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How To Solve Cooling System Problems And Increase Cooling Efficiency


More than you wanted to know about Liquid Engine Cooling

Liquid cooling is an often overlooked part of an engine's operation. If it's not overheating then everything's good. The problem is that, when trouble does develop, the answers can be elusive.

I'll come right out front by saying that I work at Evans Cooling Systems, Inc. and stand behind the properties of our waterless coolant. I'll tell you about it at the end, but first I'm going to cover some things that you should know if you choose to use a water-based anti-freeze. If you're sick of overheating, you can just skip ahead.


Pressure: A higher pressure will raise the boiling point of a liquid. A lower pressure will lower the boiling point.

Water runs down hill. For us, it's more important to recognize that vapor wants to go up. This is why cooling systems (almost) always flow out of the bottom of the radiator, down to the pump and into the bottom of the engine. Vent lines are placed so that vapor can escape (from the pump, head, or elsewhere) and go up into the radiator. This direction of coolant flow naturally carries vapor up and out of the engine.

Overheating happens when the coolant temperature reaches its failure (boiling) point. Sometimes it is said that when coolant starts spitting out, it's your warning that things are getting too hot. It's not a warning of a failure; it is the failure.

Vapor shielding: As the anti-freeze begins to boil inside the cooling jacket, it forms vapor. Soon the vapor increases from a few bubbles to being a layer along the metal surface. This layer prevents liquid from contacting the metal and the metal is effectively insulated; it is no longer “liquid cooled.” The metal temperature spikes and hot spot detonation, seizure, and other engine damage are the result. Head gasket failure is due to head warping which is the result of uneven temperatures across the head.

System Layout

There are from 6 to 9 basic components depending on the particular layout of the cooling system: radiator(s), cap, overflow tank, hoses, hose clamps, thermostat, cooling jacket (inside engine), pump, and fan. Dirt bikes will lack some of these parts and complex street bikes can have more.

Avoid Boiling the Coolant

The goal of the system is to cool the engine, but that statement is too simple. The goal is to keep the metal temperatures under control and this can only happen if the liquid is in contact with the metal and carries the heat away. It is often recognized that a greater amount of heat is removed through the action of boiling, but this is only true until the bubbles formed grow big and displace the liquid coolant. If the metal is in contact with vapor, not liquid, the metal temperature cannot be controlled. Boiling coolant is to be avoided.

There are two sides to improving the efficiency of your cooling system. One is maintenance and the other the choice of components.


Keep the outside surfaces of the radiator clean. Spray water through the fins from the back to clean out mud and grass. I never use a pressure washer on my bikes. Some teams put a mesh across the front of the radiators in muddy conditions. If the fins get bent, you can spend some time to straighten them out. Every little bit helps improve efficiency.

Check the hoses. Obviously you are looking for cracks or bulges so they can be replaced before a failure. Keep in mind that an older hose can leak through the threads. The hose may look fine, but the coolant can get through the inside layer of rubber and then follow the threads out. Leaks don't always drip to the ground; look for a crusty streak, sometimes at the pump.

Change your anti-freeze every year. After time, the corrosion inhibiting additives fall out of solution and settle out of the coolant; this is the sludge that collects at low points in the system. When this happens, the anti-freeze will continue to cool the engine as it did before, but there is much less corrosion protection. If left like this for too long, the corrosion that forms will insulate the metal surfaces from the coolant and this WILL decrease the cooling efficiency. This is why they suggest using a vinegar rinse to clean the system out.

Diagnosing an overheating engine

Radiator cap: Does the gasket seal? Any rips in it or dirt under it?Is the small disc on the underside free to move? This disc is the return valve that lets coolant back into the radiator from the overflow tank when the engine cools. If the cap doesn't pressurize the system because it doesn't seal, the boiling point of the coolant will be lowered and overheating is the result. A leak elsewhere in the system can also cause a loss of pressure; at operating temperature, you should feel the pressure if you squeeze a hose.

