I'd pull that tank and clean the gunk out. See my post at
viewtopic.php?f=5&t=66774&p=735880&hilit=+coolant#p735880 for hose routing. To remove the tank on cold engine, remove cap, open radiator drain on lower left of radiator (2cm off a 10mm allen wrench fits inside the drain fitting and makes undoing it easy) and drain enough to empty tank; undo the 2 firewall bolts; slide the tank slightly forward off the metal base (when putting back on the tank can just sit on top of this base); remove the low coolant sensor wire on the bottom; remove hoses during this process as convenient; clean tank and reinstall.
Looks to me like someone did not use HOAT (Mopar, Xerex G-05, Ford equivalent) antifreeze or if they did it's way out of date so I'd completely drain/flush the system. NOTE just draining will not remove all the old antifeeze, you either need to have the system flushed or do multiple drains and refillls to get ALL the old antifreeze out. See my posts (including the embedded link) at
viewtopic.php?f=5&t=64339&p=711030&hilit=zerex#p711030 on how to do this. A 50/50 antifreeze/water mix requires about 1.6 gallons of HOAT (add undiluted to system then complete fill with water, it will mix as you drive)
2 added thoughts:
1. demineralized water is good to use and cheap by the gallon at any grocery store
2. probably would be a good idea to pull both heater hoses and GENTLY use a hose to flush the heater core to remove any gelled coolant from it. FYI our heater system has no valve in the coolant lines so there is not real need to set the heat to hot.