Mark Houlahan
Tech Editor, Mustang Monthly
April 10, 2013
Photos By: The Manufacturer

Your Mustang's cooling system is one of the most basic systems of the internal combustion engine, be it a vintage or a late-model Mustang. The cooling system's function is a simple one; transfer the heat produced by the combustion process to an external heat exchanger, via fluid that is pumped through the engine via a pump, where the heat is radiated to the atmosphere with the help of a fan that pulls air through the heat exchanger. Yeah, that description was a little “shop manual-ish“, but you get the idea. No matter the year or model of Mustang you own, while the components may differ slightly, the cooling system is essentially the same. Whether it is a '66 Mustang with an inline-six or a '09 Mustang GT with a 4.6L Three-Valve, they all have a radiator, a water pump, hoses, a cooling fan, and coolant/anti-freeze.

What happens when you have a problem with your cooling system however? Be it a leaking water pump or perhaps an overheating problem, how do you find out what the problem is? Or perhaps you're building a restomod or modifying your late-model with a supercharger, how does this affect your cooling system? Do you have a radiator of sufficient size to transfer the heat your engine generates efficiently? What about your choice of cooling fan, or even the water pump and cooling hoses? These are all important decisions that need to be made to ensure your cooling system can handle your performance upgrades. Let's start with an overview of how the Mustang's cooling system works to keep your engine running at the proper temperature.

The Heart of the System
The water pump is belt driven on Ford engines and pressurizes the coolant passages of the engine block with coolant where heat from the combustion process transfers to the coolant and is then passed to the cylinder head(s). In a V-8, the coolant path travels to the rear of the block and then flows forward to the intake/thermostat and forced through your upper cooling hose to the radiator core where the hot 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 to the water pump to repeat the cycle.

The importance of a quality water pump cannot be underestimated. As the core of the cooling system, you shouldn't skimp on your water pump for your Mustang. If your water pump is of questionable history/age, it is a worthwhile investment to install a new high-flow unit. Look for quality hardware like a large bearing shaft, billet steel hub, CNC machined impeller (and not just a universal stamped steel one), and a quality casting. Don't rely on a $29 remanufactured parts store water pump to cool your high compression aluminum headed stroker!

The Cooling Cop
The cooling system's thermostat controls coolant flow through the engine and is essential to how the cooling system works. The thermostat controls the cooling system's flow through the block. When cold, the thermostat is closed and restricts coolant flow, allowing the block to warm up quickly (hot water is needed for cabin heater use, for example). Once the coolant in the engine has reached the appropriate temperature, the thermostat opens and allows the coolant to transfer to the radiator where the heat is dissipated. We highly recommend that all street driven cars use a thermostat of the proper rating. Typical thermostat ranges are from 160-degrees to almost 200-degrees. Modern EFI engines use higher temperatures, typically in the 192-195-degree range, while traditional carbureted engines will normally run just fine with 180-degree thermostats. It is 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 (or running no thermostat at all) is nothing more than a Band-Aid fix. Find the real root of the cooling system issue instead.