Thermostat: If it is stuck open, it may be hard to warm the engine up on a cold day.If it is stuck closed, the engine will run hot or overheat. You can test it by putting it in water and seeing if/when it opens as you heat it up. Thermostats have different temperature ratings. If it's a “190 thermostat” it should be open at 190F. Racers often remove the thermostat entirely to increase the flow rate of the coolant. Do not remove a bypass type thermostat unless you constrict or block the bypass line. There is a myth out there that if you remove the thermostat, the coolant will flow too quickly to shed the heat through the radiator. The radiator can dissipate heat just fine; in fact, it becomes more efficient with a greater liquid/air temperature difference. The myth originates from a real effect which is based on pressure. The thermostat (or restrictor that may be installed in its place) raises the pressure on the coolant in the engine as the pump pushes against it. This higher pressure raises the boiling point of the coolant inside the engine.

Pump: Obviously, if the pump doesn't pump, you'll overheat. These days pump impellers are likely to be plastic. We've seen manufacturing problems where the impellers separate from the shaft; you could look at this impeller and not see that it's broken, but it would come off in your hand. We've also seen the blades snap off due to cavitation. Cavitation happens when a coolant is close to its boiling point. The “draw” side of the pump naturally has a lower pressure, and this can cause the fluid to vaporize. As the blades smack against this mix of vapor and liquid, they can wear or break. The pump is not designed to pump vapor so this cavitation also slows the coolant flow which will cause the temperature to rise. If the additives in the anti-freeze have fallen out of solution or you've been using straight water without a pump lube, the pump seal can fail leading to a bearing failure. Engine oil that looks creamy is telling you that there's water in it. If it's reddish brown like peanut butter, it's rusty water.

Jetting: A lean fuel/air ratio will cause an engine to run hotter. An aftermarket pipe without proper jetting/fuel injection tuning will flow more air making the engine run leaner. A clogged jet can do the same. Changing things like cams, spark advance, and compression ratio can make an engine run hotter. Ethanol in the fuel will burn leaner. Look for a possible air leak in the boot between the carburetor and head.

Altitude: It's not just that the air is less dense at altitude, but the lowered ambient pressure also has an effect. The radiator cap will pressurize the system to, say, 13 psi *over the atmospheric pressure*. A lower atmospheric pressure will lower the internal system pressure.

You or your friends: If you are riding slowly, there is less airflow to the radiator. If you get stuck or are waiting at a bottleneck, that problem is worse.

Air Pocket: Air trapped in the system can interrupt coolant flow and cause overheating.

Optimizing the System:

Hoses: Silicone hoses are better quality in general and resist heat stress and age cracking. There are silicone hose kits available that eliminate the plastic Y connector. This connector has a smaller inside diameter than the hose, so it restricts the flow; get rid of it if you can. If you go to silicone hoses, spend a little more on the recommended hose clamps so that they don't cut into the silicone. Silicone hoses are more delicate in terms of impacts, so consider a guard in places where a rock may hit it.

Radiators: There are a number of aftermarket radiator companies that make upgraded radiators. Generally they are bigger and/or deeper which adds fluid capacity and surface area to the system, both of which help lower coolant temperature. Whatever radiators you use, make sure they're clean inside and out.

Radiator cap: A higher pressure rated cap will raise the boiling point of the coolant. Race teams sometimes take this to an extreme; I've seen auto racing teams that have an air valve on the cap so they can pressurize it with an air compressor. The FIA limited the allowed pressure in Formula One for safety reasons. I don't recommend raising the pressure more than just a few psi.

Pump: There are some aftermarket pumps available. A better impeller will increase flow and an efficiently designed housing can reduce the flow restriction.

Fan: There are fan kits available now for some dirt bikes; increasing air flow to the radiator will decrease the coolant temperature. Making sure the fan is operating correctly is important. There can be failures of the temperature sensor or fan switch. Some people like to install a manual switch so they can override the automatic operation. If there is a shroud around the fan or ducting that the manufacturer installed, make sure it remains as they intended.

Anti-Freeze: Any coolant with water in it has the same basic properties because those properties are limited by water's characteristics. Water boils at 212F at atmospheric pressure. The boiling point is raised a little when it's mixed 50/50 with glycol, either ethylene glycol or propylene glycol. The big increase in boiling point comes from pressurizing the system. Tap water is terrible stuff to use, but most of the anti-freeze for sale today is pre-mixed with clean water anyway. Many equipment manufacturers have guidelines on the anti-freeze to use such as “no phosphate or silicate based additives”. These additives can be gritty like sand and are bad for pump seals.

