If the cap isn't operating properly, your radiator can't operate properly. Avoid overheating and engine damage. Make sure your radiator has the right cap. These Stant® caps are exact same pressure as factory originals and are available in two types, varying by application. SWIV-EL® Twist-On Caps. OE design makes installation and removal quick and easy. Best for older open-cooling systems and overflow reservoir-type systems. LEV-R-VENT® Caps. Top lever simplifies opening and closing. Great in tight spots where older larger shell caps may not fit