AST cap hissing and rad cap gurgling???

[wiggman2030]

Yeah i know it\'s another coolant leak thread and believe me i have looked though most of them but couldn\'t find anything on AST caps hissing....
Basically my rex is losing water and i know it has a dodgy seal but it shouldn\'t be losing this much water (hopefully).  I have to put in about 300ml everytime i take her out only to find that all of it gets dumped on the road after turning it off for a while. The weird thing that i don\'t understand is why it never replaces lost water from the expansion bottle on the drivers side... When i fill the car up i check the rad to see how much water it has lost which is usually quite a bit, then replace the cap and fill the AST which is usually empty too.  I\'m not sure if this is normal or not but when i fill the AST it fills normally but no water is being passed to the rad until i remove the rad cap, then all of a sudden water fills it to the correct level from the AST. Im thinking dodgy cap maybe :S also once the car has been out for a drive i can hear a small hissing noise from the AST cap and a gurgling noise from the rad cap, is this normal?

The car still starts ok unless it\'s been left for 3 days, then it\'s a bit grouchy but still it starts.. could anyone shine any light on this?

Thanks

[NurburgRob]

I get hissing and a mega gurgle about miute after turning it off.  Mine also looses about 250-300ml after each journey.  Runs fine, starts fine and still goes like stink.

I had a hydrocarbon test done at WGT and its the water seal, it\'ll blow big time at anytime!!

Sorry pal, I\'d get it to a tuner to do a hydrocarbon test.

[Aubec]

Think you can get hydrocarbon test kits in halfords and the like?

You\'ve probably got a pinhole leak between the AST and the expansion tank- hot water under pressure will flow to the expansion tank, but on cooling it\'s just sucking air through the leak rather than water back from the expansion tank.

I have the same problem, just saving up for a new radiator then I\'ll do all the hoses at once.

[Aubec]

Oh, and fill at the radiator cap, not the AST.

[wiggman2030]

Thanks for the help people, i know it\'s the water seal that is the problem but it just bugs me as to why water i lose never gets replaced even though it has it in the system... There probably is a leak somewhere between the AST and the expansion bottle but why would this stop water going from the AST into the radiator until i take the radiator cap off??? It doesn\'t make sense cause if it was a leak causing the problem taking the rad cap off is just creating a massive hole which somehow lets water through...if it had to be air tight the water should be more likely to pass through with the cap on rather than taking it off.  Thanks anyway guys just have to save for a rebuild (ouch).