2017 Prius 3 heat exchanger bypass?

New to the forums 2017 Toyota Prius 3 owned since new change oil and check fluid levels on regular cadence. I recently crossed the 300k line and started seeing issues so i came and read about a heat exchanger bypass due to the recent issues. White smoke, code P148-F00, and low coolant.

I ordered the gates hose as suggested and installed it. I filled up the coolant and once up to temp topped it off. I allowed it to idle with cap off and topped off multiple times back to full to remove all air from system. I test drove 4 miles and came back and it was at low again. I topped off and allowed it to idle 30 minutes. I test drove again same 4 miles and came back it was at low. I loosened cap to release pressure and noticed it was at full.

The white smoke seems to have subsided. It doesn't smell of antifreeze from the exhaust anymore. It doesn't stutter when transitioning from battery to combustion as it had started to at idle. There's no milky residue in the oil. Generally a blown head gasket you'll remain to see the white smoke on exhaust side, or you'll see the water back up on intake side, or get milky oil.

Can a defective cap build excess pressure on the over flow causing it to not allow water back into overflow? I drive this car 3k miles most weeks and want to ensure I'm safe to do so. Thanks in advance it's still my first hybrid all these years later and I'm still learning.

 

Coolant temp light came on while driving. It instantly went back out and did not come back on. I drive it the 15 minutes home and checked coolant and it was low. This was the first time in my 7 years owning it that it was ever low.

The following day same issue. Coolant light came on and went back out. I arrived at home and again it was low.

I did do the bypass for heat exchanger to rule it out. It seemed to fix the issue.

I drove it 10 minutes and checked coolant it was fine. I drove it 1 hour checked coolant it was fine. I drove it 3 hours checked coolant it was fine. I drove it 8 hours and checked coolant it was slightly low. I checked it the flooring morning and it was still slightly low. I added around 1 cup of coolant and drove it around 5 hours. It was again low the following morning I added around 2 cups of coolant. The following 2 days I added the same amount each morning. I added uv dye to the coolant system and I see it around outside of overflow.

I did a gas engine combustion leak test and got a slight change in color from the test fluid indicating a blown head gasket.

Current issue it seems like you have to remove the engine to swap a head gasket.

 

I took some time away and replaced the head gasket from direction of a friend. My coolant issues seem to be gone but now I have an intermittent idle issue along with a p0171-00 code. I also get a random P0100-64.