Introduction

Upgrading the cooling system on your 2020 Ford Mustang is one of the most effective performance enhancements you can make, especially if you track the car or live in a hot climate. The factory radiator, while adequate for daily driving, often struggles to maintain optimal temperatures under sustained high load. Replacing it with a Mishimoto aluminum radiator offers superior heat dissipation, increased coolant capacity, and long-term durability. This guide provides a complete, step-by-step walkthrough for installing a Mishimoto aluminum radiator in your S550 Mustang. Whether you are a seasoned DIYer or a first-time modifier, these instructions will help you get the job done safely and correctly.

Before starting, note that this guide assumes you have basic mechanical skills and a clean workspace. Always consult your vehicle’s service manual for torque specifications and specific model variations. For reference, the Mishimoto radiator for the 2015–2023 Mustang GT, EcoBoost, and Shelby models is a direct-fit upgrade that requires no cutting or drilling.

Tools and Materials Needed

Having everything on hand before you begin prevents unnecessary trips to the tool store and keeps the installation smooth. Below is a comprehensive list of tools and supplies. Some items, like a coolant funnel and vacuum refill kit, are optional but highly recommended for a clean fill.

  • Mishimoto aluminum radiator (part number MMRAD-MUS-15 for GT, verify fitment for your engine)
  • Socket set (metric, 8mm, 10mm, 13mm, 15mm)
  • Wrench set (combination wrenches, 10mm and 13mm most common)
  • Flathead screwdriver (medium size)
  • Phillips screwdriver (#2)
  • Coolant – Use Ford-approved Motorcraft Orange Antifreeze/Coolant (prediluted) or a high-quality concentrate mixed 50/50 with distilled water. DO NOT use universal green coolant.
  • Drain pan (minimum 2-gallon capacity)
  • Shop towels or rags
  • Safety glasses and mechanic’s gloves
  • Trim panel removal tool (optional for accessing some clips)
  • Needle-nose pliers (for hose clamp removal)
  • Coolant funnel (Lis 24680 or similar) – helps prevent air pockets
  • Distilled water (if mixing concentrate)
  • Torque wrench (for final bolt tightening)

You can purchase the Mishimoto radiator directly from Mishimoto’s website or from authorized retailers. For coolant selection, consult your owner’s manual or the Ford service information site.

Preparation Steps

Proper preparation reduces risk and saves time. Follow these steps before touching any parts:

  • Ensure the engine is completely cool. A hot cooling system is under pressure; opening it can cause severe burns. Wait at least one hour after the last drive, or preferably overnight.
  • Park on a level surface and engage the parking brake. This prevents the car from rolling and ensures you get an accurate coolant level reading later.
  • Disconnect the battery negative terminal. Use a 10mm wrench to loosen the clamp, then tuck the cable away from the terminal. This prevents any short circuits or accidental airbag deployment while working near the front of the car.
  • Remove any front under-tray or belly pan if equipped. The 2020 Mustang GT typically has a plastic cover under the engine. Remove the 10mm bolts and pushpin fasteners to access the drain valve and lower hoses.
  • Lay down cardboard or a drop cloth to catch any drips. Coolant is toxic to pets and slippery on concrete.
  • Inspect the old radiator for leaks or damage as you work; this helps identify any hidden issues with the cooling system.

For more detailed vehicle specifications, you can refer to the Ford Owner portal with your VIN.

Draining the Coolant

Draining the old coolant is straightforward but requires caution. The factory coolant is orange and should be disposed of properly. Do not pour it down the drain or onto the ground.

  1. Place your drain pan directly under the radiator drain valve. The valve is located on the bottom driver-side corner of the radiator, typically a white or black plastic petcock.
  2. Remove the radiator cap. This allows air into the system and speeds up draining. Turn the cap counterclockwise slowly to release any residual pressure.
  3. Open the drain valve by turning it counterclockwise with your fingers or a flathead screwdriver (depending on design). Let the coolant flow into the pan. It may take 2–3 minutes to fully drain.
  4. After draining, close the drain valve by turning it clockwise. Do not overtighten; hand-tight is sufficient.
  5. If you plan to reuse the old coolant (not recommended), filter it through a clean funnel and store it in a sealed container. Otherwise, transfer the drained coolant to a sealed container and take it to a recycling center.

Pro tip: To drain more coolant from the engine block, you can remove the lower radiator hose briefly after the radiator is empty, but be prepared for a small amount of coolant to spill. This step is optional but helps if you are switching to a different coolant type.

Removing the Old Radiator

With the coolant drained, you can now remove the factory radiator. The S550 Mustang uses a fairly simple mounting system, but there are a few tricks to make removal easier.

Disconnect Hoses and Electrical Connectors

  • Upper radiator hose: Loosen the clamp (spring clamp or worm-gear) at the radiator neck. Slide the clamp up the hose and twist the hose to break the seal, then pull it off. Be careful not to damage the plastic radiator neck.
  • Lower radiator hose: This hose connects to the bottom of the radiator on the passenger side. Use pliers to compress the spring clamp and slide it down the hose, then work the hose off the fitting. Some coolant may still drip.
  • Transmission cooler lines (if equipped with automatic transmission): The factory radiator has two metal lines that run to the cooler. Use a 13mm line wrench to disconnect them. Expect some fluid loss – place a rag underneath. Cap the lines with rubber caps or tape to prevent debris entry.
  • Electrical connectors: Disconnect the coolant level sensor (if present) and any auxiliary fan connectors attached to the radiator shroud. Press the tab and pull straight.

Remove the Radiator Mounting Bolts

The radiator is held in place by two upper brackets and sometimes a lower mount. On the 2020 Mustang, you’ll see two bolts on top (10mm or 13mm) that secure the brackets to the radiator support. Remove these bolts and lift the brackets out. The radiator will now be loose, but the lower rubber grommets may still hold it in place.

Lift Out the Old Radiator

  • Carefully tilt the top of the radiator toward the engine (about 30 degrees) so you can slide the lower tabs out of the mounting rubbers.
  • Lift the radiator straight up and out of the engine bay. It helps to have a second person if you are concerned about scratching paint or fins.
  • Place the old radiator aside. Do not discard it immediately – you may want to reuse the fan shroud or brackets (though the Mishimoto unit typically comes with its own brackets).

For a visual reference, the Mustang6G forum has several write-ups with photos that can clarify the bolt locations.

Installing the Mishimoto Aluminum Radiator

Now you are ready to install the high-performance replacement. The Mishimoto radiator is a direct fit, but there are a few specific steps to ensure it aligns perfectly and does not leak.

Transfer the Fan Shroud and Cooling Fans

If your Mishimoto radiator does not come with an integrated fan shroud (some kits include one, but the standard aluminum radiator requires transferring the factory shroud), you will need to remove the fan assembly from the old radiator and attach it to the new one.

  • Place the old radiator on a clean surface. Remove the fan shroud by undoing the bolts (usually 8mm) along the top edge and any clips along the sides.
  • Disconnect the fan motor wiring from the shroud if needed.
  • Position the fan shroud onto the Mishimoto radiator. The mounting points should line up perfectly. Secure it using the same bolts. Do not overtighten – aluminum threads are softer than steel. Use a torque wrench and set to 6–8 Nm (about 5 ft-lbs) if specified.
  • If your Mishimoto unit includes a separate lower support bracket, install it now following the included instructions.

Install the Mishimoto Radiator in the Vehicle

  1. Lower the new radiator into the engine bay, aligning the bottom mounting pins with the rubber insulators on the lower radiator support. You may need to tilt it slightly to get the pins to seat.
  2. Once seated, push the radiator back upright so it is vertical and centered.
  3. Install the upper mounting brackets. The Mishimoto kit usually comes with new aluminum brackets that are thicker than stock. Place them over the radiator top pegs and secure them with the provided bolts. Tighten to the specified torque (typically 8–10 ft-lbs, check the Mishimoto manual).
  4. Reattach the electrical connectors for the coolant level sensor and the fan motors.

Reconnect Hoses and Transmission Cooler Lines

  • Install new hose clamps (Mishimoto often supplies constant-tension clamps). Slide the clamps onto the hoses before attaching them to the radiator.
  • Attach the lower radiator hose first. Push it fully onto the aluminum fitting, then slide the clamp into position and tighten.
  • Attach the upper radiator hose. Ensure it is seated fully and the clamp is snug.
  • For automatic transmission cars, reconnect the cooler lines using new O-rings if supplied. Tighten the flare nuts to the proper torque (around 18 ft-lbs) using a line wrench. Avoid cross-threading.
  • Inspect all connections for any signs of misalignment.

Note: Some 2020 Mustangs have a secondary coolant tank (for the intercooler on EcoBoost models) – ensure those hoses are also reconnected properly.

Refilling the Cooling System

Refilling is more involved than just pouring coolant in. Air pockets can cause overheating, so use a proven method.

