That plastic container or reservoir is called the 'de-gas' bottle. It is where bubbles embedded in the coolant can float to the top into the volume above the coolant level. The bottle is under pressure when the system is hot and the cap tightened, so do NOT open the cap without taking precautions when it is HOT.
I think there is a maze of plumbing on the forward side of the engine. With the engine stopped but hot, you may be able to sniff around under hood and determine where the odor is the strongest. If you have not done it yet, I would suggest dropping the 'pan' covering the bottom of the engine & transmission. Take a good close look for damp areas and coolant 'trails' as I think you may have a coolant(water) pump leak. If you have the right years/miles it may be covered by the original warranty. A brother had an E that had coolant odor that one daughter drove. He's big, so maneuvering to find the source of the odor was not easy but it turned out to be hoses/pump(definite maybe) above the aero/drip tray on the front side. The repair was covered by warranty, saving a bit of hassle.
If it is an ecoboost, you may want to find out if it eats coolant. If it does, it may have a leaking head gasket. The solution or fix for that leak is a new short block or a used engine. The problem may have been solved by the 2018 model year.
If you are not under warranty, see if you can purchase a basic engine and transmission extended warranty. You may get a reasonable quote from YAA - Your Auto Advocate, yaa.com as they offer them at pretty low markup. Either way you can bargain for the cost of the warranty. They are retail items sold by dealers, and others, and you may even find on DaRiver or DaBay. You can choose the time/miles/coverage you want above and beyond the Emissions and Powertrain warranties. The prices will reflect that you want base engine to bumper-to-bumper for low annual miles or for "We drive 20,000 miles a year" coverage. Ask YAA for an estimate and they will send a table of choices to tailor to your expected use.