Flat tire. Do I need to replace the tube?

Question

My back tire got flat. If I pump it up now, it can hold the air for about 30 minutes to an hour before it's totally flat.

I took out the inner-tube yesterday, pump in a bit air and put it into water, trying to find a hole but couldn't find anything.

Could it be that the tire is too old and I must replace it?

EDIT: thanks to all your response. Beside soap water, I found out hot water is really helpful and that was what I used to fix my tire. There was a very tiny hole on the tube that I couldn't find when I used room temperature water.

Answer 1

Sometimes it can be hard to find a small hole. Sometimes it helps to mix water and dish soap together and either pour that over the partially inflated tire, scanning for leaks or submerging the tire in a bucket of soapy water. The soap will bubble and make holes more apparent. You also probably want to immerse the valve to see if the leak may be originating from there.

If the problem is coming from the valve, then you will want to go ahead and just replace the tube.

Answer 2

To answer the question directly, yes, if your tube is losing air that quickly, it needs repair. It is not a matter of simply being too old.

There is likely a very small hole or a leak in the valve.

Replace the tube, or patch it. Benzo's soapy water suggestion will work very well.

Answer 3

Take the tube out and pump it up so that it balloons to 2-3 times its normal size. There have been times when the puncture is too small to detect in normal situations, even soapy water, but this has never failed me! Even the smallest puncture, like from a brake cable sliver, will show itself. Listen for the hiss and then mark it with a pen to find it after you deflate it (Usually I make 4 lines coming out away from the hole, like an X but with the middle taken out, this pic is just an X, but the 4 lines makes it easier to pinpoint).

If this doesn't produce any results it might be in the valve. If you have a Schrader, get your finger wet and put it lightly over the top (I spit on the ground and put my finger in it) this will allow you to feel any air leaking out. With a Presta it is a little harder, but wrap your wet thumb and index finder around the top of the valve to check it. Most of the time you can fix the Schrader using a core tool, not sure you can do anything to fix a Presta (but aside from a bent core bolt I've never seen a Presta valve leak)