The hotter the weather gets, the more I realize how much I appreciate liquid-cooled engines. Recent models have longer replacement spans for long-life coolant, reducing the need for maintenance, but this does not mean that you should never replace the coolant. Rather, the longer the period of time for coolant replacement, the more important it is to inspect the cooling system in general.
Insufficient coolant and air contamination can also cause water temperature to rise.
The radiator of the Suzuki RG250 Gamma (1987) uses a down-flow system in which the cooling water flows vertically from the upper tank to the lower tank. In contrast, a radiator with tanks on both sides and cooling water flowing horizontally is called a cross-flow system. The reserve tank is located directly above the radiator. Depending on the model, it may be installed in the side cover or seat rail.
In old cartoons and movies, when a motorcycle had a problem, it was usually depicted as overheating, with a huge plume of white smoke coming out of the engine compartment. What I thought was smoke was steam generated when the pressurized cooling water in the cooling system leaked into the atmosphere for some reason and boiled under atmospheric pressure, but such problems seem to have become rare nowadays.
The JAF, which provides road service for cars and motorcycles, does not rank in the top 10 in terms of reasons for dispatching vehicles for cooling system problems. This can be attributed to the excellent cooling system designed to prevent overheating even when driving slowly in the middle of summer, including the air flow in the engine compartment and cowl.
The life of the coolant itself is also getting longer, and while it used to be common to replace the coolant every 2 years, it is now not uncommon to specify the first replacement every 5 years. It is not uncommon to specify every four years after the second one. If applied to motorcycles and automobiles with vehicle inspections, the first replacement is done at 5 years from new to the 2nd vehicle inspection, and thereafter, 1 replacement is done every 2 vehicle inspections. If you are not interested in maintenance, your awareness of the cooling system itself is diminishing.
However, unlike an air-cooled engine that relies on airflow, the cooling system of a water-cooled engine is not completely maintenance free, as the water pump is constantly circulating cooling water while the engine is operating. Even though the span has been lengthened, regular replacement of the coolant is still necessary, and as mentioned in the previous article, a faulty mechanical seal in the water pump may cause coolant leakage.
Other than that, if air gets into the cooling system due to a decrease in the amount of fluid in the reserve tank, which is connected to the radiator and the hose, the flow of coolant fluid may become poor and the water temperature may rise, just as it does when air entrapment occurs in the brake fluid. Also, if the thermostat, which switches the cooling passage depending on the temperature of the coolant, is not opened, the water temperature will rise too high, and conversely, if it is not closed while still open, the water temperature will not rise easily, causing problems.
In these circumstances, it can be said that, for better or worse, the fact that there are fewer opportunities to pay attention to the timing of coolant replacement and the level of fluid in the reserve tank can lead to panic when problems occur. While the extension of the 2-year replacement to 4 years has certainly reduced the amount of maintenance required, it is important to remember that failure to properly care for the product may result in unexpected repercussions.
- POINT 1: As the span of coolant replacement gets longer, the aintenance awareness of the cooling system in general tends to decrease.
- POINT 2: A decrease in coolant or air contamination can cause the water temperature to rise, and if left unchecked, can lead to engine trouble.
It is important to check not only the radiator itself but also the surrounding parts.
I was relieved to find that the coolant that drained out of the water pump after removing the drain bolts was the correct Long Life Coolant (LLC) and was also clear. When brown tap water mixed with rust comes out, the radiator and all the hoses have to be removed and cleaned.
Rinse the inside of the radiator by sticking a water hose through the radiator inlet. This process will clean the radiator tubes and the path from the lower tank to the water pump, but not the path from the radiator upper hose to the thermostat in the cylinder head area. The reason is that the thermostat is closed when cold, so this is where it comes to a dead end. To flush the area around the cylinder from the thermostat case by plunging a hose of water from the radiator, remove the thermostat from the case, empty it, and then allow the water to flow.
When replacing the coolant, it is generally drained from the drain plug at the bottom of the radiator body in the case of automobiles, or by removing the drain bolt of the water pump in the case of motorcycles. The reason for this is that each of these areas is at its lowest point and can be easily shed naturally by gravity.
However, there are times when simply draining off from the drain bolt is not enough. If the radiator has accumulated scum due to poor management, such as using tap water instead of long-life coolant for the coolant, simply draining the water pump may not be enough to remove the scum from the radiator.
If the motorcycle is only a few years new, this is less likely to happen, but if it is an out-of-print motorcycle from the 1980s or 90s that has passed through multiple owners, you never know how it has been treated along the way. In fact, even though the coolant that drains from the drain bolt part of the water pump is clear, it is not unusual for brown water mixed with sludge and rust to be spewed out when tap water is poured from a hose into the radiator body and pressure is applied.
