Freeze Plug (Everything To know)

Freeze plugs are vital components in a vehicle that protect an automotive engine from cold-related damage.

Freeze plugs are essential, and you must check them regularly. But, unfortunately, most drivers never do so.

Freeze plugs should last over 100,000 miles before going bad, but they eventually wear out.

Failed engine Freeze plugs can lead to serious and extreme damage to the vehicle’s engine and its cooling system, which are very difficult and expensive to fix.

In this article, you are going to learn everything you need to know about your vehicle’s freeze plug, How it works, what makes it go bad, how you can fix it, and more.

Before now, ordinary water was used as a coolant for combustion engines. Water is effective at cooling the combustion engines.

However, water freezes at a very low temperature, become solid and expands. This substantial expansion can lead to the destruction of the engine block and radiator cooling pipes, leading to the engine’s freeze plugs pushing out.

Presently, cars no longer use water as a coolant but a combination of water and antifreeze.

Nevertheless, it would help if you still made efforts to protect your engine’s freeze plugs from failing because, despite the antifreeze, freezing is inevitable.

What Does a Freeze Plug Do

What Does a Freeze Plug Do

In the past, freeze plugs were only used to protect the engine from damages related to low-temperature freezing.

Whenever the coolant within an engine freezes, it will eventually crack the engine block.

The expansion of water during freezing creates a lot of pressure, so the engine block cracks as it freezes. The freeze plugs prevent this damage.

The sand casting method is used for Durability and strength during engine block production. Here an engine mound is created and pressed into the sand.

In this process, the engine block is imprinted in the sand, and then molten iron is used to mold it into the final form.

You will notice some cylinders on the engine block. The freeze plugs are used to close these holes.

One of the major reasons freeze plugs fail is that they are mostly made out of thin strips of metal, in most cases galvanized steel that corrodes and rust over time.

Antifreeze solutions have greatly reduced the effects of freezing in recent times, which causes the freeze plugs to expand, but not much is known about antifreeze’s use in preventing rusting.

Some people use brass freeze plugs instead of steel freeze plugs. Brass freeze plugs will hardly fail because of their rust resistance, but they are costly, and not everyone can afford them.

Also Read: Car Leaking Antifreeze When Parked (Causes & Fixes)

How Does a Freeze Plugs Fail

Freezing is the reason why freeze plugs fail. The freeze plugs were created to protect the engine block from cracks whenever coolants freeze and expand.

However, the freeze plugs do not allow the pressure from the coolant expansion to affect the engine block by allowing the frozen coolant to expand out the plugs’ passages.

Freeze plugs can pop out of their passages if the expansion pressure is too much; when this happens, the freeze plugs are said to have failed.

In addition, the unplugged freeze plugs will create a space where coolant can leak out of your cooling system. The constant coolant leak from this unsealed passage on your engine block will eventually lead to your engine overheating.

Freeze Plugs Leak

Freeze Plugs Leak

Freeze plug leaks are possible when your cooling system freezes or approaches freezing. When a leaky freeze plug is discovered, it is wise to check your engine for damages right away.

Also, check the mixture ratio of your antifreeze and make sure it corresponds to the freezing point.

Another reason freeze plugs leak is the thermal strain of the cooling and heating cycles of the engine.

Freeze plug leaks have been a rare case in recent times because of minimal or no movement of the freeze plugs due to the use of antifreeze.

Nowadays, the freeze plugs act more like a metallic seal in the engine. The freeze plugs are hammered into the passages, and as they slide in, the metal freeze plug conforms to the plughole creating a great seal.

Despite freeze plugs being great seals, freeze plug leaks are still inevitable.

Learn more about freeze plug leak by checking out our guide on Freeze Plug Leak (Causes & Fix)

Symptoms of a Bad Freeze Plug

If you notice any of these signs, it probably means your freeze plug has gone bad.

  1. Noticing the formation of bubbles in the coolant system is a sign of a problem, and you should check the coolant reservoir.
  2. A strong smell of heated coolant is another symptom that could mean the freeze plug has gone bad, and the coolant is leaking out from your engine.
  3. White exhaust smoke is also a likely symptom of a blown freeze plug.
  4. The constant overheating of the engine is another sign that most of the coolant has leaked.
  5. If you do not see any visible leaks even when you notice a low coolant level in the coolant reservoir, it could mean the freeze plug has gone bad.
  6. Struggling to accelerate could also be another sign of coolant leakage.
  7. Check your coolant reservoir if you notice milky discoloration on your oil cap because it could also mean a blown plug.
  8. Engine misfiring is another sign that your freeze plug could be bad.

Symptoms of a Bad Freeze Plug

How to Replace Freeze Plugs

Step 1

Drain out the mixture of antifreeze and coolant from your car’s cooling system before removing the freeze plug, so it doesn’t spill.

Next, slide under the vehicle and unlock the petcock to drain the coolant. The petcock is a little valve with a handle located on the bottom of the vehicle’s radiator.

