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Your Mustang's Cooling System and How to Improve Efficiency

Written By: Glenn Cope II

One of the most important mechanical systems on a car is also, very often, one of the most overlooked and neglected—your Mustang's engine cooling system.

How Does a Mustang's Cooling System Operate?

The coolant flows out of the radiator outlet near the bottom of the radiator and is pushed into the motor by the water pump. The coolant then travels through the block and up through the heads on its way toward the water outlet. Just behind the water outlet on most motors resides the thermostat. The thermostat regulates the flow of water, restricting the flow to the radiator until the water temperature reaches the point where it is fully open. Once fully open the hot coolant flows out of the motor to the inlet near the top of the radiator. The coolant then passes through the tubes of the radiator where it gives up heat to the passing airflow.

Your engine works just like a big air pump. Air comes in, fuel is added, and the mixture is ignited. The cooler the incoming air, the more dense it is which means you can add more fuel and make more power. Have you ever wondered why your car feels more powerful on cool fall days? That’s the reason why! Cooling is important on any engine, but it’s even more important on an engine with forced induction like your EcoBoost Mustang. When air is compressed, it heats up. Since the turbocharger is compressing the air to squeeze more into the engine, the post compressor air can be a lot hotter than the ambient air temperature. On a stock car this can cause a noticeable loss in power on warm days. When you tune the car and crank up the boost, the intake temperatures can get even hotter.

Army Chinook with S197 Mustang GT

Should I Use Water or Coolant?

On today's engines, cooling system maintenance is critical to the life of the engine. With the variety of metals used in your Mustang's motor, there has to be something besides the water in the cooling system to protect those metals from corrosion. There are a variety of different coolant formulas in a variety of colors in use by automakers, all with specific metal protection factors. It's not like the old days when you just grab the good old green stuff off the parts store shelf. Run the wrong coolant in your motor and you take the chance of damaging corrosion taking place.

Coolant Mustang Radiator Cap

What Coolant Should I Buy?

The best coolants to buy to maximize the cooling system efficiency and protection are the premixed ones with deionized water. You should never use tap water in your engine's cooling system, only deionized water. Deionized water has been purified of contaminants and the mineral elements have been filtered out, minimizing deposits that may collect in the cooling system that can block critical water passages in the motor or the cooling tubes of the radiator.

Mishimoto Liquid Chill 50/50 Pre-Mix Coolant for All mustangs

What is a Water Pump and What Does it Do?

Given the name of the piece in question, water pump, it’s easy to speculate on its use. If you’re thinking “the water pump pumps water”, you pretty much hit the nail on the head. To drive the nail all the way in, the water pump circulates coolant throughout the engine. Coolant is a mix of water and anti-freeze (usually a 50-50 mix). Anti-freeze is used to increase the boiling point of the water, to lower the freezing point and also to inhibit rust as the solution circulates through the engines passageways. Otherwise as the engine heats up, the water could very easily boil off, resulting in the engine overheating. In colder climates the water could freeze which could potentially crack the block. Thus anti-freeze is used to negate these effects.

To summarize, a water pump pumps coolant throughout your Mustangs engine, and the job of the coolant is to cool the engine, by drawing heat away as it passes through the many chambers. The water pump is an integral part of any liquid cooled internal combustion engine, as without it, the engine will quickly overheat and seize. Thus it is very important your water pump be in good working condition.

1999-2004 Mustang Water Pump
1999-2004 Water Pump

How Does the Water Pump Work?

In the case of our ‘Stangs the water pump is a mechanical design, driven via the accessory belt, right on the front of the engine. The accessory belt runs over the water belt pulley, which in turn is connected to the pump vanes inside of the water pump housing. From the moment you start the engine to the moment you turn it off, the water pump is spinning continuously. It draws coolant from the radiator and circulates it through the cooling system into the intake manifold, block, and heater core before returning to the radiator where the incoming air draws the heat out of the coolant and into the ambient atmosphere.

