Coolant overflow tank levels

[parraeel]

Not sure if this is serious yet, I've noticed that the levels in the Coolant overflow tank have been dropping slowly over about the past 5 or so weeks. I topped it up to just under the "MAX" line, and in those 5 weeks, it is just below the "MIN" line. The car hasn't overheated and is running good, and there are no drops of water under the car.

I have also found the overflow tank cap extremely hard to unscrew,to the point of needing to use pliers to get it moving, even when the car hasn't been running. It feels as though the thread on the cap might not be as good as it should be. Could a bad cap cause any coolant loss from the tank?

Thanks all.

[jets]

I can't offer any help on where the coolant is going apart from maybe one of the combustion chambers through the head gasket.
As far as the tight cap, I have applied a smear of vasolene on the threads that works on mine.
Pop the bonnet open when hot while under pressure & check for any leaks around the cap & elsewhere around the engine.

[kaanage]

If the thread has been cross-threaded, then the system may not be fully sealed anymore so the coolant could evaporate slowly. Is there pressure in the system when you undo the cap straight after switching off?

[pontiff]

If the thread has been cross-threaded, then the system may not be fully sealed anymore so the coolant could evaporate slowly. Is there pressure in the system when you undo the cap straight after switching off?

im not sure if places like supercheap auto have them but you could pressure test the cooling system and see if there are any leaks... what does the oil look like? not milky in any way? thats not a small amount of water to be losing so it has to be going somewhere.... No leaks on the ground?

[parraeel]

Had the cooling system pressure tested, the tester was on all day, no change in pressure. Also changed the oil and it looked normal, not milky at all. So at this stage I will put it down to a faulty coolant tank cap.