In the 10+ years of track experience we have had, we’ve made a lot of mistakes and learned a lot of lessons. Hopefully, the lessons in this article will make life easier for you. First things first, I may interchange the words water and coolant, don’t get mad at me. In practice, you use water and coolant differently for different applications. Assuming you’re trying to maximize engine cooling, water cools more efficiently than coolant. It is also safer to use on a racetrack as it is less slippery in the case of spills. That being said, water will freeze at 32 F (0 C), so don’t use pure water if there’s any chance of being near freezing temps. Additionally, pure water can lead to corrosion, weird particulates and sludge, when used for long periods of time without some sort of conditioner. If you have a dual-purpose street/track car, the basic info below applies to equally to coolant as well. Enjoy! The biggest lesson, pressure management We’re going to start very basic, so bear with me, but rule number one: as water pressure increases, so does the boiling point. This is perhaps the most important thing to know about your cooling system. Why? Coolant needs to be in contact with the inner surfaces of your engine and radiator to cool. If the coolant boils, it’s no longer in contact with surfaces and then thermal failures can occur very quickly. Engines normally operate in a coolant temperature range of roughly 180 °F - 200 °F (82 °C - 93 °C) window. In standard atmospheric conditions, water boils at 212 °F (100 °C). You can see, without additional pressure, the engine is very close to reaching the standard boiling point of water. If you’re at the track, with extended high throttle conditions, the engine will produce additional heat. Without additional pressure, that heat will start boiling your coolant easily. Next thing you know, you have a broken engine. Check the number on your radiator cap to determine maximum pressure before the cap opens. 1.1 is in bar, a metric unit of pressure, in this case. Luckily, vehicle designers took this into account and came up with a pressurized cooling system! If you notice, there are the digits, 1.1, on your Fast and Furious Honda Civic radiator cap. This stands for 1.1 bar of pressure (about 16 psig). Side note, this number isn’t taking into account standard atmospheric pressure, which can be confusing. That 1.1 bar of pressure, in addition to the aforementioned normal atmospheric pressure, magically increases the water’s boiling point to about 250 °F (121 °C). This gives you much more headroom for heat to enter the coolant, without boiling. Thanks science nerds for figuring that one out! How a radiator cap works. Courtesy of http://www.sw-em.com/. You may be wondering, how does the cap increase pressure and boiling point? Well, it doesn’t. The cap acts as a two-way valve. Depending on coolant system conditions, it will hold pressure, open to relieve pressure or open the other way to relieve vacuum. When the engine warms up, the water expands, increasing pressure. In the case of the 1.1 bar Civic radiator cap, it will keep the system pressurized until 1.1 bar (16 psig). After that, the radiator cap will overflow coolant into an unpressurized reservoir tank. Once the system cools back down and compresses, it’s possible that the cooling system would be under vacuum. In these conditions, the radiator cap will allow coolant to flow back from the reservoir, refilling the system. Neato! It should be noted, just because your radiator cap says 1.1 bar, your system may not fully reach that pressure. This means, you might not exactly have a 250 °F boiling point in practice. Additionally, any air in your system hurts the pressure increase as well, lowering the max boiling point. REALLY FREAKING IMPORTANT NOTE ABOUT CHECKING COOLANT LEVELS The last little paragraph above is critically important for track day drivers. Why? At the track, we can have cooling system issues, causing us to lose coolant while out in a session. This will then cause us to check coolant levels. While not recommended, many of us relieve the pressure of a warm system by slowly removing the radiator cap. Then we top off the coolant/water and head back out. DON’T DO THIS. We had to insert the stereotypical overheating radiator image somewhere. If your car is doing this, don't refill the coolant and go right back on track. The cooling system relies on temperature differential to increase system pressure to a point where the coolant won’t boil. If you release the pressure at a high temperature and go back out before the system fully cools, guess what? Your cooling system’s boiling point is dramatically lower, making your car more likely to overheat. While it is critically important to replace any lost coolant during a session, it is also critically important to keep the cooling system in the proper pressure window. Don’t open the system at higher temps, unless you can re-pressurize! See the MotoIQ article below for Dave Coleman’s tips and tricks to get around this problem. Bernoulli's principle. This is important for your cooling system and aerodynamics. Learn it, know it, be it! Now that we have a basic understanding of cooling system pressure, it is important to understand that the cooling system has different pressures in different areas. Bernoulli's principle shows us that flow will indicate pressure levels. Areas of high flow, such as the return line from the radiator to the water pump, will have relatively lower pressures. Areas of low flow, such as in front of the thermostat or convoluted areas of the engine block and cylinder head, will have relatively high pressures. Then to complicate things further, heat effects pressure. With higher temperatures yielding higher surface pressures (unless the coolant is boiling). Why is this important? This means each area has different, localized boiling points. Most importantly for this lesson, the radiator cap may be … Continue reading How to make your street car’s cooling system race and track-day ready.
