Is there a UV dye you can use with a DEF system?

I wouldn’t use a dye in the def system. Last thing you need to do is inject it and coat your SCR. Most are oil based, and non of that won’t mix with the catalyst.

Best advise would be to plumb in shop air with it on your jack stands and listen for the leak. If it’s all over then it’ll be audible.

 

Honestly DEF is water and Urea so Kool aid powder should work. Or whatever that Dye that is used by geologists to find water veins.

 

Problem with any sort of dye is DEF is a very specific mix of water and urea. Adding foreign components to it may cause other non leak related issues. And when I say specific I mean that. It's 32.5% Urea to the rest water.

 

Like said above, don’t introduce any other chemicals to the system. It’s a really very delicate chemical reaction taking place. It can just as easily create NOX as remove them. If you get anything on the catalyst (SCR) you’re liable to kill the positive reaction. I’ve done it with city water. I’ve heard of it happening with a little bit ov solvent.

You’ll end up adding another 0 to your cost of repair!!

 

When DEF dries out it leaves a white residue. Like a supersaturated salt solution. If it's leaking, you will see it.