No filter. You might be thinking of the hydraulic fluid reservoir -most commonly CHF 11S fluid reservoir (for power steering rack and active roll stabilization torsional valves controlling the separate halves of the anti-roll bar).
Originally Posted by Mike Swing
What if something bigger like a screw fell in there? Is there filter at the bottom of the reservoir?
The coolant expansion tank acts as a buffer, allowing room in the closed coolant system for the expansion coefficient of the coolant once the engine is turned off.
After the engine is stopped the coolant in the engine and radiator has stopped moving and begins to absorb the heat soak from the engine (big mass of metal that has absorbed heat). As the coolant level rises the expansion tank allows a place for it to flow.
It flows in fairly slowly. After the system begins to cool the vacuum created in the radiator and engine block as the coolant contracts slowly draws the excess coolant from the expansion tank back into the radiator and block.
This is why to accurately check your coolant level you open the expansion tank cap and examine the stick level shown by the float when the system is cold.
Anything large enough to block the action of the float or something like paper or cloth that could be drawn into a different part of the coolant system would warrant disassembling the coolant tank.
If the OP is accurate in his statement that the 3/8" copper tubing is 5" long, there is no chance of it moving from where it is, and IMHO is be best left where it is.
Last edited by bimmerfan52; 09-10-2012 at 08:11 PM.
Reason: Addtl Info