wmburns
SN Certified Technician
Another possible source of air in the cooling jacket could be the intake. I am not familiar with the OP's supercharger set up. But if the intake gasket is leaking at the cross over, this could allow boosted air into the cooling jacket.
IMO, this is a long shot as most likely it would work both ways and pull coolant into the intake at idle. Likely resulting in white smoke out the exhaust.
Looking at the pictures, the anti-freeze concentration looks high. At high concentrations, anti-freeze does not carry heat as well. While the boiling point is higher, it is carrying much less heat than it should. This can lead to slow overheating.
It would help to know how the coolant temperature before/during/after this problem happens.
IMO, this is a long shot as most likely it would work both ways and pull coolant into the intake at idle. Likely resulting in white smoke out the exhaust.
Looking at the pictures, the anti-freeze concentration looks high. At high concentrations, anti-freeze does not carry heat as well. While the boiling point is higher, it is carrying much less heat than it should. This can lead to slow overheating.
It would help to know how the coolant temperature before/during/after this problem happens.