Overheating Causes Oil Temperature Rise! Beware of Trouble with Radiator Fan that are Supposed to Work.

The advantage of a water-cooled engine is that the coolant can maintain the internal temperature of the engine within a certain range. The heat of the coolant is dissipated from the fins when the driving wind hits the radiator, but when the motorcycle is idling or riding at low speed, the cooling fan creates a forced flow of air to cool the motorcycle. If the needle of the water temperature gauge is pointing higher than usual, check not only the condition of the coolant but also the operation of the cooling fan.

Operating status of a motorcycle cooling fan is easier to understand than that of a car.

If you neglect to change the coolant or perform maintenance on the cooling system, coolant may gradually leak out from the hose insert without noticing that the hose band is loose. The band may be tight, but the hose itself may lose its elasticity and leak or smear. So, even if the radiator area is hidden by the cowl and difficult to see, it is a great idea to remove the cowl once in a while to check it.

In contrast to an air-cooled engine, which can only be cooled by the driving wind, a water-cooled engine, with its constantly circulating coolant, is said to be able to perform stably even in summer. While air-cooled engines are still used in motorcycles, water-cooled engines are used in automobiles, and water-cooling is certainly more advantageous in terms of cooling.

However, even though it is water-cooled, the heat received by the coolant from the engine is dissipated into the air through the fins of the radiator, and ultimately, heat transfer does not occur unless the coolant is in contact with air with a temperature difference. For the tubes that the coolant passes through in the radiator, the finely folded, thin aluminum fins are installed in large numbers to provide surface area for heat dissipation.

Increasing the area of the fins will improve the heat dissipation effect, but for more active heat exchange, the fins need to be exposed to airflow. The cooling fan is equipped for this purpose. In the days of front-engine rear-drive (FR) motorcycles, cooling fans were generally driven by a fan belt that split the driving force from the engine crankshaft. Nowadays, the majority of vehicles are front engine front drive (FF), where the engine is placed horizontally in the direction of travel, and radiator fans are commonly used to turn the blades. The cooling fans for water-cooled engines for motorcycles also use radiator fans with motor-driven blades.

The cooling fan is activated when there is insufficient heat dissipation from the fins due to the driving wind or when the engine generates a lot of heat, specifically when idling or slow driving is continued, or when getting off the road from continuous driving on the expressway. In passenger cars, where the driver's seat and engine compartment are far apart, you may not even notice when the cooling fan starts to work, but in motorcycles, the rider and engine are close together, and inevitably the radiator is also close, so you can often feel the radiator fan working. On full cowl motorcycles, many riders may get fed up with the hot air being exhausted from the ducts as soon as the fan starts working.

However, the rising hot air is a sign that the rising water temperature is being cooled. Some models have a fan that keeps turning while the motorcycle is being driven. Some large radiators are available as custom parts for such motorcycles, proving the importance of efficient heat dissipation for water-cooled engines.

When the water temperature becomes abnormally high, the oil temperature also rises, which accelerates the deterioration of the engine oil.

The hoses tightened with hose clamps will have a tendency to crush. The upper hose through which the hot coolant flows can cause the hose to swell due to the heat, making the clamp bite more pronounced. When reusing such hoses, tighten the band around the same part that has bite marks.

If the cooling fan of the radiator does not turn for some reason, or if the radiator does not receive enough airflow, the temperature of the coolant will rise, eventually leading to overheating. When boiling water in a kettle, the water will gradually decrease as steam begins to rise from the kettle on the stove, and if left to boil at 100 degrees Celsius, it will eventually dry up. This is an overheating condition.

Unlike a kettle, the engine's coolant is essentially closed off as a cooling system. By closing it further and increasing the pressure in the path, the boiling point of the coolant is over 100℃. The boiling point of ethylene glycol-based coolant is 120-130℃, depending on the dilution rate of tap water and the pressure applied by the radiator cap. When the temperature reaches higher than that and the coolant boils, it moves into the reservoir tank to relieve the pressure.

