I just go through the "engine" and "cooling" sections of ECS website and fill my cart up with the appropriate parts (and making sure on RealOEM the parts are correct):

When I bought my tensioners, belts, etc from ECS it wasn't many parts, I purchased a hydraulic tensioner unit for the main belt, an ac belt tensioner, new idler pulley and hardware, and the 2 belts.

If you go on ECS "cooling" section they sell a "level 1" cooling replacement kit for 400 bucks, which includes a new T-stat, aux fan switch, upper and lower rad hoses, water pump, and a gallon of coolant. Make sure you get the kit that is "OEM Genuine parts" only, our cars are very sensitive with cooling system as is, and as X5SND will chime in, he originally had a GEBA water pump replacement which he is now switching out because of sub-par performance compared to stock. Get the OEM water pump and the OEM cooling kit.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards