You may have seen the recently-posted photos of the valvetrain and the cylinder head from my 2011 Prius. I am starting this thread to summarize what happened. - On the afternoon of 2/24, I observed a loud knock from the engine bay during start-up. The knock lasted several seconds. After the engine started, I also noticed stumbling for several seconds. - The next morning, 2/25, I observed the same loud knock from the engine bay during start-up. Except this time, the Check Engine Light came on. The car was scanned and I found a current P0302, as well as various pending and historical fault codes for P0302, P0300 and P0304. - Later in the afternoon, the knock happened again when I started the car to leave work. The coolant level was also 2" lower than where it previously was. At this point, I decided to stop driving the car until I had time to confirm and correct the issue. After the car was parked for two days, I removed the spark plug from cylinder #2 and performed an inspection using an inspection camera. The top of the piston was wet with liquid (coolant). For comparison, I inspected cyl #3 and it was dry. Headgasket issues are common on the Toyota 1.8L 2ZR-FE (2009+ Corolla) and 2ZR-FXE (2010-15 Prius) at high mileage. Based on my visual inspection, I decided to proceed with disassembling the engine. The game plan was to replace the headgasket (and any gaskets which were removed during the repair), resurface the cylinder head and replace the intake VVT camshaft gear (due to rattling). I am the original owner of this car. At the time of failure, the vehicle had 184,997 miles. Engine coolant had been replaced at 30K, 90K, 122K and 179K. Thermostat was replaced at 122K with a dealer unit. Engine Water Pump was replaced with an Aisin at 179K for maintenance; there were no issues. The EGR cooler and valve were cleaned at 179K (valve and pipe were cleaned once previously at 160K) and they never showed any signs of blockage. Spark Plugs had been replaced at 92k and at 179K. Here are some photos of the repair process: Cylinder Head Removed: Photo of the Engine Bay with the Cylinder Head Removed: Photo of the Camshaft Housing and Cylinder Head Removed. Yes, I am aware that I was missing one valve stem cap: My finger is pointed to the location of the head bolt that was looser than all of the other ones. Coincidentally, this is also the area where the headgasket may have failed. During reassembly, all head bolts were able to be torqued to spec w/o issue, so I am not sure why this bolt was loose: Cylinder Head after the machine shop did their work. The cylinder head was NOT warped. The shop resurfaced the head (.003" removed) to a 20rA finish, cleaned the head, did a full inspection and install the new valve stem seals I provided: Timing Cover all cleaned and ready for fresh FIPG (RTV). CRC Gasket Remover, plastic razor blades and light use of a fine wire brush was used for cleaning: Photo of the front of the engine. All cleaned: Cylinder Head cleaned and exhaust manifold re-installed with a new gasket: Cylinder Head, Camshaft Housing and Timing Cover re-installed. nthach came by and assisted; it was a lot easier to install a cylinder head w/exhaust manifold and timing cover with two people: All done: In total, I spent between 11-12 hours over the course of several days. Overall, it was not a bad job at all. There are some tricky parts to the repair, but nothing that is not DIY-able. A local dealer quoted me $4200 and a nationally-recognized hybrid specialist quoted $4800 (more if the connecting rods were bent, which is supposedly common). Book time for the job is 18-ish hours w/Engine Removal. The labor rates on the West Coast are quite high ($160/hr+) and it often not economically feasible to repair high-mileage vehicles. I ended up spending $889.85 on the parts and the machine shop work. Here is what I installed: 1) Engine Overhaul Gasket Kit - Genuine Toyota (part # 04111-37315). I used every gasket in this kit except the Rear Main Seal. This kit is awesome; it includes EVERY seal on the engine....even the dipstick tube seal and the oil cap seal. 2) Head Bolts - Genuine Toyota 3) Thermostat - Genuine Toyota 4) FIPG Black, 2 tubes - Genuine Toyota 5) Camshaft Timing Gear Assembly - Genuine Toyota (part# 13050-0T050). These have been problematic on the 2ZR-FE, not so much on the 2ZR-FXE for some reason. But I decided to install the latest revision since mine rattled occasionally. 6) 2 gals of CCI/GC Super Long Life Pink Premixed Coolant 7) Spark Plugs - Denso #3499 8) SuperTech 0w20 Dexos Synthetic and Genuine Toyota Oil Filter. Note: for the initial start-up, I filled the engine with a mix of various leftover 5w20 and 5w30 synthetic oils and a new filter. I drained this mix after the engine idled for about an hour, then the SuperTech 0w20 was installed. If you own a Toyota 1.8L with the 2ZR-FE or 2ZR-FXE, beware. There is a very good chance that you will have to do this job sometime, and if you have to pay someone, it will likely exceed the value of the car. So, I would definitely consider doing the job yourself if the engine does not burn any oil and you have not driven very much since the failure starts.