If the coolant doesn't do its job of cooling, it's like having a hot water bottle or a pocket warmer. Since the heat generated by the engine includes the heat generated by the engine oil, the oil temperature rises in conjunction with the rise in water temperature. If the oil temperature rises outside of the proper operating temperature range, the viscosity of the oil decreases and the strength of the oil film decreases, increasing the risk of damage to metal parts in contact areas such as around the combustion chamber, which is exposed to high temperatures, and transmission gears, which slide with strong force.

In other words, a rise in water temperature is not just a problem with the radiator or cooling fan, but can also cause damage to the engine itself. When driving slowly in town, the needle of the water temperature gauge shows the high-temperature side, but some owners may think that it's okay because it will cool down as the speed increases. If the cooling fan does not start to turn when the water temperature rises, it is necessary to pursue the cause and take appropriate action.

The two main causes of cooling fan malfunction are the motor itself and the fan switch.

I replaced the radiator with a used one that I won at an online auction, as the caulking part of the left and right tanks had opened slightly due to the impact during the fall. Before installing, flush the inside of the unit with tap water to clean it. The fan switch is located on the top of the tank on the left side.

The fan motor mounted on the back side of the radiator pulls air through the fins from the front side so that it flows in conjunction with the driving wind. When checking the working condition of the fan to be transplanted for radiator replacement, there is less risk of injury if electricity is applied to the fan while it is attached to the radiator rather than to the fan itself.

When applying 12V directly to the fan motor, be careful not to touch or get caught in the fan blades. If the motor seems to be rotating smoothly at full throttle, but there is a strange noise or a grinding noise at the moment when electricity is applied or when stopping after disconnecting the wiring from the battery, the motor itself may be nearing the end of its life.

The fan switch that activates the cooling fan is often attached to the radiator itself, and when the coolant reaches the set temperature, the switch is turned on and the fan motor is energized. Therefore, if the cooling fan does not work, check the fan switch and motor respectively to determine the cause.

The easiest thing to check is the fan motor. You can determine if the motor rotates or not by disconnecting the wires at the connector and applying 12V DC from the battery. In the photo, the fan motor is checked by itself in conjunction with the replacement of the radiator itself, which is leaking some coolant due to cracks in the tank and tube parts, but check it with the fan unit attached to the radiator, as the fan rotating at high speed may cause injury. Even so, you have to be careful not to get your hands or fingers caught in the fan.

If your motorcycle has a cooling fan that rotates even when the main switch is turned off, keep your hands and fingers away from the fan area while the water temperature is high because the fan wiring is directly connected to the battery. If you have to get close to it, you should be careful to disconnect the negative terminal of the battery before working on it.

The function of the fan switch is slightly different for carbureted and fuel-injected motorcycles. For carbureted motorcycles, the fan switch has an on/off structure where the contacts are simply interrupted by the water temperature. Fuel-injected motorcycles, on the other hand, use a water temperature sensor whose resistance changes with temperature, and the change in resistance is input to the ECU and output to the fan relay to activate the motor. Nevertheless, in any case, since continuity and resistance change with changes in water temperature, heat the switch itself in a pot of water, etc., and check if it conducts when it reaches the set temperature.

Incidentally, the thermostat is also an important factor in controlling the temperature of the coolant, but the opening and closing of the thermostat is not directly related to the operation of the cooling fan. When the water temperature is low, the thermostat is closed to promote the warming up of the engine itself, and when the thermostat opens after reaching the opening temperature, the coolant circulates in the radiator, and when the coolant temperature in the radiator reaches the operating temperature of the fan switch, the fan motor is activated.

Therefore, even if the thermostat is replaced with a low-temp type that opens at low temperature because of overheating, the water temperature rise cannot be controlled if the cooling fan does not work due to a defect in the fan switch or fan motor.

As mentioned earlier, the radiator of a motorcycle is located closer to the rider than that of a motorcycle, so it is easier to monitor its working condition. If the needle on the water temperature gauge is pointing to high temperature but the cooling fan is not working, it is recommended to check the function of the fan motor and fan switch.