the volume change.

Exhaust the gas after adding the water tank essence

05▲When the screw of the oil pan of the water pump is locked back, in order to avoid leakage of the water tank, it is necessary to replace it with a brand new gasket. If the gasket is used repeatedly, the torque may increase and the screw will be damaged. Therefore, when you lock the oil pan screw back, please use a brand new gasket, and then lock it with the correct torque value.

The water tank can be divided into a type that can match the desired freezing point, add tap water to dilute the original solution, and a type that is sold in a diluted state. If the former is used, it can be diluted in the correct proportion according to the lowest temperature of the motorcycle’s use area.

The use of a wide-mouth cup is easy to cause liquid leakage, so it is recommended to pour the diluted water tank into an empty PET bottle, and then slowly add it to the radiator.

Since there is still air remaining in the cooling circuit, please start the engine before closing the radiator cover so that the air in the center of the radiator and inside the engine can be exhausted.

After the gas is discharged, the semen level of the water tank will follow, so please add the water tank to make up the reduced amount, and then lock the radiator cover. The above is the process of replacing the water tank essence.

Replacing the water tank will not cause the engine exhaust sound to become quieter or change the riding feeling, but as long as the regular maintenance and replacement before the scale and rust reduce the cooling efficiency, it will definitely reduce unnecessary troubles and increase the car. Service life.

07▲Whether it is the type that needs to be diluted by itself or the type that has been diluted, please use the PET bottle as the container, and then pour the water tank into the radiator.

If you use tap water, not only will it freeze at 0°C, it will also not have the effect of preventing rust. Therefore, it is easy to cause the problem of rust in the steel cooling water pipe.

08▲Even if a large amount of water tank is poured into the radiator during cold start, the water tank will circulate after the engine is started, and the liquid level will drop after the internal gas is discharged. Wait a few minutes for the engine to idle for a few minutes to let the air exhaust, repeat the action of pouring the water tank into the radiator again, and then install the radiator cover.

The deterioration of the water tank is the biggest natural enemy of water-cooled engines

When the clear water tank fluid becomes turbid, it is a sign that the water tank fluid begins to deteriorate. Once the water tank fluid becomes turbid, it may cause the freezing point to rise or the cooling circuit to rust, so be sure to replace the water tank fluid regularly.

※Please wait until the engine has cooled down before performing replacement work.

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Information provided by “Webike magazine”
“Webike Taiwan” editorial department compiled

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