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How to Replace Freeze Plugs in a Mustang

by Chris Stevenson

Engine freeze plugs exist on the typical automobile engine as a result of casting holes in the block or head. The holes must be incorporated into the block and head to allow escaping air during the hot-melt pour and casting process. The holes have circular shapes in varying diameter sizes, and receive steel or brass plugs to enclose the casting holes. Metal freeze plugs have pressed installation fittings, designed to hold back jacketed engine water. When freeze plugs rust or deform, they leak and drain the block or head of coolant. Replacing freeze plugs requires more labor cost than part's cost, but some procedures and tools can simplify the process.

Place the vehicle in park or neutral, depending upon your transmission type. Set the emergency brake firmly. Raise the hood and disconnect the negative battery cable with a socket and wrench. Use a floor jack to lift the vehicle front end and place two jack stands under the frame, extended at full height. Raise the rear of the vehicle and place two jack stands under the frame at full height. Place a drain pan under the radiator.

Use pliers to to loosen the radiator petcock valve and let the coolant drain into the pan. Remove the radiator cap to facilitate a faster drain. Take a shop light under the vehicle and locate the leaking freeze plug.

Refer to your owner's manual for all of your freeze plug locations, if you need to replace all of them. To remove a freeze plug out in the open on the side of the engine block, place a long-handled chisel on the lip of the plug and strike it with a hammer. Strike it until the plug twists and bevels outward. Remove the plug with a pair of pliers. For a freeze plug that sits behind a motor mount, remove the motor mount bolt and nut with a socket.

Place a floor jack under the oil pan, with a block of wood on the lifting spoon. Raise the engine for enough clearance to use the hammer and chisel, but not high enough to bind the exhaust system or twist the transmission. After removal of the plug, use a wire brush to thoroughly clean the casting hole. Wipe it clean with a rag.

Place a dab of silicone on the edge of a new freeze plug and squarely wedge it in the casting hole. Use a hammer and back of a large socket to tap the metal freeze plug into the casting hole until it seats. If you must use a rubber expansion plug, lubricate the edge of the plug with some silicone.

Place the freeze plug into the casting hole and tap it into its seat with a hammer. Use a socket to turn the expansion plug nut clockwise until the rubber plug pressure fits solidly in the hole. Replace all freeze plugs in this fashion, using either the metal-type plugs, or the rubber expansion-type for hard to reach areas. If you removed a motor mount bolt, lower the floor jack and align the motor mount hole. Insert the bolt and nut and tighten it with a socket.

Use pliers to close the radiator petcock valve. Refill the radiator with coolant to the proper level and seal the radiator cap. Use the floor jack to raise the vehicle and remove the front and rear jack stands. Reconnect the negative battery cable with a socket. Start the engine and let it warm up. Check for leaks at the new freeze plug location.

Tip

  • To replace a freeze plug on the end of a cylinder head, remove the component blocking access to it. This could be the smog pump, alternator, power steering pump or air conditioning compressor. You can remove the component bracket bolts with a socket and shift the component aside, including the air conditioning compressor.

Items you will need

About the Author

Chris Stevenson has been writing since 1988. His automotive vocation has spanned more than 35 years and he authored the auto repair manual "Auto Repair Shams and Scams" in 1990. Stevenson holds a P.D.S Toyota certificate, ASE brake certification, Clean Air Act certification and a California smog license.

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