The human body doesn't like to overheat and engine's aren't much different. Temperature can determine just how much power an engine can make, how efficiently it will run, and whether or not it will hold together. Excessive cooling system temperatures can cause hoses to burst, headgaskets to blow and even cylinder heads and engine blocks to warp; the fact that they'll lose significant amounts of power goes without saying. It's not good. That's why it's important to keep water temperatures under control. Common cool-down methods include larger frontal area and/or thicker aluminum radiators, which have the ability to dissipate more heat quickly, but can also be fairly expensive. Sometimes adding a larger or secondary cooling fan will help alleviate low-speed or idling cooling issues. But even adding another fan or a larger one will cost you a bit of cash and may cause problems when it comes time to fitting it in place. Either way, if your engine is overheating, it has to be taken care of otherwise you'll end up with expensive problems that make the price of an aluminum radiator seem more on par with the amount of change you've got under your couch cushion.

The modern day gasoline engine isn't all that efficient, at least not as much as we'd like it to be. Fuel energy that could potentially be used to produce additional power is constantly lost through the cooling system. The process is called heat rejection, and if it didn't take place, thermal breakdown of the pistons, cylinders and cylinder head could occur. Call it a tradeoff. Cooling is also important when it comes to the ignition process and the combustion chamber. As combustion chamber temperatures increase, higher octanes of fuel or retarded spark timing are needed. The density of the air/fuel ratio is also decreased as heat rises. To compensate, some vehicles pull out ignition timing automatically as cooling system temperatures rise. In other words, high temperatures rob horsepower.

We're not typically fans of miracle products that come in a bottle, or a can for that matter. But over the years we've become accustomed to using cooling system wetting agents, as they've been proven to work almost every time. Unlike ring sealers in a can and other mysterious leak sealing products that never seem to work, cooling system additives generally do work. But to answer the question as to just how well some of these additives get the job done and which reigns supreme, we decided to put four of them to the test.

Our test apparatus took the form of an EG Honda Civic with an H22A4 Prelude engine stuffed into place. A classic recipe for overheating since many transplant owners fail to upgrade the radiator despite the more than 40-percent larger displacement engine not to mention its sheer physical size increase. Our test vehicle took the necessary precautions - sort of. A thicker Del Sol Si VTEC radiator was swapped into place as was a higher flowing cooling fan, but that doesn't stop the Civic from escalating cooling system temps. With a 50/50 mix of Honda antifreeze and distilled water, temperatures soared to 215 F routinely while sitting in the drive-thru, and never really dropped below the 200 mark even under normal low engine speed driving conditions. Cylinder head temperatures were equally as scorching in the case of our Honda measuring in at nearly 210 F. As such, our radiator proved rather inefficient, only able to drop the system's temperature by a factor of five percent.

For our test we rounded up four of the most popular cooling additive products on the market: Red Line Water Wetter, DEI Radiator Relief, Hy-per Lube Super Coolant, and Justice Brothers Radiator Cooler. We tested these products mixed with both a 30/70 antifreeze/water mixture and mixed with water alone. The key to any successful test is keeping as many of the variables the same as possible, and performing as many tests as possible. Two days and nearly 300 miles later and we had our results, and some nasty burn marks on our arms. Note to self: allow more than two days when changing radiator fluid almost 10 times. Aside from outside air temperatures, which remained fairly constant during our testing, we were able to control almost everything else. We kept to the same roads, and stabilized load conditions by repeating similar engine and vehicle speeds for each test. We performed four tests for each mixture: Low rpm, low mph street driving; 4000rpm, 75mph freeway speeds; 5000rpm hill climbs; and extended idling. We also performed temperature readings for both radiator inlet and outlet temperatures and cylinder head temperatures. Now would be a good time to mention that none of these products are designed to perform miracles, and if your radiator isn't up to the task, don't expect anything but a new or larger radiator to fix the problem.

The results? This stuff works. All of them, but to different degrees and in slightly different ways. But there were stipulations. When mixed with coolant, our temperature drops were negligible, but still there. But with straight water, the temperature drops were nothing short of impressive. We expected this. There's no glycol-based antifreeze, or any liquid cooling agent for that matter, that we're aware of that can dissipate or transfer heat as well as plain old water. But you can't run plain old water, at least not without rusting or destroying your engine. Here are the highlights.

How They Work
Cooling system additives work by transferring heat more efficiently through the radiator. They can be used with an antifreeze/water mix or with water alone. They get their job done by reducing the surface tension of the cooling system mixture, which promotes thermal conductivity, or heat transfer by being able to penetrate heat-prone metal surfaces better. The process, called metal wetting, is also aided by an anti-foaming agent. We can run straight water with any of these products since they all have a corrosion inhibitor, which stabilizes the mixture's pH level. By balancing these negative acidic effects, you don't have to worry about rust, electrolysis, and deposits commonly associated with straight water mixes.