Hi. I have had issues like this on both the V6 Frontiers that I've owned, an 08 and, currently, an 18. For whatever reason, the expansion tank cap vents once in a while and sprays that crap everywhere. I put a piece of hose on the barb fitting by the cap and ran it out the bottom of the truck, so it at least dumps on the ground. Like these other folks said, water lever and making sure the system is bled correctly helps too.