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).Designed as a direct replacement for the OEM unit, this thermostat housing mounts in the factory position with the radiator outlet maintaining the upward angle.The housing features a threaded water outlet port that accepts a 1.25-inch radiator hose fitting or 12AN/16AN fittings.The outlet uses a 16OR (1-5/13-12 SAE) thread with an seal to leak-free performance.Two additional ports are included—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 in use.An M6 threaded hole is machined into the housing for the engine harness ground ring.Installation is straightforward, requiring only two bolts and located adjacent to the intake manifold.Dual hole configurations allow compatibility across the specified model range.Some transmission setups may require minor adjustments.Not compatible with certain scattershields.