I too bleed air from this screw that Greg speaks of whenever I flush my coolant system.

I believe your '90 103 engine has it. I do know that older MY 103's had the thermo-valve in this spot but was subsequently moved to the fender wall.

Good luck

__________________
-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi