There are a number of things we seem to put up with in our pursuit of driving cool-looking cars. A ridiculously low car will induce a newfound fear of driveways and speed bumps for instance, or suffering lack of steering lock to avoid scrubbing tires against fenders, but sitting at the side of the road when your radiator has just spewed its contents because your cooling system is not up to the job at hand will very definitely not leave you looking cool. In fact it'll do just the opposite!
But for some reason most of us don't consider the radiator early enough in a project, which is crazy when you think how small most hot rod or custom engine compartments are, how we fill them with engines several times larger, both in physical size and capacity, than the original engine, and how they'll undoubtedly generate way more heat than the original. Yet we'll often reduce the number of ways for that heat to escape the confines of the bodywork. Smooth hood sides or inner fender panels, lower ride height and less space under the hood because we've added any number of air space-robbing components all contribute to a reduction in the ability for hot air to escape.
Of course we're focused on installing that new motor or front suspension, or whatever the UPS truck has just delivered, but early in any project we should be considering the radiator and planning for what's required to cool the combination we've just spent a fortune on, rather than leaving it until later and looking for a radiator that will fill the space that's left between the water pump and the backside of the grille. Because we can guarantee that space will not be sufficient in most instances, and that's asking for trouble down the road. Seeing as we mentioned grilles-ensure enough air can pass through the opening. We're not just talking customs here, which often have grille openings smaller than before any bodywork was performed, but hot rods too, such as track noses, sectioned grille shells, or semi-filled openings.
Though it's the radiator that you immediately think of when it comes to cooling, the cooling system consists of more than that one component. Coolant leaves the radiator, enters the water pump and is pushed through the engine, absorbing heat from the block, before passing through the thermostat, whose job it is to maintain the engine at a constant temperature, and back to the radiator, where that heat is dissipated as the coolant passes through it.
Old-style radiators that have the radiator cap on the high pressure side of the radiator, and thus subject to pressure from the water pump, would often expel coolant when the pressure at high rpm would overcome the cap's pressure rating, leading to the misconception that if coolant flowed too quickly through the radiator it would not have time to dissipate heat. But the system is a closed loop, meaning in that instance it would also travel through the engine too quickly, and therefore would not absorb as much heat either. Modern radiators place the cap on the low pressure side of the radiator where it is not subject to water pump pressure, thus benefitting from higher coolant flow.
There are two main aspects to consider when it comes to radiators-airflow through them and surface area. Ideally you want as much of both as possible, which is why planning for as large a radiator as possible at the early stages of a project is important. At the very least you will require a radiator that is the same as, and preferably larger than, the original radiator for your chosen engine, not the vehicle it's now in. So don't go expecting your original '53 Chevy radiator, which previously cooled a straight six, to be up to the task of handling that small-block 350 you dropped in there. Also, bear in mind that higher compression motors make more heat and need more cooling capability.
So what are your choices when it comes to radiators, apart from its size? One of the main choices is whether to go for aluminum or copper and brass. Copper is a better heat conductor than aluminum, and was the mainstay of radiator construction for the majority of our cars when they were new. It's also easier to repair than aluminum, though the latter is cheaper and weighs less. Though the majority of aftermarket radiators are constructed from aluminum, copper/brass versions are still available from companies like Walker Radiator and Brassworks, ideal looks-wise if you're building a traditional style rod without a hood. Advocates of each construction material will defend their choice, but selecting the correct design for your application is more critical than what it's made from!
Then there's the subject of how many rows of tubes your radiator core should have, though a radiator with a larger surface area will cool the water more quickly than a smaller, thicker core in the same situation, maximizing airflow through the latter will help matters. Of course you may not have an option to use a physically larger radiator. The luxury afforded those building cars with full width grilles that can accept a modern style crossflow radiator is lost on the owner of a Model A, or similar, as they have a certain size grille shell that the radiator has to fit in, which is where thicker cores with more rows of cooling tubes come in. Optimizing the airflow through that core is the secret to staying cool, which is where we come to fans.
 Most modern radiators are...  Most modern radiators are of a crossflow design, and AutoRad's new combination core support and radiator takes advantage of this to provide a bolt-in aluminum replacement for the '55-57 Chevy, providing 40 percent more surface area than the stock radiator. |  Brassworks make their own...  Brassworks make their own cores in copper and brass (though most are painted black) so any height, width or depth can be accommodated to provide the look and cooling capability required (they can also build from your patterns). Shorty street rod radiators can be supplied to fit stock or sectioned Ford radiator shells, with nickel-plated necks as per the originals, or with chrome or smooth tops. This '32 Ford Flathead radiator has an angled top header tank, and their '33-36 radiators are available with a fan well cutout like the originals. Options include A/C units, trans coolers, fans, polishing and formed shrouds. They use three or four row cores and are designed to use 15-18 psi caps. |  AFCO's '32 Ford radiator,...  AFCO's '32 Ford radiator, available from Speedway Motors, features wide tube core construction, with two rows of 1-inch tubes to maximize the tube-to-fin contact area. It also carries hood mounts, grille side mounts and ribbed feet, and is fully polished as standard. AFCO makes radiators for many street rod applications. |
 Extra room for a shroud is...  Extra room for a shroud is hard to come by under the hood of an early hot rod so you need to pay attention to how much space you have between the radiator and the front of the water pump. Cooling Components' 2,700 cfm electric fan and shroud is unique in that it has a maximum depth of just 2 5/8-inches, meaning it'll fit in the tightest of spaces. This could be a problem solver for many who thought they couldn't fit a shrouded electric fan. |  Although you're not going...  Although you're not going to squeeze Flex-a-lite's FLEX-A-FIT crossflow aluminum radiators into a highboy roadster you might be able to work one into a late-Fifties or Sixties custom. They're designed with internal fins that perform as heat sinks to absorb heat more quickly and then radiate it through external fins that increase the radiant surface threefold. The unique fin design integrates limitless fastening points for recovery tanks, fans, oil coolers, and even to mount the radiator itself, the brackets attached by bolts in the T channels in the sidetanks. |  The Brassworks can form a...  The Brassworks can form a galvanized steel (or a combination of metals) fan shroud to fit your custom-built radiator. The fans are mounted to the shroud to reduce vibration and can be mounted inside or outside depending upon your preference. The depth of the shroud can be varied to best work with your engine placement. |