My final thought.
If you don't over fill these enignes, they will never purge the air out of the coolant system. Since air is easier to pump than water, there will be a bubble in there until filled to the max. The top most hose on the coolant reservoir is the purge. It looks like woven hose usually and if you follow it, it will go towards the r/f fender where it exits.

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Benzmac:
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
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