The same applies to the hoses connecting the radiator to the engine, thermostat housing to the water pump, etc. There have been cases where I grabbed a hose thinking it was hard for a rubber hose and found it coated with rusty water on the inside, or on the other hand, it had deteriorated so much that it was about to burst under pressure. The steel pipes used to connect the hoses to each other are also susceptible to rusting, and if tap water is used instead of long-life coolant, rusting will progress, which can lead to problems with holes in the pipes themselves, not to mention the cooling system in general.
In the case of scooters where there is little difference in height between the radiator and the water pump, it is also effective to send compressor air through the radiator cap into the cooling system to facilitate discharge. However, since the thermostat is closed when cold, The air delivered is effective from the lower hose of the radiator to the water pump, but it is not necessarily perfect to push out the remaining coolant from the thermostat to the upper hose section of the radiator.
If you want to clean the water jacket and upper hose of the cylinder, you will need to remove and install a wide range of parts. However, if you do such a thorough cleaning, you can expect to restore the efficiency of the cooling system.
- POINT 1: When changing the coolant, it is better to clean the radiator, thermostat and other peripheral parts at the same time.
- POINT 2: Sport motorcycles and scooters have different easiness of coolant drainage even with the same cooling system. Always bleed the air after injecting new coolant.
Always bleed the air after injecting new coolant.
There was no turbidity in the discharged coolant, but it was removed to clean the radiator itself. It is good if all the tubes that flow the cooling water up and down are open, but if the tubes are clogged with rust or dirt, the cooling effect will be reduced. In the case of a cross-flow radiator, it is sometimes difficult to notice a problem because the coolant will still circulate even if several tubes from the bottom are completely blocked.
If the reserve tank is dirty, it is difficult to see the amount of the remaining coolant, so it should be cleaned with a fine brush in conjunction with the coolant replacement. If tap water is used for cooling water, it may be discolored with a brown rust.
The removed thermostat was covered with what looked like thin paint chips. When I looked for the cause, it turned out to be the paint film inside the water pump housing. This level of foreign matter is unlikely to affect the function of the thermostat, but it goes without saying that it is better to remove it. I couldn't find this by simply draining the water pump drain. As a result, opening it up was the right thing to do.
In the case of the Suzuki RG250 Gamma introduced here, I expected the cooling path to be quite dirty due to its old age (1987), but fortunately the mileage was less than 5,000 km, and the discharged coolant was clean without any muddiness.
However, I found a bunch of paint chips on the thermostat that seemed to have come off from inside the water pump housing. Fortunately, it was not caught in the valve that controls the flow of coolant, so it was completely closed when cold. However, if a larger foreign object gets caught in the valve, the thermostat will not close, and coolant will circulate even when cold, and it may take longer for the water temperature to rise.
Liquid-cooled engines are not only advantageous in terms of cooling, but they also have the advantage of accelerating warm-up by closing the thermostat and keeping the coolant around the cylinders. During cold weather, it is useful to raise the temperature of the cylinder and combustion chamber to some extent in order to promote fuel atomization, and a thermostatically closed cooling system is also suitable for this purpose. In the past, if you had an engine that was constantly overheating, you could remove the thermostat.
By engine tuning, I've been experiencing heightened levels of heat and heat exhaustion, but as explained earlier, the radiator itself may be clogged, resulting in reduced heat dissipation and overheating, so it may be better to clean the cooling system in general before removing the thermostat.
When injecting new coolant, it is important to bleed the air so that no air remains in the hoses, radiator, thermostat case, etc. As mentioned at the beginning of this article, if air is mixed into the cooling system, it will block the flow of coolant causing the water temperature to rise. The reason for opening the radiator cap when starting immediately after adding coolant is to facilitate air out by opening the cap and allowing the cooling system to reach atmospheric pressure. If the radiator cap is closed while air remains, the air will have no place to escape and will expand as the water temperature rises, blocking the flow of water. Therefore, it is important to drain the bubbles first, even if they are bobbing out of the radiator cap area during warm-up.
Depending on the model, the thermostat case may be equipped with bolts for releasing air. The coolant injected from the radiator flows smoothly from the lower hose to the water pump, but the portion that flows from the upper hose to the thermostat case is a dead end at the thermostat. At this point, by removing the air release bolt from the thermostat case, the coolant flowing vigorously from the upper hose will push out the air in the thermostat case, and warm-up air release will be completed in a short time after the engine is started.
In the middle of summer, when the needle of the water temperature gauge moves a lot, it is a good idea to change the coolant to keep the motorcycle performing well.
- POINT 1: When injecting new coolant, it is important not to leave air accumulation in the hoses or radiator body.
- POINT 2: If the thermostat case leading to the radiator upper hose has an air bleeding function, bleed the air when it is cold.
