Why Not Tap Water? Why Long Life Coolant is Essential for Engine Coolant

While air-cooled engines depend on the wind blowing against the fins, water-cooled engines are effective in preventing overheating in the summer and promoting warm-up in the winter. The key to this is the cooling water in the radiator, but you are not using tap water as it is, are you?　You may think that any liquid that dissipates the heat generated by the engine is fine, but tap water can have unexpected adverse effects and cause serious engine trouble. Riders who only fill their car with water should immediately replace it with long-life coolant.

Tap water corrodes steel and aluminum through repeated heating and cooling.

Water-cooled engines have the advantage of being less likely to overheat even when idling or driving slowly, when cooling by the running wind is not expected, but not just any coolant will do. Tap water, which flows out whenever you turn on the tap, is convenient, but it is not a good choice for the engine.

A reserve tank where coolant flows in and out of the radiator in response to pressure changes inside the cooling system. If the liquid in the tank is cloudy and brown like coffee milk, there is a high probability that the cooling water inside the engine and radiator is tap water.

Coolant used in the cooling system of a water-cooled engine has other roles than just taking heat from the cylinders and cylinder head, which become hot when the mixture burns, and releasing it into the air through the radiator. Tap water under atmospheric pressure boils at 100°C, but the heat received from the cylinders and cylinder heads can reach 100°C or higher, so pressure is applied to the cooling system to raise the boiling point above 100°C. The pressure is not mechanically pressurized, but rather a valve is installed in the radiator cap that does not open until the pressure exceeds atmospheric pressure to keep the pressure high enough to prevent boiling even at temperatures above 100℃. There is also a thermostat that limits the amount of coolant flowing into the radiator during low temperatures to speed warm-up, and a water pump is incorporated to ensure even circulation in the cooling system. In other words, coolant is pumped by the water pump between the engine and the radiator, held back by the thermostat until it reaches the proper temperature, and circulated while being pressurized by the radiator cap. Therefore, it is necessary to use a liquid with appropriate properties in the cooling system. If tap water is used as coolant, several problems can occur. The first is that tap water contains minerals such as calcium and magnesium. These components precipitate as solids due to repeated heating and cooling inside the engine. The same solids precipitate at the tap, but the solids adhere to the radiator and the inner walls of the water jacket inside the engine. The precipitates, known as scale, inhibit heat conduction and narrow the cooling passages, thereby reducing cooling efficiency. Tap water also contains dissolved oxygen and trace amounts of chlorine, which can accelerate metal corrosion. Since the engine cooling system is composed of a combination of different metals such as aluminum, iron, and brass, corrosion can lead to deterioration inside the radiator, damage around the water pump, clogged cooling passages, rust, and other problems.

Corrosion in the cooling system causes water leakage and overheating.

Immediately after the engine is stopped, when the coolant temperature is high, the pressure inside the cooling system is high and hot coolant will gush out when the radiator cap is opened, so it should be opened only after it has cooled sufficiently. The rubber seal on the back side of the cap also has brown rust on it.

This is what you see when you open the water pump drain bolt. When tap water is used, the metal parts inside the engine rust spectacularly. While the use of LLC may be prohibited under limited circumstances such as circuit driving, it is absolutely necessary to use LLC when driving on public roads.

Flush the cooling system by injecting tap water from the top of the radiator. When cold, the thermostat is closed and the amount of water flowing to the water jacket inside the engine is low, so if you want to aggressively wash the water circulation, you can do so with the thermostat removed from the thermostat case.

