deflating tyre mystery?

I've definately had goblins before, a tube that's been completely fine - come out one morning to it being entirely flat.   Pump it up again and it's all good, back to requiring a top-up once a week.

I reckon it's various spouses having fun with us.

Has the tube been patched already? A patch can leak under normal pressure even though it holds air at low pressure when pumped up out of the tyre.

It could also be a very small hole. If water can't find it when the tube is pumped up really fat then bin the tube.

Solution: re-install the tube, inflate to high pressure, turn the wheel around in a bucket of water and you'll find the leak.

Two months ago I had the exact same problem. Tube out, inflate, put it into water to find the hole. No bubbles what so ever. Valve was also ok. Even with a flash light I coulnd't locate any holes.

Then it hit me - you can only inflate the tube so much before it explodes. Therefore, in order to inflate it to, say 100 PSI, you need the tyre on. That's what I did. Next, fixed bike to repair stand, tilted back wheel downwards so it could immerse in the bucket of water.

In two seconds I found 3 places where tiny bubbles slowly were coming out of the tube. As there were 3 holes rather close to each other I installed a new tube and new tires front and back as they were rubbish anyway.

Good luck.

Couple of tricks. Over inflate the tube (go as big as you like, it will expand to as big as your forearm  without causing damage (and it will bulge)). Then put it in a bucket of warm water with a little dish drops in it (surfactant you see, and makes the bubbles more obvious) Put the valve under as well. You will almost certainly find if / where it's leaking. The problem does sound like an intermittent valve leak, so as others have suggested take the valve out, wash it (to get rid of any grit which may be responsible for letting air through) and then screw it firmly back in to the valve stem.

If none of this works it's definitely goblins, and there's no cure for them.

"I took the tube out, put some air in and couldn't find any holes."

I overflate inflate the tube to an inch (25mm) in diameter then immerse it in a bucket and/or sink full of water.  Overinflation causes bubbles from the tinest of leaks - valve core, seam, pin prick etc.

Check the valve core. I bought some of little tools to tighten them up for not much more than £1 and they work a treat rather than using grips!

Sometimes there really isn't a hole in the tube nor a disfunctional valve.  It is the goblins who live in the garage next to my bike who sneak out and deflate the tyre in order to annoy me.

Another possible reason for the 'ok-ok-flat' syndrome is when the inner is at the correct pressure it is pressing on the tyre so there is a slow rate of air loss however at an impossible-to-predict point in time, that pressure will not be sufficient and it deflates comparatively quickly

I've used all the methods above for finding punctures and would add the back of hand or even lips as they are more sensitive than your fingers

Had this a while back - eventually figured out the valve core was being unscrewed slightly every time I pumped it up and tightening it up by hand wasn't enough. A good twist with some mole grips sorted it. 

Take the tube out, pump it up and then submerge it in water to see where the bubbles are coming from. 

Possibly the valve. Also how old are your tubes and how thin are they? 

it could be them that's the problem. Rubber and latex are porous and will leak air over time. I've personally found that certain brands deflate quicker than others. 

As you said, almost certainly the valve.

I've had this on a couple occasions - could also be a really small puncture, especially along the lines where the tubes are joined together.