W126 87 560SEC running hot.
 

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?

Fan clutch? The clutch should engage the fan by 90C, which should be noticeable by a whooshing sound.

Thanks for your post. I have heard the auxiliary fan engage but it has a mind of it's own and does not engage at high temps as it should. The fan clutch locks up at high temps and does move a lot of air under it.

What are the symptoms? Does it stay cool (<90C) if you are driving along at say 45 mph? If not, I would check for good water flow. Is the water pump discharge hose harder to squeeze when the engine is running? Also, how is the heater working at the full hot setting? Is the aux water pump working?