*For Informational Purposes Only here, Names and such withheld due to privacy but this car came into our shop this week and I wanted to share some pics with the community in hopes it would help someone somewhere somehow* Gen 4 Fans, viewer discretion advised. Customer's 17' Prius Prime with 150,000 miles came in for a cold start rattle and coolant loss. Originally thought to be the dreaded heat exchanger valve that stuck (negative lucky for him, HVAC system pressurized and held over night), welds were also okay. Moved to the dead or dying water pump theory (with 150k miles it was close and could have run a few more thousand miles but advisable to change now due to the high labor hours for Gen 4 Water Pump swap we decided to do this now and likely small contribution to this issue). So 2 strikes as to cause..leading to simple coolant not being changed (likely ever) and non warm up situation with very aggressive driving habits along with crappy Toyota gasket materials as you can see. Same thing as a Gen 3 here. EGR not an issue and clean. Not sure a 100k water pump and coolant flush would have helped here. With that being said...look at those pistons! CLEAN @ 150k miles...yep, still Gen 4 is King with the EGR routing getting burnt off by the cat. At 150k miles on a Gen 3, the tops of the pistons are charcoal even on a healthy engine. Unbelievable! Now FEL-PRO reps are you listening? Manufacture a Gen 4 Head gasket like yesterday! Car now runs great back to it's old self, hopefully the owner starts driving it like a Hybrid Unfortunately for us Gen 4 in Gen 3 car guys, we're going to muck up the pistons with some mileage with that Gen 3 EGR on them, but ..oh well.