When does DEF fluid go bad.

[ernie1]

Due to unforeseen circumstances, I've had DEF fluid in my rv system for about a year now because the rv hasn't been driven and may sit for a few more months. When do I start to worry and have to drain it out. If I do have to drain it, how do you do on a 2017 Mercedes Sprinter 3500?

[ernie1]

NRAlifr; Thanks for the explanation

[NRALIFR]

I wouldn’t worry about it.

DEF doesn’t “go bad”, it gradually looses it potency over time. The best way to test its potency is to use a DEF refractometer that’s available for about $25 on Amazon. But, using old DEF that’s less than 32.5% pharmaceutical grade urea will not hurt your engine or exhaust system. It will simply use more DEF than it would normally.

:):)

[ernie1]

Thanks guys for the good info. Think I'll take and use info from everyone. I'll wait a bit and not worry about the age of the DEF but if I find that I'm gonna be homebound for an extended period of time I'll siphon it all out.

[chindog]

When we got stuck for an extended period of time due to the plague, I drained our DEF tank using a siphon hose, and replaced the fluid with fresh juice before we started out. We were in central Florida, so there were lots of hot days, and that is a killer for DEF longevity.

[MDKMDK]

I would suggest 2 options, based on 3 years of experience.

1) ask your local MB Sprinter dealer your question, and get the official MB answer.

2) Don't worry about it. I'm in the same "no travel" situation (I do take it out and exercise it, weather permitting, on shorter trips), and have had the current DEF supply in my tank for well over a year. Now I live in Canada, so it's been "stored" at lower temperatures for much of that time, so that might help. Anyway, if there's a problem with it, the MB ECU will tell you with a CEL, and then it might be time to do something about it, like get it into a MB "qualified workshop" as the manual calls them, to get it checked. Let them drain it if that's the actual issue. Other than that, as I said, don't worry about it, until some CEL pops up that tells you to worry about it.

[Rick_Jay]

Hi,

I'm not an expert by any measure on diesels, but I found this link on Commonly Asked Questions About DEF.

Wow...I just learned a ton of stuff about DEF! LOL

This is probably most relevant to your situation from that link: "If stored between 10 and 90 deg F, shelf life will easily be one year. If the maximum temperature does not exceed approximately 75 deg F for an extended period of time, the shelf life will be two years."

No "easy" answer, as it depends upon the temperature, but it looks like you could be nearing the expiration point if you have many days above 90 degrees F.

I hope this helps.

~Rick