When i start my 136k miles 2010 Prius, it starts fine but i can hear a continuous low volume knocking. After working for about 20minutes switching between Hybrid and Combustion Engine a couple of times, it switches to combustion, increases the rpm and doesn't switch back to Hybrid. Coolant temperature would increase to 90-95 degree celsius and i see it boiling in the coolant tank. When i off the car, the combustion engine shakes heavily. Cylinder 3 and 4 misfire code come up sometimes. CONS: Car at 136000miles, Head gasket not yet changed. Changed EGR valve Changed Fuel injectors Cleaned egr cooler and intake manifold. PROS: I am not losing coolant. Checked cylinder valve via Borescope camera through spark plug hole and can see exhaust valves with heavy brownish build up. Engine cylinders has some burn/rust looking surface and like an oil in Cylinder 4. (see attached pictures) I want to know if this issue can be caused by a failed head gasket and if the cylinder build up is from same or something else.
If Your head gasket failed, bubbles in the coolant are from exhaust gasses in the coolant system. Borescope down the spark plug holes look at the tops of the cylinders. You might see a clean top on one which is a clear indication of a failed head gasket, maybe not since you are not losing coolant.
