Originally Posted by Snipe656

I was just reading earlier today on a MB forum that with their DEF systems they are supposed to be topped off I think it is every 10k miles and then flushed every 20k miles. The stated reason for the flushing though was to break out or avoid any crystalization issues. Wonder how valid of a reason that is and if it is valid then why they stopped draining and refilling the DEF during oil changes for these cars and now only top off.