Engine Coolant Replacement Reservoir Cap (31406) by Gates®. Pressure: 16 psi. Type: Closed System. Shell Diameter: 3.3″. Filler Neck Outside Diameter: 1.23″. Cap Depth: 1.3″. If you want to keep your vehicle safe on the road for many years to come, go with this Gates product. Developed with the utmost attention to detail and manufactured from the highest quality materials, it is sure to provide a long-lasting service life.