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Cap is securely screwed on, no slop. New tank. Drips coolant from under the cap. Used to be a pretty good stream, now it's a dribble but still leaks. Any idea? Should I try swapping out the car now? Also what connects to the smaller input at the top? Mine was plugged before so I just plugged it.
Leaks where? Any coolant that makes it past the pressure cap should be free to enter the hose in your picture and exit there. Really this should never happen unless being overheated or over pressurized. Head gasket failure, etc.
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
The small hose is the overflow. If you capped it, the pressure maybe building too much. Do not cap it and your cap leak will probably go away. Also you may have filled the reservoir with too much coolant so when the engine heats up and the coolant expands that water has to go somewhere. Normally it will go to the expansion tank between the fender and fender plastic. And when there is negative pressure (when the system cools down) the system will refill from that overflow tank back into the reservoir.
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Also what connects to the smaller input at the top? Mine was plugged before so I just plugged it. 