Bleeding the System (Burp Method)

  1. Close the drain valve and ensure all hose clamps are tight.
  2. Locate the coolant reservoir. Remove the cap.
  3. Pour the pre-mixed coolant slowly into the reservoir until it reaches the “MAX” line. Also, fill the radiator itself through the filler neck (if accessible). On the Mustang, the filler cap is on the top passenger side of the radiator.
  4. Start the engine and let it idle with the heater set to maximum temperature and fan on low. This opens the heater core valve and allows trapped air to escape.
  5. As the engine warms, air bubbles will surface in the reservoir. You may see the coolant level drop. Top it off as needed. Be careful not to overfill when the system is hot – wait for it to cool for accurate level readings.
  6. Run the engine for 10–15 minutes. Squeeze the upper radiator hose periodically to help burp air out. If you have a coolant funnel, attach it to the filler neck to make this process easier.
  7. Once the thermostat opens (you can feel the upper hose getting hot), turn off the engine and let it cool completely.
  8. Check the coolant level again; the reservoir should be at the cold fill line. Add coolant as necessary.

Some Mustangs require a specific bleeding procedure if you have an electric coolant pump (like the GT350). Consult your service manual.

Final Checks and Test Drive

Before putting the car back on the road, perform these checks to ensure everything is safe and tight.

  • Leak check: With the engine cool, inspect all hose connections, the drain valve, and transmission cooler lines for any drips. Start the engine and let it reach operating temperature, then recheck while the system is pressurized.
  • Verify fan operation: With the A/C on, the cooling fan should cycle on and off. Ensure the fan speeds are normal and there are no obstructions.
  • Reinstall the under-tray (if removed) using the original fasteners.
  • Reconnect the battery negative terminal. Tighten the clamp.
  • Scan for trouble codes: If you have an OBD-II scanner, check for any coolant temperature sensor or fan-related codes before driving.
  • Take a short test drive (5–10 miles) with a mix of city and highway speeds. Monitor the coolant temperature gauge. It should remain steady, typically near the middle of the range. For 2015–2020 Mustangs, the ideal operating temperature is around 190–210°F (87–99°C).
  • After the drive, park and allow the engine to cool. Recheck the coolant level and top off if necessary.

Performance Benefits and Maintenance Tips

Installing a Mishimoto aluminum radiator provides tangible improvements over the factory plastic-and-aluminum unit. The all-aluminum core with a 2-row design increases surface area for heat transfer. Many owners report a reduction in coolant temperatures by 10–20°F under hard driving conditions. The increased coolant capacity (typically +30% over stock) helps stabilize temperatures during prolonged track sessions. Additionally, the welded aluminum construction eliminates the common failure point of plastic end tanks cracking over time.

To get the most out of your new radiator, consider these maintenance tips:

  • Use only the correct coolant – Ford Orange (OAT) or a compatible high-performance coolant like Mishimoto’s own coolant. Never mix coolants of different colors.
  • Flush the cooling system every two years or 30,000 miles to prevent corrosion and scale buildup.
  • Inspect the radiator fins regularly for debris (bugs, leaves) and clean them gently with a soft brush and water. Avoid using high-pressure washers directly on the fins, as they can bend and reduce airflow.
  • Check the torque on the radiator mounting bolts and fan shroud bolts after the first 500 miles – aluminum can settle slightly.

Frequently Asked Questions

Will the Mishimoto radiator fit my 2020 Mustang EcoBoost or GT?

Yes, Mishimoto offers specific part numbers for the 2.3L EcoBoost (MMRAD-MUS-15EB) and the 5.0L GT (MMRAD-MUS-15). The GT350 and GT500 use different units. Always verify fitment with your VIN on the Mishimoto website.

Do I need to upgrade the cooling fans as well?

Not necessarily. The stock fans are sufficient for most applications. If you are doing heavy track duty or have a supercharger, an aftermarket fan controller or a higher-flow fan kit may be beneficial. Mishimoto sells a fan shroud kit separately.

Can I install this radiator without removing the front bumper?

No, you do not need to remove the bumper on a 2020 Mustang. The radiator can be lifted out from the top after removing the upper air deflectors and brackets. However, some owners find it easier to remove the front grille for better access to the top mounting points. This is optional.

What is the warranty on Mishimoto radiators?

Mishimoto offers a lifetime warranty on their radiators against manufacturing defects. Keep your receipt and register the product on their site.

Conclusion

Replacing the factory radiator with a Mishimoto aluminum unit is a straightforward upgrade that pays dividends in cooling reliability and performance. By following this guide step by step – from draining the old coolant to burping the system – you can complete the installation in a weekend with standard tools. The result is a Mustang that runs cooler under pressure, whether you are carving canyon roads or sitting in summer traffic. Remember to recycle your old coolant and radiator properly, and enjoy the peace of mind that comes with a robust, all-aluminum cooling system.

For additional support, refer to the Mishimoto Tech Support page or join the active community on Mustang6G where many owners share their install experiences.