I've used old flux before, with no problems. At the end of each use, I make sure to cover the flux jar.
I don't think manufacturers put an expiration date on their flux.
When soldering, it's important not to use too much flux, important to wipe off excess flux and solder when still hot.
For 1/2" pipes and fittings, use 1/2" length of lead free solder.

 

I’ve never had it go bad on me and I have some really old containers of it sitting around.

 

Thanks, all suggestions were/are followed.

 

A bit late to be asking now that the work is done, but does flux go bad or expire?

I doubt it. All my flux is ancient and still works.

 

I still have a round metal can of basic soldering flux I got from a Navy ship back in the '60s and it still works.
it is more of an antique now LOL. maybe I should go clean up the can see if there is a date on it.
brazing flux powder is the same.

 

Same here. I've used really old flux, never any problems.

 

Btw, I was amazed at the >$20 for a roll of solder.

 

Prices went down a bit. I remember paying $25 for a 1 lb roll not too long ago.
But when I do a repipe job, a $5 discount on a roll is irrelevant, when copper (mainly pipes) prices are over the clouds.

 

It doesn't go bad but it can get dirty.
As long as your solder flowed well and you don't have any leaks, then the flux did its job.

 

if I use old solder (which is often) that has the oxidized gray finish, I run it through some steel wool to clean it up.

 

I know it’s an old post, but I have been looking for an article about this subject. I’m having trouble with my 1970’s Kester Paste Flux. It worked fine just a couple years ago, but all of the sudden, the solder is not flowing as it used to. The flux is still the same consistency, but it turned a grayish green color similar to the inside of a plumbing pipe that has been clogged for awhile. It doesn’t smell bad, though. I guess it is time to break down and buy another tin of the stuff.

 

For $3 you would jeopardize a project?? Throw it away and go shopping.