2011 dd15 black overflow tank

[race7820000]

I know this us a old thread but wasent losing coolant after I took out filter and changing clamps but the tank got darker and darker.

It ended up being the hose from egr cooler to tank. I put a 3/8 hose on there when I changed the cooler a year ago and it was for fuel and the antifreeze ate the inside. It was so bad when I took hose off it was hard as a rock and when i cut it open to look inside hose you could see the webbing of the hose itself. I got a new tank and she has been clean ever since. I used silicone hose this time though

So definitely check hoses lol its always something so simple.