For a writeup! 7.3 Superduty Coolant Flush Writeup Tools/Supplies needed: ¼ “drive ratchet + short ¼’’ extension Socket/Extension for thermostat housing (5/16” I believe) 5/8 “Tee” for heater hose Channel locks, pliers Bottle of radiator flush New coolant filter (if equipped) Distilled Water Coolant My Superduty was coming close to 70,000 miles and I figured I’d switch to an Extended Life Coolant, and also not knowing how old the green stuff was. I setup an entire day on the weekend with the help of a buddy to flush her out. I got the old coolant in the truck good and hot on a drive before beginning flushing my system. I let it cool for a few minutes while I gathered everything. You can either drain the radiator by the drain petcock on the drivers side, which on my PSD the plastic nut that opens it broke off, so I was now draining everything from the lower radiator hose. Take caution when working with hot coolant. The flushing begins: I drained, and refilled the radiator with hot tap water until it was close to the top of the degas bottle, since it would burp air it’d go down. I started it up, let the truck run for a little bit until I saw a good green tint flowing into the overflow bottle. I left the overflow pressure cap on, but loose so it could burp the air. I ran the defrosters on high too. Occasionally I would run it at a higher idle RPM just to aid in the trapped air, I didn’t have any issues though. You can also pull the thermostat out of the housing while you are flushing, and be careful with adding cold water to a hot engine. You might notice small amounts of sand, that’s normal casting sand. I didn’t see too much since I happened to have a bypass coolant filter already working for the past 4 months. I repeated this same process once more. The third flush I added two bottles of Zerex radiator flush, let it idle for a few minutes and took a good drive down the road when I was sure nothing was leaking. Drained everything at the lower radiator hose again, and connected the 5/8 flushing tee to the heater core hose that is visible on the front left of the engine heading towards the firewall, it’s right near the oil fill cap and has protective heat/wire shielding on parts of it. Cut it, and insert the “Tee”. The NAPA flushing tee I bought had a block off cap included so you can opt to leave it permanently on the heater hose, which I chose to do. I used hot tap water and ran it through the heater core hose while left the lower radiator hose disconnected still. I let it run for about 2 minutes. I then used the ¼ ratchet and small extension to get to the block drain plugs, one plug is right near the oil filter housing on the drivers side, the passenger side plug is a little more tricky to get to, it’s almost right above the starter. It helps to have more than 1 person during this part, just to guide you while looking in from the fender well for the first time while you’re underneath. Let the block drain out, you should see pretty clear colored water coming out by now. I also used some compressed air and blew into the flushing tee to blow out the remaining water. I believe the block drain is an important step, you get about 2 gallons out of the block. At this point, I was happy with how good removing the green stuff was at by now, and just reinstalled the block plugs, got the flushing tee capped off. At the same time, I replaced my lower radiator hose, used Diesel Sites thermostat housing and their 203 degree thermostat. I installed a new coolant filter at this point as well. I didn’t opt to flush with distilled water, even though I had a few gallons. I bought pre-mix CAT ELC, so it didn’t even get used. I think around 8 gallons filled me up to the correct level on the degas bottle. Refill properly, and you’re done. It took a total of about 3 and a half hours. Don’t forget to dispose of the old coolant properly!