What You Need to Know About Engine Coolant

Coolant and AntiFreeze - What it all about?

Engine coolant or antifreeze is one of things that is often miss-understood about your motorcycle. I will try to clear up the confusion on what it does, how it works, and how to maintain your cooling system.

The cooling system of your ride exists to remove excess heat from your engine by circulating a fluid (water) through a heat exchanger (the radiator). The anti-freeze in your coolant serves to protect the water from freezing, to provide some lubrication for the cooling system, and to protect against corrosion of the different parts within the engine. Over time, the coolant does break down and get "worn out", so its cheap insurance to change it every couple of years. I owned a few General Motors cars with leaky head and intake gaskets due to coolant failing to protect the metal parts, so I tend to replace the coolant perhaps more often than necessary. Replacing the coolant is much cheaper than replacing a rotted out head gasket.

As the weather turns colder, its time to start thinking about packing your bike away for the winter. Most rider don't store thier bikes in a heated garage or thier living room, so it might be a good time to check or change your engines coolant to ensure your bike survives the winter. Most coolants call for a 50/50 mix of anti-freeze to water which would give you about -35C protection against freezing. This is fine for your car, but unecessary in your motorcycle (unless you are ice racing) and probably not desireable. I will explain.

Coolant, How Much is Too Much

Water is an amazing substance, it has the highest heat capacity of almost any liquid by weight which means it can carry more heat out of your engine than any other liquid (except ammonia, but that would not be a good thing to put in your engine). So by adding coolant to the water, you actually REDUCE the heat carrying capacity of your cooling system. 

Water has a specific heat capacity of 1 Kcal/kg, while ethyal glycol (antifreeze) is 0.56 1 Kcal/kg, so it has 40% less heat capacity than plain water. By mixing antifreeze with water in a 50/50 mix you have reduced the effectiveness of your cooling system by 15%. That is significant. It could be the difference between boiling over you bike on that monster hill climb or not. See the chart below:

Heat Capacity of Engine Coolant

So if you want to improve the cooling capacity of your cooling system, reduce the amount of coolant you put into the system. I usually run about 25% coolant which gives me around -15C protection and gives me a 8% increase in cooling capacity. I usually bring the bike into the warm house for the winter to get it ready for the upcoming season, but I have left it in the garage all winter, and it has never come close to being frozen (I did check on the coldest days). The garage is usually a bit warmer than the oustside on the coldest days.

Freezing Point

If you bike tends to overheat, you can go as far as to run straight water with some like Water Wetter during the riding season, but make sure you drain it out or add some anti-freeze if you are storing it in a un-heated area. In fact, most road race tracks require that you run only water since an anit-freeze spill can be dangerously slippery to other riders if you have a crash and a coolant leak.

She Can't Take It Any More, She's Gonna Blow!

On the other side of the coolant equation is what tempurature the coolant will boil. Contrary to popular belief, your coolant boiling over is a good thing! Remember, the purpose of coolant is to remove heat from your engine. One of the amazing things about water is whats called the latent heat of vapourization. It takes 1 calorie of energy to raise 1g of water from 99C to 100C, just to the boiling point. In order to boil off 1g of water, that is raise its tempurature above 100C you would need to increadibly, add an additional 540 calories of energy. So when you bikes starts boiling over, it is very efficiently removing HUGE amounts of energy from the engine. Its like a fail-safe device. Instead of cooking your engine, you are cooking the water. Of course if you hadn't put a bigger heat load on the engine or had a more capacity in the cooling system, the engine would not boil over, but when it does, it is actually protecting your engine.

Some companies sell "waterless coolant" which is supposed to prevent boil overs. So if you have been following along, you would quickly realize that this is a very bad thing for two reasons. First water is the best liquid for getting heat out of your engine, it has the highest heat capacity by weight and the purpose of the coolant is to remove heat from your engine. Putting anything else in your cooling system (including anti-freeze) will reduce the cooling capacity.

Second water has a built in insurance policy or fail-safe protection by boiling. If you keeping adding heat to your system and the tempurature keeps rising, it will boil, but when it does, it is saving your engine. Huge amounts of heat are removed from the engine by the process of boiling the water. If the cooling fluid doesn't boil, you can't get this protection.

So What Should I Put in My Radiator?

First off, don't put ordinary tap water in your rad. Use distilled or de-ionized water. Its cheap and contains no disolved minerals that can plug up and corrode your cooling system. You should add something else in addition to water. For a race bike, add water and something like Water Wetter to provide some level of lubrication and corrosion control. Just make sure your don't forget about it in your cold garage, drain it before putting in away for the winter. If your bike has overheating problems, a water/water wetter mix will help keep your engine cooler.

If you want or need some freeze protection, you can be lazy, and spend more money and simply dump a good quality premixed coolant into your bike. This will usually give you a 50/50 coolant/water mix. When you at buying the coolant be careful what you pickup. The premixed stuff is almost the same price as the concentrated stuff for half the amount coolant mixed with water. You can be a little more frugal and smarter and mix your own. I don't recommend a 50/50 coolant water mix, more like a 25/75 mix. This should provide enough freeze protection for your engine, unless you have very cold winters and the bike is left in a cold garage or shed. Then use the standard 50/50 mix for maximum protection.

Bryan Kowalchuk

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