If you are getting pressure in the coolant, it does sound like a head gasket issue. Do me a favor. Take a look through this link and let me know if you see things that mirror what you have experienced.
As far as the Blue Devil, I have never used it. However, I know people that have, and it worked as designed. The only issue is how long it will last. It isn't a permanent fix. The right way to repair it is by replacing the gasket, but I know it is an expensive job.
Let me know if you have other questions or if I can help.
Tuesday, February 8th, 2022 AT 8:36 PM