Whether you live in sunny Los Angeles, rainy Seattle, or windy Chicago, the objective is the same—to keep your Mustang running its best. Part of that equation is an effective and efficient cooling system. Cool-running cars make more power (up to a point), generally get better mileage, and don’t cause your stress level to go through the roof due to a creeping temp gauge needle. Hot-running cars create a domino effect of problems, from detonation or pinging, to overheating and exploding radiator hoses.
This is particularly the case with many modified Mustangs, especially those built before 1994 with the wimpy two-row radiators. The stock cooling system is good for a stock engine, but not much more. High-performance engine parts increase the heat in the combustion chamber (that’s what makes power), which raises the coolant temperature; and the stock cooling system runs out of breath pretty quickly, leaving you stranded in the middle of the Ozarks with an erupting radiator.
We all know that factory gauges aren’t the most accurate, but they can still tell us a lot about how the car is running. Most pre-’94 Mustangs like to run (water temperature) between 190 and 200 degrees F, which translates into the water temp needle being at or around the M or A in NORMAL. SN-95s like to run a little hotter. The stock thermostats on the Fox bodies are 192-degree units, which means that as soon as the water/coolant reaches that temperature, the thermostat opens up to allow the water to circulate through the radiator and system. A popular mod is to swap out the stock thermostat in favor of a 180-degree ’stat, which is a quick and inexpensive way to knock off about 5 to 10 degrees.
In this story, we’ll shed some light on how your Mustang’s cooling system works, what products are out there to aid with cooling, and how to keep your cool the next time your radiator spills its guts out on the freeway.
The Thermostat
The reason that Ford installed 192-degree ’stats in the Mustang was purely from an emissions standpoint. A 192 ’stat keeps the engine-operating temp higher, which in turn helps the catalytic converters build up more heat, thereby generating a more efficient burning of hydrocarbons. As we mentioned earlier, a popular cooling system mod is installing a 180-degree thermostat in place of the factory 192-degree job. But if you’ve been to the parts store and noticed that they have 160-degree ’stats, you’ve probably been tempted to get one. The problem when you start getting into low-temp ’stats like this is that it stays open almost constantly, which makes the radiator’s job of transferring heat out of the water negligible. A little restriction through the thermostat keeps the water in the radiator longer, which lets it remove more heat before returning it back to the engine.
The same goes for removing the ’stat completely. We’ve had experience with this very thing and can tell you that the car will make some funky moves of the temp gauge without a thermostat. Editor Kinnan’s ’87 5.0 was continually having heating problems (the needle would rise and fall for no reason whatsoever). Thinking the thermostat was sticking, he removed the housing to find that a previous owner removed the ’stat. Installation of a 180-degree ’stat completely solved the problem.
Water Pump
The stock water pumps on most Mustangs do a fairly good job of pumping the coolant through the system, but if you want something a little sturdier and more reliable, look to some of the aftermarket companies like Edelbrock. Their Victor Series 5.0L Ford water pump PN 8840 is made of cast 356 aluminum, which is CNC-machined and heat treated to T-6 specs, making it strong and durable. The Victor’s water passages are also designed for max flow and pressure with equal distribution to both sides of the block, a big factor in efficient cooling.
Coolant
Although not an extremely detrimental issue, a good coolant-to-water mix can mean the difference between running at 200 degrees F or 10-15 degrees less. Most manufacturers and mechanics recommend that you use a 50/50 mix of antifreeze and water, a good tip. Many people don’t realize this, but adding more antifreeze will actually hurt cooling performance because of its lower boiling point than water. The main reasons that we are told to put in a mixture of antifreeze are because it has a lower freezing point (than water) and it prevents corrosion inside the radiator. So, if you’re one of those people who runs around town in a Mustang with a radiator full of coolant and wondering why the temp needle is too high, there’s your answer.