Am changing both coolant loops but so far just the engine. I am using SLLC as in the new model Prius, not the original LLC. SLLC is sold pre-diluted for about $19/gallon. According to the spec, 5.2 US quarts (4.9 L) are required. The radiator drain plug is as described in the tech manual, but the engine drain plug is not. To access that one, put the front end up on at least 4" of lift and crawl under. Between the engine and the firewall, look up for a 10 mm bolt and a metal drain tube on the engine. I'd call it about 6 " straight up from the vibration damper on the right drive shaft. Picture later. First turn on the cabin heater and remove the radiator cap. Now drain each drain into a pan and close them. Empty the overflow reservoir as well. From all these I collected 4.1 L, not 4.9, even though the overflow was initially at the top line. Uncertain if this means an incomplete drain, or if the spec is wrong (hey it could happen). Now drains closed, begin to add new coolant via the radiator cap hole. Initially I could only get 2.9 L in, so obviously there was air to be cleared from the system. The stated way to do this is to start the engine and run it until the radiator fan starts, then shut down. When cool enough to open the radiator cap, fill to the top and close. Repeat the heat/cool/fill cycle. I did many repetitions, adding only small amounts of coolant each time. If you have access to Graham Davies miniscanner or similar you can watch the engine coolant temperature rise. If not, you can time how long it takes for the rad fan to kick in each time. That time increases through these cycles, which indicates that one is making progress. Adding coolant each time does, as well. But again many repetitions are needed. I now consider this a full-day job (having started yesterday noon). It took me at least 15 reps before the cabin air 'blew hot', the first indication that air was getting displaced from the heater core. Have now added a total of 3.45 L new coolant, including the overflow res. being filled. So I am still 0.65 L behind according to what I removed, or 1.45 L according to the spec. I reckon it is safe to drive this way, but feel better being able to monitor the coolant temp en route. Would be wise to shut down, cool, and try to add more if it gets near 100 oC. When everything is working correctly, additions can be made to the overflow tank w/o reopening the system. The tech manual says you may need to get into 'inspection mode' to keep the engine running during the heatups, but I have not found that to be the case. Squishing the accel pedal does it for me. On some cycles I get bored, so I force-charge the HV battery. Everyone says that the inverter coolant loop is trickier, but it has bleed valves so there is at least a mechanism to remove air. We'll see. I had run the LLC coolant for 44k miles (spec is 30 k), but its appearance is quite good. The only particles appear to be little black bits that I attribute to erosion from the rubber hoses. Now equipped with SLLC, my replacement cycle ought to be 50k miles. Given the time required for this process and the cleanliness of the coolant, don't be surprised if I stretch that. Naturally after this, it is good to check for drips under the drain valves for a few days at least, and monitor the level of the overflow tank. Toyota does not charge huge $$ for this, so maybe they have a trick. I think it might be nice to pump coolant up into the engine drain valve until the radiator wants to overflow.