Radiator cap leaking air?

[JoeDellio]

When I squeeze my upper radiator hose (with car on or off) I can hear air escaping out of it. Im guessing this isnt normal? Ive been having a hard time bleeding my system and I wonder if its because it wont pressurize correctly.

[Meatball546]

Are you sure it's actually air coming out of the cap, and not just coolant moving into the reservoir? To bleed it, the system can't be pressurized. You need to be adding coolant to bleed it...

[JoeySully]

this happened to me on my 318 when just after i changed my thermostat.
there is a little valve inside the cap that get stuck open i believe.
i swapped it for another one. check that you don't have a crack at the neck though. Also bleeding the system is not easy even on a 318 and could have been the cause of this.
What i did was take a 2l milk bottle and cut the bottom off it. it fits nicely into the radiator filler spout then using electrical tape I taped the milk bottle to the rad filler spout. then filled the milk bottle up to the top and with the bleed screw out kept filling until coolant came out the bleed screw. I then tightened the bleed screw and filled the milk bottle again. i squeezed the pipes repeatedly topping up the bottle when necessary. i was surprised by the amount of air that came out.
even after all this i took it for a drive and could hear bubbles going through the heater matrix so got back home and repeated the procedure above and got more air out. hope it helps

[JoeDellio]

I have a brand new radiator and resevoir. When the car is off I can squeeze the upper hose and hear air coming out of the bottom of the cap. Its probably the original cap. I think I might replace the o-rings for the hell of it first.

[espguitarist]

Also check the bleed screw itself. Mine somehow managed to get sheared off and was leaking.

[JoeDellio]

Bleed screw is fine, its a brand new radiator. My thermostat housing is leaking, so Im guessing I cant get all the air out of it when I bleed it and then when it gets pressurized it leaks out. Im gonna check it out once I swap in a new gasket (Im doing the FDM next week)