1996-2001 and 2005-2009 Mustang 4.6L Water Pump Installed
1996-2001 and 2005-2009 4.6L Water Pump

How do I Verify My Water Pump is Functioning Properly?

As previously mentioned, the water pump is an integral part to any internal combustion engine. If it fails, your engine can quickly overheat, causing major damage. For the most part, water pumps are very reliable and last many years. However, like any part, they can wear out. Luckily, there are some very easy tests we can do to check the health of our water pump. 

First, with the engine off, reach down to the water pump pulley, and gently push the pulley up and down. There shouldn’t be any play or wobble. If there is, that pump is wearing out. As the pump is driven by the belt, check that the accessory belt is in good shape too. If it is cracking, replace the belt. If the belt were to break while you were driving, although the water pump did not fail itself, it would stop cooling the engine.

Ford Motorcraft 2000-2004 Mustang Serpentine Belt

Secondly, grab a flashlight and look up at the water pump from underneath the car. Every water pump comes with what is called a “weep hole”. This hole is located at the bottom of the pump, and is a great health indicator. If coolant is dripping out of the hole, or there are stains around the hole, it is evidence the pump is wearing out. The weep hole is engineered solely for this purpose.

A final check you can do is to check the circulation. With the engine on and up to regular operating temperature, grab a towel and pinch the upper radiator hose. When you let it go, you should feel a surge of coolant passing through, letting you know coolant is circulating through your system.

Mishimoto Silicone Radiator Hoses for 1986-1993 Mustang GTs and Cobras
Silicone Radiator Hoses for 1986-1993 Mustangs

My Water Pump is Faulty. What do I do?

If your water pump has failed any of the tests above, it is time to replace it. The great thing is, it isn’t very hard given the location of the pump on the front of the engine. A determined do-it-yourselfer can get it done in an afternoon with basic hand tools, with plenty of time to spare before the game starts.

Replacing the Water Pump - the Factory Opinion

If you use your Mustang strictly as a daily driver to get from point A to point B then a factory replacement unit will be just fine. The stock water pump does a decent job keeping the coolant is motion on a stock or close to stock build. Another advantage of going with an OEM product is the cost will be fairly cheaper than the other options. They will cool your engine with no issue if you are just running a few bolt-on upgrades, and they are also more readily available and can be picked up at various local auto parts stores.

1994-1995 5.0L Mustang Replacement Water Pump
1994-1995 5.0L Replacement Water Pump

High Flow Aftermarket Mustang Water Pumps

If you decided you wanted a little more horsepower and have completed, say, a head and cam upgrade, went with a stroker kit, or you are running a very stout bolt-on car then a high flow water pump may be a better choice for you. High flow water pumps have redesigned impellers which allow it to cool the engine more efficiently. These products offer an increase in flow while reducing the amount of power needed for the water pump to operate.

High Flow Performance Water Pump for 1996-2001 & 2005-2009 4.6L Mustangs
High Flow Performance Pumo (right) vs. Stock (left)

Electric Mustang Water Pumps

Going with an electric water pump would be exactly what you are looking for if you mainly use your Mustang for racing. Some Mustang enthusiasts use them on daily driven cars but they are far more commonly seen on race cars because of the advantages. Electric water pumps are also the most expensive compared to the other choices so they may not be the best option on a budget build.

There are two main benefits of choosing an electric unit over an engine powered water pump. This first is they don’t drain engine power as they are not belt-driven. This gives electric water pumps their second advantage of being able to be turned on when the car is off, helping cool your Mustang between runs. Electric water pumps have different flow rates so make sure you select one that will efficiently cool your engine depending on your application. They are highly versatile and can also be controlled by a switch to maintain the desired temperate.

Mustang Electric Water Pump Installed
Electric Water Pump

2001 Mustangs: How to Identify the Water Pump Pulley

Mid-way through the production run for the 2001 model year Ford changed the design of the water pump on the 4.6L engine. The older style pump produced from 1996 to mid-2001 had a longer shaft. In January of 2001 the design of the pump was changed to a shorter shaft. This necessitated a change in the design of the pump pulley.

You should visually identify which pulley/pump you have before ordering a replacement. The old water pump pulley had a convex or "bowed-out" face. The new design has a concave or pressed in face. There is no exact changeover date for the pump and pulley. It is important to visually inspect your car to see which design you have. Supposedly the changeover occurred in January of 2001, but we have seen cars with identical January build dates and different water pumps and pulleys. We have also seen the old style pulley used in a few 2001 models, so be sure to check yours before ordering. Refer to the pictures below to see which pulley design you have and the right part number for your application.

Early Style 1996-2001 Mustang Water Pump
Early Style 1996-2001 Water Pump
1996-2001 Mustang Late Style Water Pump
1996-2001 Late Style Water Pump
2001-2004 Mustang Late Style Water Pump
2001-2004 Late Style Water Pump

A Note About Reverse Flow Water Pumps

Reverse flow pumps were introduced at the same time of the release of the serpentine belt system. For mustangs, this year was 1979. The primary difference between reverse and regular flow pumps is simply the direction of flow and the flow of the pump itself.

Should I Run an Aluminum Radiator in My Mustang?

Radiators or, more technically correct, heat exchangers take the excess heat away from the engine and release this heat to the air. For the most part, radiators in today's cars are made with an aluminum core with composite tanks. These radiators are lighter, stronger, and more efficient than the copper brass radiators once used. They are also a good deal less expensive to produce. A few cars use all aluminum radiators and most aftermarket performance radiators are also made entirely of aluminum. The other advantage to aluminum radiators is the aluminum dissipates heat so well, the radiator cores can be smaller, yet still offer the cooling capacity of larger copper brass units. Another advantage to aluminum is that it is very easily recycled, an ever growing concern in today’s world. One disadvantage is that aluminum corrodes very easily so proper coolant mixtures are critical.

One other thing to take into account when purchasing a radiator is transmission type. A radiator intended for a manual transmission usually differs slightly from that intended for an automatic car because of the extra transmission cooler needed for the automatic transmission. Some radiators are universal, but not all, so just keep that in mind.

Now, one drawback to aluminum is that it can be somewhat brittle. Road vibration and bumps can stress the radiator and cause it to crack and then leak. This is why it is very important to purchase a quality radiator with quality welds. A poorly made radiator will let you know sooner rather than later, sometimes leaking right out of the factory!

Advantages:

  • Lighter, stronger and more efficient
  • Lower cost
  • Better heat disbursement
  • Larger cooling capacity
  • Easily recycled

Disadvantages:

  • Easily corroded (another reason to use the proper coolant!)
C&R Aluminum Mustang Radiator
Aluminum Radiator

How Effective are Aftermarket Radiators?

Engines produce a ton of energy which means heat is an issue. This issue is tackled with a water type cooling system. In these systems, radiators are used to cool the water off as it cycles through the system. 

When looking to boost an engine's power output, the radiator will have a harder time cooling the water within and then it’s time to look toward an aftermarket unit. With aftermarket radiators, one can go too far and lower the temp a bit too much meaning they are ineffective. The trick is not to go too far. 

Many aftermarket companies use percentages to show how much more efficient their radiator is in comparison to the stock unit. The trick is to stay within bounds. If the engine is mildly modified but is having cooling issues because of the factory unit, you don’t have to drop in something way over the top. Just something that is a mild step up.

When Does My Mustang Need Better Cooling?

Generally, for basic modifications a stock cooling system is substantially adequate. They perform quite well and last a long time. However, if an engine is being custom built or having a supercharger/turbocharger installed, it might be a good idea to upgrade the radiator and water pump. Utilizing something such as an aluminum radiator does a solid job of dissipating heat and keeping operating temperatures at a respectable level.

For a daily driver, it will hardly be necessary. For a racing application however, cooler temperatures never hurt to attain when highly modified. If you plan on doing some heavy road racing, looking into a differential cooler could be a solid idea. They generate some heat and while normally not an issue, over prolonged periods of high rpm it can get hot.

