Published on December 08, 2025 Author TUCKER HARRIS Share article Facebook 0 Twitter 0 Mail 0 Firepunk’s Fix for Failing Cummins Freeze Plugs Firepunk Diesel’s Solution to Weak Factory Cummins Freeze Plugs Freeze plugs—also known as core plugs or expansion plugs—serve a vital role in sealing the casting holes in your 5.9L 12V Cummins engine block. Over time, these steel plugs can corrode and begin to leak—especially in high-mileage engines or trucks that have seen years of exposure to coolant OR high pressure in the coolant jackets from big power. Replacing them isn’t the easiest thing to do, but it’s also not the hardest job for hands-on diesel enthusiasts. Drain the Cooling System Begin by allowing the engine to cool completely. Open the radiator drain and remove the block drain plug if equipped. Catch all the old coolant in a drain pan. Removing the thermostat housing or heater hose can help the system drain faster. In our case, our engine is in a frame with no body or charger on this specific install. Remove the Old Plug Use a punch or screwdriver to tap one side of the old freeze plug inward. This will pivot it into the bore so you can grab the other edge with pliers and pull it out. Take care not to gouge the block surface—cleanliness and smooth sealing surfaces are key to a tight seal. Clean the Bore Scrub the bore lightly with a red Scotch-Brite pad until it’s smooth and free of rust and/or debris. Wipe the area clean with brake cleaner or solvent to remove any residue. Install the New Plugs Partially assemble the freeze plug, run the screw into the mounting block a few threads, and set it into the hole in the engine. Align the plug squarely in the bore and tighten down the Allen bolt, making sure the O-ring on the plug itself isn’t getting pinched. Drive it in until it sits just below flush with the block surface. Subscribe Our Weekly Newsletter Refill and Test Reinstall any components you removed, then refill the cooling system. Start the engine and check for leaks while it warms up to operating temperature. Reinspect the area after a short drive to ensure a solid, leak-free seal. Thanks for being with us through another tech article here at Diesel World! This one covers something that a lot of people are scared of doing—including us. The job ended up being one of the easier installs we’ve done this year—so don’t listen to the rumors about changing freeze plugs on your Cummins truck. Happy wrenching! Total 0 Shares Share 0 Tweet 0 Pin it 0 Share 0
![](https://ad.ipredictive.com/d/track/event?upid=111299&url="https://www.dieselworldmag.com"&cache_buster=1765208713&ps=1)