Your engine block is full of holes to the outside world. These holes are part of the casting process, where the sand is poured out of the completed block casting. Most of these holes are in the cavity that is used by the cooling system, known as the water jackets. You can’t just leave those open to the atmosphere, all the coolant would pour out. The solution is what we call freeze plugs.
They are called freeze plugs because they are a defense item. Should the water in the engine block freeze, the idea is that the plugs would pop out before the block cracks. Sometimes they work, sometimes they don’t. Freeze plugs typically are installed and forgotten about, but when you have problem, they can be a thorn in your side. Installing freeze plugs is not hard, but there are some complications that arise. Some of the freeze plugs are easy to reach, but there are some that are impossible to reach with the engine in the vehicle. Take a typical small block Chevy, there are three easy to reach plugs on the sides of the block and a couple of the front, but there are two plugs on the back of the block that you can’t reach without removing the engine, and a couple on the front that require tearing down the front of the engine.
The most common issues with freeze plugs are freezing and corrosion. If the temperature drops below the protection level of the antifreeze in the water, then you run the risk of the water freezing. When that happens, the water expands. If you are lucky, it will only push out a freeze plug or two. Once the water melts, the coolant will start to leak from the freeze plug.
Corrosion failure is a bit different. There are three types of freeze plugs: brass, rubber (expanding), and steel. Brass plugs don’t corrode, which is why they are the preferred type. Steel plugs on the other hand, rust pretty easily. Over time, the corrosion will break down the seal, allowing the plug to leak. Rubber plugs, which are commonly used for quick repairs, breakdown over time from the heat cycles. They have to be replaced as soon as they start leaking.
Freeze plugs come in many different sizes, and your engine will have multiple sizes, some engines have 10 or more plugs. You can purchase a complete freeze plug kit, or you can buy individual plugs if you need to only replace one or two. We highly recommend brass plugs for a lasting repair.
Removing an old freeze plug requires a punch and a hammer. Some people use screwdrivers, but we all know that screwdrivers are for screws, nothing more. Use the punch on one lip of the plug, and then hit it with the hammer until it folds over. Once it is folded over, you can use pliers or vice grips to pull it out.
It is always a good idea to use a little sandpaper or a Scotch-Brite™ pad to clean up the hole in the block. Inspect it and look for signs of cracks. You just want to knock off any loose rust or sealant.
Clean the surface with some brake cleaner and wipe dry. Then prep the plug with some Permatex Form-A-Gasket #1 sealant. This product is designed for freeze plugs and other press-fit applications, as well as gaskets. Just a thin coating is all you need. You don’t have to use it, but you have a better seal if you do.
Align the plug into the hole and press it in by hand. You should be able to get it to hold by hand.
Next, use a bearing driver and a hammer to drive the plug into the hole. You want to drive on the outside of the plug, not the inside.
Once the plug is flush with the block, the job is done.
Replacing freeze plugs is not hard, but getting to them can be really tough with the engine in the vehicle. If you can’t get the plug replaced in the car, then you may need to visit your local NAPA AutoCare Center for assistance.
Check out all the engine parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to install freeze plugs, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.