One potential problem that can occur when tap water is used as coolant is reduced cooling performance due to corrosion and deposits, which should be paid particular attention to. As explained earlier, because different metals are used in the cooling system, electrochemical corrosion, or so-called electrolytic corrosion, can occur due to differences in electrical potential. Tap water is conductive because it contains minerals, which can contribute to this electrolytic corrosion. As the electrolytic corrosion progresses, corrosion can occur inside aluminum cylinder heads and radiators, leading to coolant leakage in the worst case. In addition, the buildup of scale and rust particles in the cooling passages can reduce the radiator's heat exchange efficiency and lead to problems such as wear of the water pump impeller and mechanical seals. In addition, freezing problems cannot be ignored in winter. Water freezes at 0°C and expands in volume when frozen. Since the cooling system is kept airtight by the radiator cap and thermostat, the volume expansion during freezing can cause damage to the radiator, cylinder block, and hoses. Also, although pressurized by the radiator cap, tap water has a lower boiling point than long-life coolant (discussed below), so it tends to boil during high-load operation. When tap water boils in a closed cooling system and generates bubbles called cavitation, it causes a so-called air-biting condition, which lowers circulation efficiency and further raises water temperature. The combination of these phenomena increases the risk of overheating.

Revisiting the role of long-life coolant designed for engine cooling

If clear water comes out of the water pump drain, it can be determined that the inside of the radiator and the inside of the hose from the radiator lower hose to the water pump have been cleaned. However, rust and dirt inside the engine cannot be completely removed when the thermostat is closed.

The contents of the reserve tank are naturally drained as well. Resin reserve tanks do not rust and do not develop holes, but it is not uncommon for steel pipes to corrode and leak on older cars.

You will find that sticking a hose in and flushing with tap water will not remove all the rust when the thermostat is closed. If the car has been neglected for years or even the reserve tank is coffee milk, you want to be prepared and remove all hoses and pipes around the engine to clean it.

Note the rust in the thermostat case and inside the thermostat. Even if tap water is poured in through the radiator cap, as long as the thermostat is closed, tap water will not get inside the engine. Although cooling paths vary from engine to engine, removing the thermostat and cleaning with the thermostat case closed will improve the effectiveness of cleaning the dirt in the water jacket.

To prevent these problems, LLC (long-life coolant) is used; LLC is composed primarily of ethylene glycol and propylene glycol, to which various additives are added. The most important benefit of LLC is its anti-freeze performance. This is evidenced by the fact that LLC has long been called "antifreeze. The glycol component greatly lowers the freezing temperature of water, and at typical concentrations, it will not freeze even at temperatures below 30°C below zero. This performance is impossible with tap water. The boiling point is also higher than that of water, so stable cooling performance can be maintained even under high temperature conditions. What cannot be overlooked is the presence of rust inhibitors and corrosion inhibitors that work to reduce corrosion of aluminum, iron, and other materials. In addition, the water pump is designed to maintain the stability of the entire cooling system by including defoaming agents that prevent foaming of the LLC stirred up by the water pump impeller. In relation to the water pump, it also acts as a lubricant to reduce friction loss in the mechanical seal, thereby extending the service life of the parts. These functionalities make it clear that tap water and LLC are completely different. Furthermore, LLC is not just a non-freezing liquid; it also plays an important role in protecting the cooling system.

Regular replacement of LLC maintains the condition of the cooling system.

However, LLC does not maintain its performance indefinitely, and it gradually deteriorates over time as it is used. The main reason for this is that the additives contained in LLC wear out over time. The inside of an engine is a high-temperature environment, and the coolant is constantly heating and cooling. In this process, rust inhibitors and corrosion inhibitors are gradually degraded and consumed, and their ability to protect metal surfaces decreases. Continued use of degraded LLC can lead to rust and sludge formation inside the radiator and water jacket, resulting in reduced cooling performance. In addition, rust and sludge can cause wear on the mechanical seal of the water pump, leading to coolant leakage. To prevent such problems, it is necessary to replace the coolant every two years for general LLC, and every few years even for long-life coolant. There are two types of LLC: one is a product adjusted to the proper concentration, and the other is a product whose dilution can be arbitrarily changed according to the minimum cold temperature. In either case, it is important to use the proper coolant and replace it regularly to maintain engine cooling performance and ensure long-term reliability.