2013 Prius Misfire

I have been soaking it in a bucket of hot water and soap solution for a day or so, replacing the solution periodically (working around other obligations) and it seems to be helping. At least now the solution will drain through although slower than I think it should.

Head gasket, timing chain, etc. parts should be delivered today so I am hoping to have the cooler ready to reinstall tomorrow or the next day depending on how quickly I get that far on assembly.

I suspected that hot EGR was not a good idea so I am not surprised that is not a path anyone should take. I think that a plugged cooler is different than the typical EGR delete by un-pluging the valve in part because I suspect when the system detects the EGR malfunction it changes the engine calibration.

I suspect that the head gasket leak was raising coolant temperatures, just not enough to trigger the overheat warning further accelerating the failure. I had been atributing the pressure in the coolant system after shut down to normal system pressure but after reflection suspect that the head gasket leak was adding pressure to the cooling system. I believe the head gasket failure was basically allowing combustion pressure to leak into the cooling system during engine operation, then allowing coolant to enter the combustion chamber when the engine was off. Each time the engine started (either cold or during normal hydrid off-on cycling) the engine would misfire due to the coolant in that cylinder. Not enough coolant to cause white smoke or leak down into the engine oil but enough to cause the misfire.