86 Golf Diesel cooling ball with hole???

[SR Heer]

Here while back I was trying to figure out why my 1.6L diesel 86 Golf was overheating a bit - it never would peg meter but definitely register in the upper 3/4s to 7/8s of gauge indication.
Found out part of problem to be a pin hole in coolant hose.
In the meantime while looking at coolant system I noticed a white plastic ball in small hose going from radiator and close to expansion tank .
I removed it figuring it was restricting flow and have since misplaced it - now I realize it might be important to have slight back-pressure or some flow restriction on coolant entering tank - so my question is does having a flow restriction help heat transfer in radiator and how important is this ball? What are they called? - If I cannot order I was thinking of getting a wooden dowel that would just fit inside return tube and drill proper size hole in middle - What size hole should I drill?
Thanks for any comments and or information!     

[vanbcguy]

It will be fine without the restrictor. They often get plugged up as they get old anyhow, causing folks to remove them.

The ball is there to get air out of the system. It is the high point. The flow through the small hose gives a pathway for air bubbles to reach the ball while the lower hose on the ball returns air-free coolant to the system.

[fatmobile]

Sometimes coolant can flow into the resevoir so fast that it splashes against the side,.. near the cap where the pressure relief valve is.
 The little extra bursts of pressure, in addition to normal operating pressure, can cause the valve to pop open and leak coolant.

 Not sure if this is the case on the round resevoir seems like it has a divider to block it from splashing on the cap.
I have seen it on the earlier MK2 resevoirs that in the MK1s have the often clogged restrictor in the radiator outlet barb.