Remember to place a bucket under the petcock to collect the coolant. Then you can lose the petcock and allow the coolant to drain out. You could use a plier if it is a little tight.

Step 2

Remove the components that restrict free access to the freeze plugs. These parts vary in different vehicles, but some of the other parts you might need to remove include; the alternator, intake manifold, exhaust manifold, etc.

Step 3

The freeze plug can be broken by punching it with a sharp object.

Next, you use a hammer to tap the punch lightly. Continue tapping it until the freeze plug breaks.

You may need to repeat this several times to break the freeze plug completely. Be careful so that you don’t scratch the engine while doing this.

Step 4

Once you have removed the freeze plug, gently grasp it with the pliers to avoid pushing it into the engine block.

Next, pull out the freeze plug, although this might be difficult. Slant the plug to the side before pulling it out, so it’s easier.

Step 5

It is important to clean the freeze plug hole thoroughly. You can use a degreaser and some rags. If there is any leftover grease, the new plug will not seal properly.

Step 6

Carefully insert the new freeze plug in the hole. This procedure is done by placing a socket wrench of the corresponding size over the freeze plug to protect it.

Next, gently tap the socket wrench with the hammer until the plug enters the hole completely and sits.

Then, put loc-tite around the entire outer edge of the plug to seal it in place. You will now need to replace the parts you removed to get to the freeze plugs.

After everything is back together, tighten up the petcock. After tightening the petcock, add the antifreeze that you previously drained.

Check out this video for more tips on replacing freeze plugsĀ 

Freeze Plug Replacement Cost

The costs of replacing your freeze plugs vary with the type of vehicle you drive.

Another factor determining the cost of repairing freeze plug leaks is the total number of freeze plugs and their locations on the engine. Finally, the auto mechanic/dealership you use to perform the repair.

A freeze plug located at a very accessible place on the engine could cost from $200 to $400.

In comparison, a freeze plug that is more difficult to access can cost from $900 to above $1,800 because the mechanic might need to lift the engine and transmission or remove most of the engine parts to gain access.

Frequently Asked Questions About Freeze Plug

What Does a Freeze Plug Do?

Freeze plugs protect engines from frost-related damages. For example, a frozen coolant will expand and cause a crack on an engine block. However, Freeze plugs do not allow these cracks to occur but rather allow the freezing water to expand out the plugs’ passages. Therefore, if a freeze plug fails, it is necessary to replace it immediately.

What Causes a Freeze Plug to Pop Out?

The freeze plug pops due to the expansion pressure from the freezing coolant. If this coolant freezes inside your engine block, it will crack the block and destroy the motor. Freeze plugs will “pop out” and prevent this situation from happening.

Can You Replace Freeze Plugs Without Removing the Engine?

Yes! You can replace freeze plugs without removing the engine. Whether the freeze plug is made of metal or plastic, as done in recent times, they are all inserted into the core bores by friction fitting. The core plugs will eventually leak over time due to corrosion from the cooling water system. Once the plugs leak, you must remove them carefully without damaging the engine block.

Can You Drive With a Leaking Freeze Plug?

You could drive with a bad freeze plug when there is no other option. This action is not safe, but if you must, you have to keep your engine coolant level always full and keep enough reserve in the car, which will protect your engine from overheating. With this, you can limp your vehicle along with a leaking freeze plug, although it is highly not recommended.

Can Leaking Freeze Plug Cause Overheating?

When you allow your freeze plug to leak for too long without repairs, your engine’s coolant could eventually reduce to a level where it can no longer effectively cool your engine, leading to overheating, which can cause extensive damage.

How Often Do Freeze Plugs Need to Be Replaced?

There is no need to wait until the freeze plugs all go bad. After every three years or 60,000 miles, replacing your old freeze plugs with new ones is advisable. If you use plain water as your coolant without good rust inhibitors, rust will attack the freeze plugs sooner as it is the weakest link in the engine block.

How Much Is a Freezer Plug?

A freeze plug located at a very accessible place on the engine could cost from $200 to $400, while a freeze plug that is more difficult to access can cost from $900 to above $1,800 because the mechanic might need to lift the engine and transmission.

What Causes Leaky Freeze Plugs?

In most cases, the expansion of water in the engine block is due to freezing. As a result, the freeze plugs will pop out, relieving the freezing water pressure and partially draining your cooling system. However, another reason freeze plugs leak is the thermal strain of the cooling and heating cycles of the engine.

How Long Does It Take to Change a Freeze Plug?

The average labor time to change a freeze plug is between 30mins to 1 hour for each freeze plug if done by a professional mechanic.


Freeze plugs are an essential part of the engine block. They are usually seen as shallow depressions on the engine block.

Their purpose is to protect the engine block from damage due to coolant expansion from freezing. The freeze plugs allow the frozen coolant to expand by sliding out, and in a worst-case scenario, they “pop out.”

Antifreeze or engine block heaters are available in modern designs, so you don’t have to worry about leaking freeze plugs. However, freeze plugs can rust over time, still leading to leaks.

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