Limitations of Water:

Water is corrosive. Anti-freeze manufacturers use a number of different additive packages to fight this property, but they all settle out after time allowing the corrosion to occur. Some additives are bad for seals like silicates. Some additives, like the OAT type(organic acid technology) degrade silicone.

Water conducts electricity. This electrolysis eats metal. You can buy “sacrificial” metal tablets to put in the system that will “absorb” the damage from electrolysis.

Water's boiling point is too close to the operating temperature of the coolant. There is a very narrow safety margin and the anti-freeze will boil in specific locations before the system is observed to be overheating. The area around the exhaust valves is typically quite hot. When the anti-freeze boils here, a vapor layer forms that shields the metal surface from the liquid coolant. The metal temperature then spikes and detonation is the result. The engine will run poorly and lose power as the coolant temperature approaches its failure point. While the system pressure raises the boiling point, it also sets up a situation where a puncture will expel all the coolant. Hot anti-freeze will gush from an opened cap, but not because of the pressure that the cap regulates. When the cap is removed, the pressure drops which drops the boiling point in the system. It is the flash boiling that happens inside the engine that causes the gusher.

Evans Waterless Coolant:

Like I said at the top, I work at Evans, but I'm not just a paid promoter. I started using Evans waterless coolant while road racing in the 1990's when it was still legal for pavement racing. As I became more familiar with its properties, I put it in all my vehicles and started selling it at the track and online. Things grew to the point that my volume was getting noticed by the company. Years later, and here we are with a formula specifically designed for the powersports industry. I'd appreciate it if you'd let me tell you about the product that I believe should be in every performance machine out there. You wouldn't take the back off your watch and pour water in it; it's time to stop pouring water in your engine!

The high boiling point of Evans means that the coolant temperature won't go above its failure point. It operates within the same temperature range as conventional anti-freeze and is able to stay in contact with metal surfaces, even at stressful points like around the exhaust valves. Pump cavitation is avoided, as is electrolysis.

All of Evans' coolant formulas are non-corrosive and last the lifetime of the engine. If I'm rebuilding an engine, I will save the coolant and pour it back in the rebuilt engine. Evans Coolant doesn't freeze; we state that it will flow at -40F, but we have not found a freezing point. After lowering a sample to -60F without freezing, we decided to talk about its pour point like the oil industry does.

Evans Coolant is a patented blend of chemicals, most of which are commonly found in conventional anti-freeze formulas, and additives with no water. It is not a gel and will not turn gooey if anti-freeze is added to it. If something were to happen on the trail and you are forced to add water or anti-freeze, it will simply perform like conventional anti-freeze, no worse. Information on the web about poor cold weather performance of Evans Coolant refers to our oldest formula. The current formulas are approved for all weather conditions and are mandated by Rotax for use in their 900 series aircraft engines.

Evans Coolant has a high boiling point of 375F at atmospheric pressure. While it does not need pressure to raise its boiling point, we do not recommend modifying the system to hold zero pressure. It will expand 7% at operating temperature so you will notice some movement to the expansion tank, but it doesn't build pressure like water does. If you were to open the cap when hot, it shouldn't spurt out. A little might come out, like a tablespoon, but if more does, it is a sign that there is either water present or an air pocket in the system.

The added safety margin of the high boiling point will save the engine when conditions become extreme. Through an unintentional error that cut air flow to the radiator, I saw the coolant temperature on my road race bike go to 297F. The bike was still running alright, so we changed the oil and fixed the cause of the problem. The engine ran fine for all the races that weekend and then all the races at the finals at Daytona.

Evans Powersports Coolant is trusted by race teams around the world. I encourage you to go to our website to learn more and see the interview with Jay Leno or stop by our Facebook page http://www.facebook....300949013264495 for a more personal interaction. When you hear about our Chinese business, you should know that we make the coolant in Pennsylvania and export it into China. Evans China has installed American made waterless coolant into more than 150,000 new passenger cars so far!

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