Jim Smart
August 13, 2014
Photos By: The Manufacturers

Some of the more common technical questions we get involve overheating, and with good reason. Overheating can be chronic, especially with older Mustangs. Classic Mustangs had marginal cooling systems from the factory. Combine that with the many misconceptions about cooling systems and you have a formula for overheating. Falcon-sized two-row-core radiators didn't offer enough cooling capacity for inline-sixes, let alone V-8s. Those wimpy 20-inch vertical tube radiators offered a convoluted coolant path that only aggravated overheating problems because it was not the ideal crossflow radiator, which is why Ford went to a more common sense crossflow radiator in 1970. Take that troublesome approach to radiators and add corrosion and you have a monumental problem with heat transfer.

Through the years, we have added insult to injury by instituting our own modifications thinking we were going to make things better. Instead, we've only made things worse. We've all seen it—incorrectly sized fans and spacers, fans without shrouds, radiators that should have been tossed ages ago, cylinder head gaskets installed backward, tons of silicone sealer where it doesn't belong, the absence of a thermostat or one of the incorrect temperature, and on and on it goes.

Basic cooling system function hasn’t changed much in more than 100 years of internal combustion. Coolant flows from the radiator into the engine via the lower radiator hose entering at the water pump. Heat generated by the engine is transferred into the coolant. When coolant temperature reaches the appropriate temperature, the thermostat opens, releasing hot coolant to the radiator where it is cooled by airflow and circulated back to the engine again.

Cooling system function is simple in scope. Remove more heat than the engine creates, yet not remove too much. Vintage Mustang engines like to operate around 180-200 degrees F coolant temperature. Later model engines like 195-200 degrees F for proper electronic engine control function. And this is where we like to see these engines function. To keep them there, you need a cooling system that will do it consistently well. This means just the right radiator sizing and proper fan selection.

Summit Racing Equipment and Flex-a-lite have a huge variety of cooling system enhancement products designed and engineered to meet your needs and we're going to show you how to get there. Because we've done a lot of cooling system articles through the years, we've learned what works and what doesn't. Your first order of business is to decide on an engine-driven fan or electric fan. Radiator selection is simply this—you can never have too much radiator. You want efficient radiator function to where engine temperature will be conservative even on the hottest day.

These are the basic staples of good cooling system maintenance—hoses, thermostat, water pump and gasket, hose clamps, and coolant. Never underestimate the importance of a healthy radiator. So many of us do engine rebuilds and forget the radiator. A crusty, corroded radiator hinders cooling ability greatly and you wind up with a new engine that runs hot thereby shortening engine life.
The thermostat is your cooling system’s traffic cop. It controls coolant flow from the engine to the radiator based on coolant temperature. A sealed wax capsule works against spring pressure to control temperature; the stiffer the spring the higher the thermostat’s temperature rating. Thermostats fail when the wax capsule leaks or bursts and they fail to open, hence the term “stuck thermostat.” Thermostats should be replaced every time you perform cooling system service or every two to four years.
To solve the dilemma of trapped air in the water jackets, some technicians drill a small 3⁄16-inch hole in the thermostat to allow air to burp into the upper radiator hose during initial start-up, which prevents hot spots. You can also buy performance thermostats with this vent feature built in.
There is a variety of 45-degree heater hose intake manifold fittings for classic Mustang V-8s. This is a Boss 302 heater hose elbow with a built-in restriction feature that prevents heater core overpressure and failure. Good common sense protocol is to restrict heater core flow in the interest of durability and service life.
Antifreeze manufacturers and automakers suggest a 50/50 mix of antifreeze and water to achieve a safe mix down to -34 degrees F. We’re going to take this a step further. If you choose the 50/50 mix go with distilled water, not tap water. Tap water often contains minerals and contaminants that can clog your radiator and cooling passages. Mark Jeffrey of Trans Am Racing tells us he has been using 100 percent antifreeze in his engines for years without consequence and with no corrosion. He comments he has seen slightly higher engine temperatures, but nothing serious enough to cause engine damage.
Classic Mustangs were typically fitted with these 20-inch, two-row core radiators, which were not up to the task for any length of time. This is a four-row-core OEM-style Mustang radiator from Scott Drake available from Mustangs Plus. The four-row-core design offers greater cooling capacity along with an original equipment look.
Radiator caps do more than just keep coolant inside, they work to contain cooling system pressure (to keep boiling point higher) and serve as a pressure relief valve when pressures meet and exceed the cap rating. Pay attention to the cap’s indicated pressure. Most classic Mustangs need only 13-16 psi.

Cooling System Filtration

New and rebuilt engine block, cylinder head, and manifold castings tend to shed iron and aluminum particles that can block radiator tubes and other passages resulting in overheating. A coolant filter/screen in the upper radiator hose will trap these and other debris particles, keeping them out of the radiator. A filter keeps your radiator out of harm's way. The pesky part of a coolant filter is periodic inspection and cleaning. Ignore it and it will clog, causing overheating. A coolant filter should be mandatory for any new engine/radiator combo being installed. All Mustangs should have some sort of coolant recovery system as well to catch excess coolant from the radiator. You can always install a coolant recovery tank in a hidden location. Do it to save coolant. Do it to protect the environment and animals who like the sweet taste of antifreeze.

This is The Trap Radiator Filter from Golan, Inc., which is located in the upper radiator hose between the thermostat and radiator. It will trap virtually all large solid contaminants like iron and aluminum, sealer, gasket material, and more. It is easily disassembled for cleaning.
The Gano Auto Coolant Filter goes in the upper radiator hose removing rust, aluminum, and other contaminants from the coolant that can clog radiator tubes. Service is simple by lowering the coolant level and flushing contaminants out of this virtually invisible filter available in 11⁄8- to 13⁄8-inch, 1½- to 1¾-inch, and 17⁄8- to 21⁄8-inch sizes in clear, aluminum, and brass.

Hose Tech

When you're in the market for cooling system hoses, it is best to be armed with the right information where you can make an educated decision. Hose quality is the best it has ever been in modern manufacturing history. All cooling system hoses are extruded rubber or silicone made in layers with fiber reinforcement between the layers. Goodyear, which makes a lot of cooling system hoses for the automakers and aftermarket, produces a lot of molded hoses for classic and late-model Mustang applications. Goodyear Hi-Miler silicone hoses stand up to more punishment than your average black rubber hose.

Goodyear molded and straight cooling system hoses are made of a Versigard rubber core and cover (EPDM), designed to resist heat, ozone, and harsh chemicals in coolants. And this is what you want from a good molded replacement cooling system hose. Never opt for cooling system hoses on the cheap. Specify the highest quality made to exceed SAE J20R4, D1 standards.

Not all cooling system hoses are made to the same standards. This is a reproduction radiator hose from Marti Auto Works, which offer OEM durability along with the correct factory markings.
Although we will get arguments on this one, there is but one right answer. Never assemble a Mustang’s cooling system without this anti-collapse spring, which is available from Marti Auto Works, NPD, and others. Although some hose manufacturers claim this spring was used for assembly line fast-fill—this is not true. The anti-collapse spring supports the lower radiator hose at high engine rpm when coolant is leaving the radiator faster than it can recover causing the hose to collapse. If you have an overheating issue on the open road but not in town, you might just need this anti-collapse spring.