Cooling Tech Math - Cool Geek
Cooling Tech Math
There’s no buzzkill like a Jeep that overheats when you’re out on the trail, soaking in the beauty of nature and trying to mount the next obstacle. Or when you’re on the afternoon commute in traffic, for that matter. There is simply no good time for overheating, and for 99 percent of the Jeeps on the road, there’s no reason for it either. If you approach your cooling system with the same systematic approach as you do selecting gear ratios and tire sizes, it’s pretty easy to keep your engine cool.
First the basics: The engine creates heat. The more power the engine makes, and the harder you work the engine, the more heat is generated. That’s why a tow vehicle has a huge radiator—lots of power and lots of work. Some of the heat goes out the exhaust and some is radiated directly to the air, but most of the heat is removed from the engine through liquid coolant and transferred to the radiator. The radiator is designed to transfer as much of that heat as possible from the coolant to the air. The cooling fan draws additional air though the radiator to increase that heat transfer. It’s pretty simple, really.
The issue that we often run into is that Jeeps have tight engine bays, typically small space for a radiator, and we like to stuff big horsepower engines into them.
There are a few factors when considering the right radiator for your Jeep. First is the efficiency of heat transfer. The old tech was to add “cores” to increase heat transfer. This refers to how many layers of tubes the radiator has. In traditional radiators, the tubes were 3⁄8-inch wide, and a 2-core radiator would have two rows of these tubes. The problem is that as you add another row, you decrease the efficiency of each row. So a 4-core radiator doesn’t provide twice as much heat transfer as a 2-core. The last core has hot air passing over it from the first 3 cores, and the thick radiator is more difficult to move air through. Most modern radiators use 1-inch wide cores and come in either 1- or 2-row configurations for improved heat transfer. The other factor in the radiator core is how many cooling fins are attached to the tubes and the spacing and design of the fins. This is a balance, but generally the more fins you have per inch while not restricting airflow, the more heat the radiator will transfer.
Another key element in the radiator is coolant capacity. Most of the time, the factory radiator was the smallest needed in order to cool the stock engine. A larger radiator was a waste of material and added weight. It’s typical for an aftermarket radiator to double the coolant capacity. Not only does this add more coolant to the overall system, it increases the amount of the coolant that is in the radiator at any given time where it is rejecting heat, instead of in the engine where it is absorbing heat.
The fan is the next part of the cooling system you will want to consider. The goal with the fan is to move the maximum amount of air through the radiator. The key, though, is that the air needs to go through the radiator, not around it.
Belt-driven fans can move a ton of air and typically work better with the engine running above 1,500 rpm. The higher the engine revs, the more air the fan will move. The challenge with most Jeeps is that the fan shroud is gone because the fan hit it while we were off-roading or we’ve done an engine swap and there wasn’t a fan shroud available. Without a fan shroud, air will take the path of least resistance, which is over, below, and anywhere except through the radiator.
That’s one of the things that make an electric fan attractive. The electric fan mounts directly to the radiator, only pulling the air through the radiator. The other advantage of an electric fan is that it can pull maximum airflow with the Jeep idling. Some people don’t trust the electronics, but we think the technology has proven itself over the last several decades.
However, not all electric fans are equally good at cooling. The size of the fan blade and wattage of the electric motor determine how much air the fan can move through how much of an area of the radiator. Aftermarket fans are rated in cubic feet per minute (cfm) of airflow. There is not a standard for testing this, but it’s a decent way to compare electric fans. For most stock engines, you’ll want at least 2,000 cfm and more like 3,000 cfm if you live in Phoenix and have air conditioning. Most Jeeps with mild V-8s swapped in can use fans with 3,000 cfm of airflow. More airflow is usually better for cooling, but the design of the fan makes a difference, and the higher the airflow, generally the higher the amperage draw, which may dictate an alternator upgrade.
There are several other items in the cooling system that are important to consider. We share more information on that in the photos and captions. The bottom line is that it’s easier than ever to keep the coolant in your system and the heat out. Feel free to remind us of that if you see us on the trail with the hood up, letting off steam.