Stock Mustang Thermostat Temps and Fan On/Off Temps

Mustang Gen Thermostat Temp Fan On/Off
Foxbody (1979-1993) 190 -
SN95 (1994-1998) 180 221/-220
S197 (2005-2014) 180 228/-216
S550 (2015-2019) 180 228/-216

What is an Intercooler?

An intercooler is basically a radiator or heat exchanger. It is usually located on the front of the car in front of the engine’s radiator. When the intake charge from the turbo travels through the intercooler (air to water type), the heat of the intake charge is dissipated through the cooling fins. This results in a cooler, denser intake charge. 

Types of Intercoolers:

  • Air-to-air: mounts before the throttle body, good for turbos and centrifugals
  • Pros and cons: Reliable, but not as efficient as air-to-water
  • Air-to-water: utilizes the engine’s coolant to cool the intake charge, good for top mount superchargers
  • Pros and cons: can bring temps below ambient air temps, but for daily street machines heat soak is possible
Turboed 2014 Mustang on the Dyno at the AM Show

Air-to-Air Intercoolers

There are two types of intercoolers out there, air-to-air and air-to-water. In an air-to-air intercooler, the intake charge itself travels through the intercooler and then enters the intake plenum through the throttle body. As the air is forced through the intercooler, the heat is dissipated via the fins of the intercooler. They are generally used on turbocharged and centrifugal supercharged applications.

Turboed Drag Mustang at the AM 2014 Show

Air-to-Water Intercoolers

An air-to-water intercooler works much like the engine’s radiator. Water circulated by a pump is circulated through the intercooler, effectively cooling the intake charge. Typically these are used on twin-screw and whipple type superchargers. There is a heat exchanger located in the intake plenum, under the supercharger. The water absorbs the heat from the intake charge, and carries this heat to the intercooler where it’s released. Cool water is then pumped back to the intake plenum.

Whipple Supercharger on a Coyote Powered Mustang

Air-to-Water Pros and Cons

Since a whipple, or twin-screw style supercharger mounts directly to the top of the engine, the air-to-water set-up is about the only option available. Ford chose this type of intercooler for the Eaton supercharged ’03 Cobra, and it has proved to be very efficient. Many drag racers like this set-up because it allows them to run ice water through the intercooler. This will cool the intake charge lower than the ambient temperature outside.

On street applications, icing the intercooler coolant is not really an option. And after a while, the coolant becomes a bit warm. This causes heat soak in the supercharger. Although it won’t cause engine damage, it does result in a power loss. There is a noticeable difference in power and torque when the coolant hasn’t warmed up yet.

Pros:

  • Very high efficiency
  • Efficiency can be exaggerated by using ice, or other chemicals to produce lower temperatures
  • Can be mounted anywhere along the charge pipe route.

Cons:

  • Requires a water pump, a reservoir, a heat exchanger, et cetera
  • Since it is more complex, it naturally causes more opportunities for problem, like leaks
  • Can become heat-soaked when used for long period of hard driving
  • Since it uses water, and additional components, this set-up weighs more
2003 BAMA Mustang Cobra Project Car

Air-to-Air Pros and Cons

The air-to-air intercooler has gained popularity due to its simplicity and reliability. There is no need for an external pump, and as long as the intercooler unit is in good working order, it functions without a hiccup. Many mustangs prefer this unit for street use because of the reliability factor.

The main drawback of the air-to-air intercooler is the limited cooling capability. Due to the fact it uses air to cool the intake charge, intake temps really don’t get any lower than the ambient temperatures outside. They’re also quite bulky, so they take up a little more room.

Pros:

  • Requires no power to work
  • Easier to set-up
  • Requires no liquids to work and therefore, no chances for leaks
  • Does not suffer from heat-soak as long as the intercooler is seeing sufficient air-flow

Cons:

  • Efficiency is only as good as the ambient temperature
  • Efficiency is only as good as the amount of airflow the intercooler is exposed to
  • Cannot be mounted anywhere; must be mounting in an area that is exposed to high volumes of air flow
Shelby 1000 Mustang with an Air-to-Air Intercooler
 

Are Intercoolers Needed for Boosted Mustangs?

