Mark Houlahan
Brand Manager, Mustang Monthly
June 14, 2012

There's nothing that will ruin a day quicker than seeing your temperature gauge head north and smelling that heart-wrenching scent of coolant coming from under your hood. Cooling system issues are the bane of our world of customization and modification we call restomodding. From engine swaps and high-horsepower powertrains to custom front fascias/grilles and hoods, there are a lot of things that can affect the efficiency of your cooling system and its ability to shed the heat that your engine puts out.

Combustion chamber temperatures can reach 5,000 degrees. Aluminum will melt at 1,200 degrees, and iron at roughly 2,100 degrees. Therefore, the cooling system's main job is to prevent damage to your engine by getting rid of that extreme heat through thermal transfer from the surrounding metals to the water/coolant in the cooling system passages. Of course, there are the basic cooling system components to worry about too. Do you have a radiator of sufficient size to transfer the heat your engine generates? What about your choice of cooling fan, or even the water pump and cooling hoses? In order to effectively cool your restomod, these important questions should be answered with the entire system in mind.

Before we get into choosing the right parts, an overview of how the typical cooling system works is in order. We'll begin with the heart of any cooling system--the water pump. Driven by a typical V-style belt or serpentine belt, the water pump on Ford engines pressurizes the coolant passages of the engine block where heat from the combustion process transfers from the block to the water/coolant mixture. At the rear of the block, the coolant passes up into the cylinder heads and then flows up into the intake manifold and forward to the thermostat. Once the thermostat has reached its specified temperature, it opens to allow the coolant to flow through the upper hose to the radiator core. There, the hot water/coolant is cooled by ambient air forced through the fins of the radiator, either by ram air at speed or via a fan that pulls the air through the core.

After travelling through the radiator, the water/coolant is returned to the engine via the lower radiator hose and then to the water pump to repeat the cycle. The importance of a quality water pump can't be underestimated. As the heart of the cooling system, you shouldn't skimp on your water pump for your project. If your water pump is of questionable history/age, it's a worthwhile investment to install a new high-flow unit. Look for quality hardware like a large-bearing shaft, a billet steel hub, a cast/machined impeller (and not just a universal stamped steel one), and a quality casting. Don't rely on a $30 remanufactured parts store water pump to cool your high-compression, aluminum-headed stroker! Look to a high-performance piece to provide adequate flow. Nowadays, the aftermarket offers electric water pumps in addition to the traditional beltdriven versions. These offer great flow and great looks, but most of them were designed for race cars to cool the engine between rounds while the engine is not running. There generally is no pulley on these, so belt routing will have to be changed unless you buy an electric pump that utilizes an idler pulley.

The cooling system's thermostat is included for a reason, and we highly recommend that all street-driven cars use one. The thermostat controls the cooling system's flow through the block. When cold, the thermostat is closed and restricts water/coolant flow, allowing the block to warm up quickly (hot water is needed for cabin heater use for example). Once the water/coolant in the engine has reached the appropriate temperature the thermostat opens and allows the water/coolant to transfer to the radiator where the heat is dissipated. Using the proper thermostat rating is important. Typical thermostat ranges are from 160 degrees to almost 200 degrees. Modern EFI engines use higher temperatures, typically in the 192- to 195-degree range, while traditional carbureted engines normally will run just fine with 180-degree thermostats. It's rare these days a 160-degree thermostat is used, and using a lower-than-required thermostat in an attempt to fix a cooling system problem is nothing more than a Band-Aid fix. Find the real root of the cooling system issue instead.

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Choosing a Radiator

When it comes to radiators, there have been huge advancements over the years. From down-flow copper brass radiators to aluminum crossflow to hybrid radiators made from aluminum and plastic, the radiator is arguably the second most critical cooling system component behind the water pump. The most important factor when considering a radiator for your classic Ford is the surface area of the radiator core. Simply put, maximize your surface area for the best cooling efficiency. If your core size is smaller than your radiator support opening, you're not taking advantage of the available airflow opening/surface area. Once you've maximized the surface area of the core size, you can then go to a thicker core to further increase cooling. Keep in mind that adding core thickness does not increase the radiator's efficiency as much as maximizing the core's surface area, however. A thicker radiator core does have more resistance to airflow than thinner radiator cores, but the difference is typically minimal considering a 4-inch thick radiator core has roughly 10 percent more resistance to airflow than a 2-inch radiator core.

