I'm having a problem keeping my 87 560SEC keeping cool. I did a compression test and it came back even so I don't think it's the head gasket.

I did the coolant flush
Replaced the upper radiator hose
Replace the radiator
Replaced the thermostat
Replaced the radiator cap
Using MB coolant.

Is there a vent screw? I may have air trapped in the system. Any other thoughts?

__________________
With best regards

Al