Yes and no. Technically, they aren’t needed in order for the blower (or turbo) to function. However, the amount of heat generated creates something commonly referred to as heat soak. Heat soak is the point where the engine bay is so hot, cool air cannot be taken into the engine. As a result of heat soak, power loss occurs, even if the same amount of boost is applied. In hot climates, heat soak can set in fast, which takes away power and isn’t the best feeling in the world. As a result, intercoolers are strongly recommended for those applications. If the engine is in a cooler, dry climate where temps do not get very high in the summer, the possibility of running without an intercooler is feasible. However, having an intercooler never hurts, it can only benefit. On the other hand, there's no reason to intercool a stock Mustang.

Where are Intercoolers Installed?

That can vary based on the type of boost and the design of the car itself. There are intercoolers that are air to air intercoolers. These are generally placed where there is maximum airflow in order to have the most efficient cooling. An example of this would be comparable to a radiator, where it is placed in order to have the most airflow. Intercoolers can sometimes be installed below the radiator, which also gives it the most airflow in the engine bay. Another example of an intercooler is an air to water intercooler. These are generally installed inside the manifold of supercharged applications after compression has taken place. This transfers the heat from the air to the water. The piping then flows to another intercooler that is water to air based. As you can guess, the opposite happens. The heat is transferred from the water to the air (at this point the air is the atmosphere). The transfer also allows the air to cool the water down and to begin being processed again to the manifold itself. In layman’s terms, the water passes through the intercooler and gets heated up. It then goes to the water to air intercooler where it is cooled down and goes back to the reservoir (of coolant) to get picked up and processed again. 

Does the Size of the Intercooler System Matter?

Absolutely the size matters! While having too large of an intercooler plumbing system can decrease velocity and also have the potential for boost spikes. This is because having an intercooler generally lowers the PSI, although retaining the same power. This can coincide with lag as well. If the system is too small, the engine will continue to heat soak as a result of the intercooler not being able to keep up with the amount of heat being generated. The charge pipe (the pipe directly after the turbo) can quickly become too small. This becomes a choke point and the entire system will suffer as a result. This is the only exception where, generally speaking, the piping cannot be too big. The limiting factor of charge piping sizing is the actual clearance inside the engine bay.

Are Intercooling Systems Easy to Install?

If you get an intercooling system as a part of a set (IE: A complete supercharger kit), they can be pretty basic to install. In many cases, they are plug and play and everything lines up somewhat easy. If you are getting an off the shelf universal intercooler, modifications might need to be made in order to allow for proper fitment and clearances. Another issue with installing intercoolers is for heavily modified vehicles. When plug and play kits are made, they are made to fit the stock engine. Having multiple modifications (several, really) can occasionally allow for fitment issues. 

Does My EcoBoost have an Intercooler?

Yes, it does! From the factory, Ford wanted the Ecoboost to be driven in all areas, under all conditions. As a result of that thought process, an intercooler was incorporated into the turbocharged system. Additionally, there are upgrades that can be made to the intercooler in order to make it more efficient and also save some weight in the process (intercoolers can become heavy).

The stock EcoBoost cooler is barely adequate for a stock engine, and testing has shown that intake temperatures can get around 170º-190º with the stock intercooler. These intake temperatures are insane, and the lower density of the air will result in reduced power, while the temperature will cause the computer to pull ignition timing. Installing a larger intercooler will drastically reduce the intake air temperature, bringing it down reasonable levels, around 100º. The reduction in intake temperatures can add 20-30 rear wheel horsepower on an otherwise bone stock Mustang, with no tuning needed.

Does an Intercooler Add Power?

It does not in most cases! The PSI will drop from the addition of the intercooler, but the cooler temps will, in turn, become more efficient for the engine. The result is the same amount of power for half the PSI and no heat soak!

