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Im getting an issue with my bike where the back tire is deflating extremely slowly compared to a normal flat where it takes maybe 2 days to be noticeable in terms of lower pressure and maybe a week to fully deflate. Im replacing the tube regardless but wondering if this is the valve broken or just a really small puncture. I did patch a snake bite puncture a couple days ago on the same tire.

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Inflate the tube so it tightens up properly*, submerge it in water and look for air bubbles. That should enable you to locate any holes and/or perhaps a faulty valve. You need some patience, and manipulation(squeezing/bending) of the tube, segment by segment, in some sneaky cases. All while keeping the water pretty calm so you notice the bubbles. Perhaps it was a faulty repair.

You can check the valve at full pressure by putting it in water (using a glass of water with the valve at 12 o clock) while the tire is still on.

*) The tube is not meant to handle full tire pressure without support from a tire. You only need to fill the tube's volume with air and then give it a little extra so it firms up a little bit.

EDIT: added some details I made in the comments.

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    And if this doesn't work, replacing the tube is a valid solution.
    – Criggie
    Feb 24 at 6:24
  • I have had similarly slow punctures (though never for long, they speed up) but in this case I concur with the suggestion of a failed repair. It will probably fail rather rapidly if the tube is pumped up outside the tyre. There is another possibility - a slow leak that caused the snake bite in the first place, but making you ride with too little air in there. Either way the bubbles can be tiny, and need a fair bit of pumping up to find them even in water
    – Chris H
    Feb 24 at 7:26
  • Yes, you want the tube to tighten up properly, I just don't want people to go for 4 bar outside the tire without thinking. You also need some patience, and manipulation of the tube, segment by segment, in some sneaky cases. All while keeping the water pretty calm so you notice the bubbles.
    – WornChain
    Feb 24 at 10:05
  • I've always found my back tire to deflate quicker than the front. I guess there is just some natural leakage that occurs? I always pump it up very firm, but that only lasts for maybe two weeks. Lower pressure stays for months. What time can I expect for a back tire to stay inflated for?
    – YPOC
    Feb 24 at 12:51
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    @ChrisH Exactly. But some people might try to get there because they don't realize the tube itself can't withstand much pressure on its own.
    – WornChain
    Feb 25 at 1:08
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One thing I had quite a few times were loose valve cores. So, it has become a routine to tighten them up with fingers or suitable pliers before I even install the tube.

Symptoms were slow leaks where I had a near flat when parking the bike for about a week while it usually loses just half a bar. Never a problem during rides but annoying on multi-day trips without a proper pump.

From what I heard, this can happen quite often fresh from factory but you probably don't notice because experienced mechanics in bike shops spend the 10 seconds per wheel before handing over a bike.

See How tight does the top part of a presta need to be torqued?

P.S: Your issue seems to be repair-related but I wanted to bring the valve up, just to be sure.

I, personally, would just throw out the tube (and inspect the inner of the tire while doing so) instead of trying diagnose issues on such a cheap part of a bike. Some might call this a waste, but I'd rather spend the time riding the bike. ;-)

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