Fit For: 2006-2007 Volvo VNL Base Straight Truck - Long Conventional l6 2006-2007 Volvo VNL Base Tractor Truck - Long Conventional l6 What is a Coolant Tank: It is typically connected by a tube to the radiator filler neck, and can serve as a place for excess coolant to be captured when the pressure release valve in the radiator cap gives way. In a properly operating cooling system, the coolant will then be siphoned back into the radiator as the temperature drops. Features: .