Mustang Oil Coolers

Oil is used to keep things cool as well, and in particular, turbos. This results in no idle times when turning the car on or off since the turbos are essentially liquid cooled. Oil cools the engine by preventing metal on metal friction. While not only keeping the engine alive as a result, it also removes friction which in turn lowers the temperatures created by moving parts. For a Mustang that sees a lot of track time, an oil cooler is a must. An engine oil cooler will help keep the engine cooler as well by increasing its oil capacity, and by circulating the oil through a radiator. Heat causes oil to break down faster and reduces the protection it offers. Keeping your oil cool will extend its life and keep your engine protected. The increased capacity will also allow the oil to absorb more heat. 

What is the Ideal Operating Temperature for a Mustang's Motor Oil?

The optimum motor oil operating temperature for the Ford Mustang ranges from about 180 degrees to about 210 degrees Fahrenheit. At less than 180 degrees the oil doesn't flow as well resulting in increased wear and above 210 degrees the viscosity drops. As such, keeping your oil temperatures within this optimal range is very important. 

As oil temperatures rise, viscosity drops and the oil film between the moving parts thins. If oil temperatures become excessively high the loss of viscosity can lead to metal to metal contact and greatly decreased motor life. This is where installing a performance oil cooler on your Mustang comes into play.

Should I Get an Aftermarket Oil Cooler for My Mustang?

For the average Mustang driven normally, the factory oil system is adequate at maintaining the oil temperature in the proper range, but any extra stress added to the motor's job, such as towing or performance use, and the oil system needs help keeping temperatures under control. This is where a well-designed oil cooler comes into play and there are a number of different designs for oil coolers. Often, OEM Mustangs use an oil cooler that circulates engine coolant through a housing that the motor oil passes through. This style of cooler works to a point but has a limited capacity. Better cooling is achieved by a good aftermarket oil cooler.

Types of Mustang Oil Coolers

There are a few types of oil coolers generally used in the aftermarket, one being the tube and fin design, another is a stacked plate design, as well as some other less often used types such as heat sink designs. At the low end of the price range you will generally find the tube and fin coolers with the stacked plate designs costing more. Also, the high-end oil cooler kits will include a thermostat so that the oil will bypass the cooler at low temps helping to get the oil up to operating temps quicker. Most aftermarket oil cooler kits come with an adapter that fits on between the oil filter and the oil filter mount on the motor. From this adapter, hoses will be attached to connect the oil cooler itself to the oil system. The oil cooler needs to be mounted where it will receive good airflow. Most choose to mount the oil cooler in front of the radiator where the coolest air is flowing in as the car rolls down the road.

Facts About Performance Oil Coolers for Mustangs

  • The optimum motor oil operating temperature ranges from 180’ to 210’ Fahrenheit
  • For normal, daily driving, the factory oil system is adequate for cooling
  • For towing or performance use that puts added stress on the motor, an aftermarket oil cooler should be considered
  • There are two types of oil coolers generally available: tube and fin design and stacked plate design

Other systems on your Mustang can also benefit from aftermarket oil coolers, such as the transmission, power steering, and rear axle. All Mustangs that come from the factory with automatic transmissions will have a transmission oil cooler already installed, but most are just a simple looped oil line inside the tank on the radiator. These vehicles will reap great benefits with an aftermarket oil cooler added as these are much more efficient than the factory oil cooler.

A good oil cooler is definitely something to consider adding to your performance-minded Mustang as it will allow the motor to live longer and perform better.

Mustangs with Factory Oil Coolers

Most oil coolers came on specialty models. This models include the 96-01 Cobra, 03-04 Mach 1, 03-04 Cobras, 2012-2013 Boss 302, 07-14 GT500, etc. Oil coolers are primarily used in DOHC applications. This is because of the much higher amount of heat generated in the cylinder heads, which can be absorbed by the oil. In pushrod applications, they were not as common unless the engine was highly modified.

Fitment includes: 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, GT, V6, Cobra, ShelbyGT500, Mach1, Bullitt, Boss, LX, SVO, EcoBoost, ShelbyGT350