Engine Block Freeze Plug Problems

When professional mechanics are debating what the hardest job to perform as related to cooling system repairs many will immediately say the heater core. Upon further reflection, some will change their answers to a freeze plug located in between the transmission and engine block. When it comes to freeze plug problems it’s all about location. Each application will have its challenges if it becomes necessary to replace one. This article will cover the basics of the repair and point out a few special tools that can make the job easier.

Freeze or Core Plugs

Most people already know a freeze plug is used to protect the engine block from cracking in case the antifreeze water mixture freezes inside. Water expands when it freezes and instead of the block cracking the metal disc will be pushed out to allow the frozen water to expand. Although replacing one is difficult replacing the engine block is much harder and costlier.

People that make cast cylinder blocks whether it be from aluminum or iron consider these metal discs core plugs. The holes aid in the pouring and construction of all cast type cylinder blocks. After the mold cools the rough holes are machined to a particular size and a steel core plug is installed. The total number is determined by the size of the engine and design. Typically, manufacturers will have six to eight distributed equally on all sides of the block.

Common causes of Freeze Plug Problems

Unfortunately, the number one cause of a freeze plugs that begin to leak is a neglected cooling system. The pH balance can get out of whack on old coolant and turn acidic. This is especially true of the older green in color ethylene glycol products that were used up until the mid-90s. Green coolant that has turned brown has done so because it has started eating away at the inside of the cooling system.

This brownish color is rust and corrosion taken away from metal parts. On these neglected systems the lower freeze plugs tend to be most vulnerable. In this situation, it is recommended to replace all of them because even though the leak starts with one the other six or seven are most likely not far behind from leaking as well. The number one way to prevent freeze plug problems is to keep up on recommended maintenance.

Replacing Cylinder Block Plugs

The first step in the procedure is to drain the coolant. Removal of the old plug is usually done with a hammer and punch to dislodge one side of it. As one edge moves in the other comes out and can usually be grabbed and removed with a pair of pliers. They also make a special remover tool that can make the job easier on hard to access locations. The goal here is to remove it and not punch it inside.

Once removed the bore should be carefully inspected to verify there is no pitting or damage that could prevent the new part from sealing properly. Small imperfections can be buffed with crocus cloth or fine sandpaper. If heavier damage is observed the recommended procedure is to bore the hole out to a standard oversize with a matching replacement plug. This is a procedure that is most often performed with the engine removed.

Types of Plugs and Special Tools

When selecting replacement parts it’s critical to use the same type that has been removed. Modern engines have three different kinds, that include the dish and expansion variety, but the cup type is currently most common. These are installed with a flared edge facing outward and the bottom of the cup facing inside the engine block. The two most important things when installing a replacement is it needs to be driven in squarely and it must be seated fully for it to properly seal. A special tool called a freeze plug removal and installation kit is recommended for this service as it can increase the chances of success.

In conclusion, the number one way to prevent having to deal with engine block freeze plug problems is to make sure the antifreeze is fresh and properly protected. Since most people discovering this article are way past the point of prevention, I have one final piece of advice. They make a rubber expansion plug that can be used for emergencies. It fits into the hole and a center bolt squeezes the rubber outward against the cylinder block. This is only a temporary repair and fails to hold up long-term because of the high temperatures associated where the rubber meets the metal.