Thermostat housing with 1.25-inch connector for B and D series engines Applications: All 1988–2001 B-Series engines and all 1988–2000 D-Series engines (excluding D16Z6).This thermostat housing provides additional cooling system configuration options.The billet aluminum housing is machined to replace the unit and mounts in the factory location, with the radiator outlet maintaining the upward angle.The main feature is the threaded water outlet port on the housing body, compatible with a 1.25-inch radiator hose fitting or 12AN/16AN fittings.This design eliminates the need to weld bungs onto older cast aluminum housings.The radiator hose fitting uses a 16OR thread (1-5/13-12 SAE) and seals with an to prevent leaks.The housing includes two extra ports: one for a fan switch and one 1/8 NPT port for accessories such as gauges.A plug is provided for the 1/8 NPT port if not used.An M6 threaded hole is included for the ground ring on the engine harness.Installation is straightforward, as the housing mounts next to the intake manifold using two bolts.Dual hole positions allow fitment across all applicable B and D series engines.Slight modification may be necessary depending on transmission type.Clearance may be limited with certain scattershields.