On the list of common things that fail on 7.3’s, freeze plugs are fairly low; however, as these trucks grow in age, they’re becoming more and more common. Failure can occur in many ways, but it is generally due to corrosion. The OE plugs were typically made from stamped steel with a zinc (or similar) coating to protect against corrosion. These plugs, under ideal conditions, can last the life of the engine, but when coolant maintenance is neglected, they corrode significantly faster than when coolant maintenance is kept up.

Coolant contains corrosion inhibitors. Over time, these inhibitors break down. If the coolant isn't changed at recommended intervals, it can become acidic and start eating away at the metallic components of the cooling system, including the steel freeze plugs. Because of this, most plugs will look perfect (or ok, at least) from the outside but will leak from small pin holes due to the corrosion happening on the other side, within the coolant gallery.

Replacing them is fairly straightforward, the biggest issue is not to lose the plug inside the block (or head) when it comes free. There are many ways to do this, the most common and well-known being the following:

1. Drain the coolant from the block to reduce mess.
2. Use a chisel or punch, and hammer, to rotate the plug within its bore. This can be done by pushing/hammering in on one side only until the opposite side pushes outward. Care must be taken here not to push the plug into the block (or head). Go slow.
3. Once the plug has rotated to the point where one side is accessible enough to get a set of pliers on it, the plug should pull out easily.
4. Now for the install. First, apply a thin coat of sealant to the plug bore on the block (many exist, we like Loctite 680 or Permatex Aviation Form-A-Gasket).
5. Now we need a tool to install the new plug. Specialty tools do exist, but a socket matched closely to the inside diameter of the new plug works just fine in a pinch. Place the plug onto the socket and drive the plug into the block until it is flush with the bore. Go no further than this, or you’ll risk pushing the plug into the coolant gallery.
6. Refill the system, bring the engine up to temp, and check for leaks. No leaks? You’re good to go.

Many will do added things to ensure not losing a plug in the block (or head). Some will drill a hole and install a screw, they’ll hold onto this screw while hammering on one side of the plug. We’ve even heard of people cutting a slot in the old plug and inserting a screwdriver into it, and prying out the plug that way. Whatever you’re more comfortable with is likely fine. Just make sure if you go with one of these latter options, don’t drill or cut too far into the plug where you damage the sealing surface, or damage what's behind the plug (most often, the cylinder wall itself).

Many different aftermarket options do exist for the plugs themselves. Some will thread the block and insert threaded plugs. Now, the argument against that process is somewhat flawed. Most believe that the freeze plugs are only there to guard against the block cracking under extreme cold temperatures, where the coolant within it freezes. The holes in the block that the plugs reside in were in fact put there to aid in the removal of sand used in the casting process. The use of the plugs to prevent block cracking was just a happy accident, and not one that always works as intended. Long story short, threaded plugs aren’t as bad as many think, although they’re overkill for 99% of us.

Stainless or brass plugs. Stainless definitely corrodes less than its steel brethren, although it can be harder to install and seal properly, as stainless is a harder material. Brass should corrode less quickly as well, and many will attest to that, but many will also argue brass degrades just as fast, or faster than steel plugs. We’re not going to go into the metallurgy here, as to which metals degrade/corrode the fastest, as it really doesn’t matter. 

In the end, standard coated steel plugs have been effective for decades, with poor coolant maintenance being their most common downfall. Even with poor coolant maintenance, steel plugs last a very long time. Long story short, replace your plugs with quality steel-coated ones (found HERE and HERE for 7.3's), stay on top of your coolant maintenance, and you should be good to go for decades to come.