If you've never had the heads off, this is worth investigating I think. This guy had a seemingly undiagnosable problem with his BMW i8, a car that cost $150,000 new. Turned out to be a bad head gasket, only way to tell was a CO2 test in the coolant.youtube.com/watch?v=6vOsU2J5MAo
This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=256882