Core thickness has been blamed for decreased cooling many times, with the thought being that the airflow through the thicker core was decreased, and became fully heat saturated before exiting the core. Sounds great in theory, but usually what is happening is a decrease in coolant flow, not airflow. An older down-flow radiator design usually has a very narrow cooling tube design, which is fine with a stock water pump. When you move to a modern aluminum radiator with the wider coolant tubes, there isn't sufficient coolant flow to create turbulence in the tubes with a stock-type water pump. You need this turbulence to force the coolant against the outside walls of the coolant tubes for thermal transfer to the tube wall, and subsequently to the air passing over these coolant tubes. With the combination of a modern, large-tube radiator and a stock-flow water pump, the velocity decreases and you don't get the turbulence you need for proper heat transfer. If the core is doubled in thickness the coolant velocity is halved. Again, this is why we recommend the modern crossflow design, as it uses wide tubes with less cross section (thinner cores), which requires less velocity to achieve the needed heat transfer.

One thing many people don't consider when choosing a radiator is fin count. Yes, we want the largest core possible, but the fins between the cooling tubes of the core are what give the radiator surface area and help transfer the heat to the air passing through the core. The higher the fin count the better the radiator will cool. The main concern with higher fin counts is keeping the core clean of dirt and debris, as the higher fin count traps these insulators more easily, decreasing the efficiency of the radiator. When building a custom radiator to your specs, you will have to determine the best fin count for your application, although many custom radiator builders only have a few options to choose from.

The last thing to consider when it comes to radiators is whether to retain the original down-flow radiator style with tanks on the top and bottom, or to update to a more modern crossflow radiator. If there's room for a proper crossflow core design we recommend the crossflow design for the reasons mentioned previously, plus they position the radiator cap on the low-pressure side of the system. A high-flow pump can create high system pressures, which will force water/coolant past the radiator cap at high rpm. This is terribly common on down-flow radiators, which is why we also recommend the highest cap rating you can find if you're going to keep your standard down-flow radiator due to space constraints (the stock 13-psi cap doesn't cut it with today's engine rpm capabilities).

Caps and Coolant

Speaking of radiator caps, it should be noted that the fill cap needs to be the highest point in your cooling system. This isn't usually a problem with your typical small-block and down-flow radiator, but larger engines (dimensionally) and certain engine placement issues, like a modular engine swap, can sometimes mean the highest point in the system ends up somewhere in the cylinder head or intake manifold versus the radiator cap. If the top of the radiator is not the highest point in the system, then you must use a degas tank of some sort and mount it higher than the engine. If you're yanking a modular engine from a wrecked late-model Mustang, do yourself a favor and grab all of the stock cooling hoses and the degas tank from the car, and factor them into your build. It will save a lot of headaches down the road trying to figure out hoses, cooling issues, and so forth. The one thing you don't want to have is trapped air in your system. While trapped air is inevitable in a new build, it is imperative your cap is at the highest point to help extract the trapped air, as the trapped air will always seek the highest point. We've seen people raise one end of a car to move the trapped air out, or even add a radiator petcock to a coolant passage in their intake manifold to bleed out the trapped air.

As noted previously, the classic 13-psi cap you'll find as OE on classic Mustangs and Fords is not suitable for today's driving environment, and should be restricted to "show use" in our opinion. The higher the cap rating, the higher the system pressure, which raises the boiling point of the coolant and increases the ability for the coolant to transfer heat from the engine. Check with your radiator manufacturer and use the highest pressure cap the radiator is rated for. Don't be surprised to hear that performance radiators can often handle a 22- to 24-psi cap.

Water is by far the best "coolant" you can use in your cooling system. However, water alone does not inhibit corrosion, nor does it have the ability to raise the freezing point of water all by itself. This is why you need some form of cooling system corrosion inhibitor at the least and for cold climates the proper anti-freeze mixture to prevent the system from freezing solid. Believe it or not, a 50/50 mix, as many manufacturers recommend, is actually too high of a ratio for warm climates. If you live in a warmer climate a 70/30 water/coolant mix is better, or like we said, straight water with a conditioner/lubricant/inhibiting agent added to the system is preferred. Certain racing sanctions will expect you to run straight water to reduce cleanup times should your cooling system be compromised in some way on track.

Cooling Fan Choices

Having the biggest radiator you can fit in your engine bay and a high-flow water pump won't mean much without adequate airflow. In this regard, you have two avenues; electric cooling fans and beltdriven fans. Each category has its good and bad points. For most, the traditional beltdriven fan is what we're used to. The fan bolts to the water pump's hub and is driven by a pulley and belt combination. We've seen fans installed backwards, we've seen the wrong pulley ratio used (salvage yard pulley swap for example), and we've seen belt routings that don't put enough belt surface on the pulley, causing slippage. Of course, you can have too small of a fan, or a fan with not enough blades to cool as well. When using a beltdriven fan, we recommend the "A/C" style fan with deep curved blades to really pull the air through the radiator core. If you're using a beltdriven fan, then use a shroud, no excuses. Airflow will take the path of least resistance, and that can, and often will, mean around the radiator instead of through it. Ensure the fan blade pitch is half into the shroud and half out by changing or adding a fan spacer as required. This will also ensure the airflow is drawn through the radiator instead of around it.

Electric cooling fans are pretty much the norm on new cars these days. Just about everything but fullsize trucks have an electric fan or pair of fans. The Mustang has used an electric fan setup with multiple speeds since 1994 (that's nearly two decades now), so electric fans certainly aren't just for race cars or for added towing insurance anymore. Electric fans allow for more room in the engine bay and offer better control over your cooling system, as they are an "on demand' cooling device, only running when the thermostatic switch in the coolant stream deems the fan necessary (low speed driving, long periods of idling, and so on). In some instances, like modular V-8 swaps, they are mandatory since there's no way to mount a beltdriven fan to the engine's beltdrive system. There are essentially only two ways to mount an electric fan, either as a pusher or a puller; meaning on the engine side of the radiator pulling air through, or on the grille side of the radiator pushing air through. An electric fan is going to be more efficient as a puller, but if you must use a pusher type, ensure it has adequate core coverage and moves enough air for your application.

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When it comes to fan coverage, you want as much of the radiator core covered by the fan as possible, with a minimum of 70 percent. If a shroud is available for your electric fan(s) package, by all means use it. The shroud not only makes the fan more efficient, as it is pulling air through the entire core, but the shroud usually makes the installation of fan easier since the shroud reaches the mounting edges of the radiator itself. While we've all done it, the last thing you should use for any sort of long-term fan mounting solution are those plastic "through-the-core" plastic tie-wrap affairs. The weight of the fan, coupled with the vibration of it in use, can cause the fan to wear/cut through the radiator's cooling tubes when mounted in this manner. At the least, use solid mounting ears/straps and when at all possible, a shroud (1/4-inch deep at a minimum) is the best solution.

There's a fairly common misconception that S-shaped blades outflow straight blades on an electric fan. More often than not, the S-blade fan has a different motor on it, which increases the airflow cfm, so we're not comparing apples to apples here. According to engineers we spoke with at SPAL, straight-blade fans are usually the more efficient of the two styles if the motors are the same, however they do have a blade pitch that is slightly noisier than the S-blade style. No matter the size of the fan or the type of blade, it is going to make some noise. When you move air, you create noise.

When looking at electric fans, beware of cheap models that cut corners. On large diameter fans, you'll find a support ring to stabilize the blades so they don't flex and cut into your radiator core. Also, look for glass-reinforced plastic for the fan body and blades. This increases the stiffness of the unit as a whole, and prevents blade breakage. Lastly, a quality fan will often have an IP68 rating for dust and water intrusion. Many low-dollar fans aren't rated as such, and driving in rain can severely shorten their lifespan to a matter of months. Many electric fans come without any wiring or controls, leaving it up to the installer to determine how to control the fan. We recommend controlling an electric fan via a thermostatic switch in the engine. Fan wiring should be sized properly for the amp draw of the fan motor, and due to the rather high-amp draws of the typical fan, you should always use a relay to allow direct connection to the battery (properly fused) so that the thermostatic switch turns the relay off and on for fan control. Amperage is of particular concern when it comes to using used fans from the scrapyard. Many times, these fans will draw much more amperage than a quality aftermarket fan, and if you're still running the factory alternator, it simply may not be enough to keep the charging system operating properly.

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Radiator Upgrade

It's inevitable that the original single-core radiator in this '64 Falcon would not be able to keep up with the demands of the added horsepower from the warmed up small-block that now resides in the engine bay. The old radiator was quite possibly original equipment and had a good amount of buildup, which would certainly have a negative effect on flow.

To address this issue, we got in touch with the guys at Champion Radiators in Orange, California, and they suggested their aluminum two-row '60-'65 Falcon radiator (PN EC259, $159.98) built for those running a small V-8 (289 or 302) with a mild increase in horsepower.

The advantage of the aluminum two-row radiator over the single-row brass version is better heat dissipation through thermal conduction and greater flow. Another bonus is the weight advantage aluminum has over the heavier brass unit. This radiator is a direct bolt-in replacement, so all that we needed to do was swap the radiators, connect the trans cooler lines and coolant hoses, fill it up with coolant, and we would be good to go. Now the car cruises all day long between 170-180 degrees whereas before, we were sweating in traffic while watching the temp gauge quickly creep above 210 degrees.

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