If you live in an area where salt is in the air, like in the beach cities, it’s also important to keep the cars clean and salt-free there as well.
#2: AMBIENT TEMPERATURE AND ENGINE COOLING
If you live in an area where extreme cold is common during the winter, and the car spends a lot of time parked outside, chances are you’re running a lot of anti-freeze in your cooling system. And if you’re not, you should be. Sufficient anti-freeze prevents the engine block from freezing up (totally frozen water expands and will crack your block), and it prevents freezing in the radiator as well—which would otherwise hinder the flow of coolant to your engine and cause it to overheat.
The problem with too much anti-freeze-to-water ratio in the cooling system is that it keeps the car running hotter than necessary. During the Spring, it’s a good time to flush out some of the anti-freeze and replace it with distilled water. Although we all know that 0% anti-freeze and 100% water will freeze at 32F, it’s still a good idea to run at least 10% anti-freeze in the system for its anti-corrosion and increased boiling point properties. If the cooling system is running properly, we shouldn’t be seeing much over 210F—and the more water you use, the cooler it will stay.
So how much anti-freeze should you have in your cooling system, you ask? That depends on the climates you will be driving in. Our nation has a variety of climates in various times of the year. In fact, if you’re driving from Alaska to Death Valley in a given year, you could potentially see up to—and even over—a 200F temperature swing!
While most of our cars may never be driven in this extreme weather, it’s safe to say that a good part of the country will experience anywhere from 15-100F throughout a calendar year. Therefore, we’re going to want to play with some ratios.
There are four things to consider about our coolant when considering anti-freeze: corrosion, cooling, boiling, and freezing.
Corrosion: Anti-freeze comes with corrosion inhibitors that protect the engine over time. The best water to use in a cooling system is distilled water, because tap water contains calcium and magnesium—minerals that leave deposits over time. But prolonged use of distilled water-only is still likely to have some corrosion over time. Hence, we will need at least 10% anti-freeze in the cooling system to corrosion protection. This is what we’ve been doing with Project E46 M3 ever since its new Koyorad radiator install, and the car’s temperature stays around 165F while cruising and rarely hits 180F, and it’s still got a factory thermostat!
The best way to transfer heat from the engine to get cooled by the radiator is straight water. In fact, most racecars run straight water on the track (also because leaking anti-freeze is very slippery on the track, and therefore dangerous). However, as discussed above, regarding corrosion, we’re going to want to run as much distilled water as possible, but also have no corrosion. We mentioned above that we’ll want at least 10% anti-freeze to fight corrosion, so we’re at minimum a 90/10 water-to-anti-freeze mix for maximum cooling over prolonged use so far. But we’re not done yet.
With pure water, our cooling system’s boiling point is 212F. At that temperature, bubbles prevent fluid-to-metal contact, and inhibit the transfer of heat from the cylinder head to the radiator. Pure anti-freeze, on the other hand, has a boiling point of 388F. The problem with running pure anti-freeze is that the car won’t cool as well either.
You may think that running a 50/50 ratio splits the difference and raises the cooling system’s boiling point to the middle—right at 300F, but this is not the case. At 90% anti-freeze, the boiling point already drops to 284F, and by 60% that figure is already at 230F. The increase in anti-freeze from there on out has a more linear effect on the boiling point down to 212F.
While raising the boiling point of our cooling system is good for when it reaches a higher temperature, we are better off not using it as a band-aid for a lack of cooling. Most cars are designed to run between 165-205F coolant temps, with the ideal number being right around the thermostat operation figure—about 185F. If we’re able to keep the cooling system in that temperature, we won’t need to worry about the boiling point as much.
Freezing: Anti-freeze does just as the name implies—prevents freezing in the cooling system. What’s interesting is that, when run by itself, it does indeed have a freezing point of around 10F. However, when mixed with water at a 50/50 ratio, it can withstand temperatures as cold as -35F before freezing.
In most places, including your local gas station, you can buy pre-mixed coolant, which is usually 50/50 anti-freeze and water. While this ratio is an attempt to encompass as much of the nation as possible, it will be provide great anti-freeze and anti-corrosion protection. However, this ratio won’t be optimal in warmer climates for cooling, as discussed earlier.
So now that we understand the different properties to consider, we’re back to asking what our optimal mixture is. To answer that, all we have left is to figure out the coldest climate in which our cars will be driven in. We’ve established above that we need at least 10% anti-freeze for its anti-corrosive properties, so now we can use this chart below to help us find the ideal mixture.
Since the lowest freezing point is achieved at a 40/60 water-to-anti-freeze ratio, there’s no added benefit to using more anti-freeze. Therefore, if you live in an area that will never see less than 26F, your car’s performance will most likely be optimal at a 90/10 ratio year round.
If you live in an area that can see temperatures as low as -10F in the winter, but can also get to 95F in the summer, then you’re better off running a 60/40 ratio. However, if you’re one that may get stuck in traffic with the air conditioner on during the summer months, you may want to make the switch to a 90/10 ratio until winter hits again to get the most out of your car year round.
Make sure to read your vehicle’s owner’s manual to find the coolant system’s capacity so that you can figure out how much anti-freeze to add.
If you're in a situation where a new radiator may be necessary, consider getting an all-aluminum unit, like this Koyorad we put on our Project E46 M3. These won't crack like the factory radiators with plastic end tanks found in numerous cars. They'll last the life of the car and many times also further improve overall engine cooling, especially those with an increased capacity.