Originally Posted by DaveW

The "jiggle pin" and its hole are also (in add'n to bleeding air) there to assure that some small amount of water flows through the thermostat when it is closed to assure that the wax cylinder (that opens the stat) sees water at engine temperature, and opens when it should.

Originally Posted by ReDLiNe@t9

..... is the ast supposed to be filled with coolant...if so how much....do i manualy fill it or should the car do it automatically?.....

Originally Posted by t-von

I just recently had a lot of mysterious boiling in my engine. I thought the coolant seals were bad. Then I started seeing coolant leaks near the upper radiator hose. Did an inspection and the hoses were fine. I looked over at the coolant reservoir and noticed coolant seeping out of the breather hole on top. I was like WTF. It turned out that my reservoir was over filled and fluid was blocking the breather hole. This didn't allow the AST to properly vent the air bubbles out through the reservoir. I had to siphon the coolant down to the normal level and now everything is fine again. So if you have excessive boiling noises, check the reservoir's coolant level.

Originally Posted by KevinK2

nope. when t-stat is closed, all water exiting block flows across the wax piston exposed on back of t-sat, then flows thru the back port that bypasses the rad and goes to pump inlet.

Jiggle pin is to avoid air pockets, period.