How to Install a Radiator on a 1965-1966 Mustang

How to Install a Radiator on a 1965-1966 Mustang

Last Updated December 6, 2023 | Bill Tumas

Whether your old radiator won’t hold pressure, leaks constantly, or you just need something better to accommodate a larger engine, there are lots of reasons to replace it. Follow the steps below to learn how to install a new radiator on your 1965-1966 Mustang in about an hour and a half.

Step-by-Step Instructions

In the steps below, we’ll show you how to install the ACP MaxCore Radiator. It’s a direct factory replacement, but it has larger aluminum cores that help it dissipate heat better. We’ll be able to reuse the factory hardware to bolt it into its original location. It also maintains the factory connection locations for the automatic transmission cooler.

Required Tools:

  • Slotted Screwdriver
  • 3/8" Ratchet
  • 1/2" Socket

Step 1: Make Sure Radiator Is Cold

Wait for the radiator to get cold before you drain the fluid. If it’s hot, it might still be under pressure and could cause harm or injury.

Hand hovering over radiator to sense whether cold or hot

Step 2: Drain Radiator Fluid

Place a bucket or container below your radiator. Then, either remove the lower radiator hose or open the petcock at the bottom of the radiator to drain the coolant.

Coolant draining out of radiator into bucket

Step 3: Remove Upper Radiator Hose

Unscrew the hose clamp on the upper radiator hose, slide it down, and pull the hose off the radiator. Tuck the hose out of the way for now.

Sliding hose clamp off upper radiator hose to remove

Step 4: Remove Transmission Lines

Once the fluid is completely drained, remove the two transmission lines at the bottom of the radiator. There should be one on each side. Use your screwdriver to loosen the hose clamps and remove the hose.

Hand pulling transmission line off bottom of radiator once hose clamp is loosened

Pro Tip: If your transmission lines or radiator hoses are worn and brittle, now’s a good time to replace them.

Step 5: Remove Radiator Bolts

Use your 1/2" socket to remove the four radiator bolts. There are two on each side at the top and bottom of the radiator. Hold on to the bolts for later.

Using socket to remove radiator bolts from radiator

Step 6: Lift Radiator Out

Once the bolts are out, grab the radiator on each side and pull it straight up to remove it from the engine bay.

Using both hands to gently lift radiator up and out of engine bay

Step 7: Replace Lower Radiator Hose (Optional)

If you’re not replacing the lower radiator hose, you can skip this step. Otherwise, with the radiator out of the way, loosen the hose clamp and remove the lower radiator hose from the water pump. Place hose clamps on the new hose and slide it onto the water pump before tightening.

Placing new lower radiator hose on water pump

Step 8: Remove Radiator Fan (Optional)

If your radiator is thicker than the original, you may need to remove the radiator fan to get it to fit. To remove the fan, simply unscrew the four bolts in the center of the fan blade using your 1/2" socket and slide the fan off.

Pulling radiator fan off spacer once four bolts have been removed

Step 9: Install New Radiator

Slide the new radiator into place and use the four bolts from Step 5 to secure it.

Installing new radiator using the existing bolts

Step 10: Check Fan Spacer (Optional)

Make sure there will be enough space for the fan between the water pump pulley and the new radiator. If you need more space, you’ll need to replace the fan spacer with a shorter one. To remove the fan spacer, gently pry it off the pulley using your screwdriver.

Removing fan spacer with screwdriver

Step 11: Reinstall Transmission Line Fittings

You can reuse the original transmission line fittings from your old radiator or install new ones. Apply some sealant on the threads and carefully tighten them down with your 3/8" ratchet.

Original transmission line fittings reinstalled at bottom of radiator

Step 12: Reinstall Transmission Lines

Slide the transmission lines back onto their fittings. Tighten the hose clamps to secure them.

Sliding transmission line back onto fitting before tightening hose clamp

Step 13: Reattach Lower and Upper Radiator Hoses

Slide the lower and upper radiator hoses back onto the radiator and tighten the hose clamps.

Repositioning clamp on upper radiator hose

Step 14: Install Overflow Hose

Slide the overflow hose onto the nipple on the side of the neck. Then, slide the hose between the two clamps on the side of the radiator. Lightly press down on the clips to secure it in place.

Consider installing a radiator overflow tank if you're having trouble with coolant overflow.

Sliding overflow hose between clamps on side of radiator

Step 15: Install Fan Spacer and Cooling Fan (Optional)

If you had to choose a smaller fan spacer, attach it to the water pump pulley. Reattach the cooling fan by sliding it onto the spacer and tightening down the four bolts from Step 8.

Water pump pulley where fan spacer and cooling fan will attach to

Step 16: Add Coolant and Attach Radiator Cap

Refill your radiator with coolant and seal it up with your radiator cap.

Placing radiator cap on radiator neck

Considerations for Your Radiator Install

Your installation may be slightly different based on the radiator and accessory components you choose. Whether you’re sticking with factory replacements or upgrading, this guide should give you a basic understanding of the overall process. Just be sure to follow any instructions from the manufacturer of the parts you buy. If you want to learn more about your Mustang's radiator, check out our radiator vs intercooler guide.

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Please Note: This guide is a tool to help you install parts on your vehicle. If you don’t feel confident performing this installation on your own, please have a professional install the parts for you.

This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about CJ's editorial standards and guidelines.