Leaking coolant from reservoir + passing pressure tests

I see a lot of similar problems/posts that seem to be dancing around the same unidentified "problem"... Heres a brief bulleted timeline:

1. Cold start shudder, ID'd as headgasket issue
2. Added blue devil because Im a broke/hopeful student (MISTAKE!)
   1. Fixed cold shakes for 1 year
   2. Heat stopped working
   3. Coolant started leaking through the reservoir
3. Replaced reservoir AND cap
4. Paid Toyota $2300 to replace the headgasket after it started shaking
   1. Coolant is still magically disappearing through the reservoir (there is white residue and pink liquid when I inspect). Still getting occasional overheating

The only thing that makes sense to me is that the system is overpressurized, thus causing the coolant to seep through little pores in the plastic reservoir. I have also considered that the coolant itself is overheating and "boiling off" but My OBDII/App isnt indicating above normal coolant temps...

Given that the heat isn't working worth a damn (blows ice cold air all day though), could there be a coolant clog somewhere in the system? Ive done a coolant system flush which didnt fix anything. I'd really love to try flushing the heater core with a garden hose but it doesnt seem as easy to access on the Prius v wagons...

Thanks in advance for your help and sorry for the lengthy post! Im a good historian and Ill be happy to answer any other questions to try to make sense out of this problem that seems sort of common post head gasket leak stop use...

 

Hey thanks for the reply! I appreciate the feedback. Its been about 5k miles since the HG job. It actually overheated on the way home. I took it back to Toyota the very next day and they gave it a once over and didnt seem concerned...

I actually wound up using a concentrated headgasket flushing product from Irontite after seeing some success resolving similar situations (different cars). Fingers crossed but it seems to have worked! No overheating but well wait until some more hot weather. Ill give a long term check review as well

 

Thanks for the reply! I actually used Irontite Thoro Flush and (fingers crossed) the problem seems to have resolved! No longer losing coolant and no episodes of overheating BUT I havent had any super hot days since I flushed using the Irontite...