Holley Mid-Mount Thermostat Housing for GM LS & LT Engines

The Holley Mid-Mount Thermostat Housing is a genuine Holley-engineered replacement component designed exclusively for use with Holley's Mid-Mount Accessory Drive Systems on GM LS and LT engines. Purpose-built to integrate directly into Holley's innovative bracketless water pump manifold architecture, this thermostat housing delivers precise coolant flow regulation while maintaining the compact, clean engine bay profile that defines the Mid-Mount platform.

Holley's Mid-Mount system mounts entirely to the water pump housing, eliminating the need for external brackets that bolt to the block or heads. This thermostat housing is engineered to be a seamless part of that system, ensuring correct form, fit, and function without adapters or modifications — delivering a tight, professional installation that keeps accessories inside the width of the exhaust manifolds and solves the clearance challenges common in LS and LT engine swaps.

Key Features:

• Genuine Holley quality — purpose-built as a direct-fit replacement for Holley Mid-Mount Accessory Drive Systems, ensuring correct integration across the entire product line
• Bracketless design compatibility — integrates seamlessly with Holley's proprietary water pump manifold architecture, eliminating traditional external brackets for a clean, streamlined installation
• Flexible heater hose port configuration — multiple coolant port locations, including side and downward-facing options, accommodate a wide range of hose routing needs in swap and custom builds
• Steam tube input port — 1/8" NPT steam port supports proper coolant system venting for reliable temperature management on applicable engine configurations
• O-ring sealed construction — provides a leak-free, long-lasting seal suited to high-performance street and strip applications
• LS and LT compatibility — available in configurations to suit both Gen III/IV LS and Gen V LT Mid-Mount Accessory Drive setups

Holley's Mid-Mount platform was purpose-built for engine swap enthusiasts and performance builders who demand maximum engine bay clearance without sacrificing a fully functional accessory package. Whether used as a replacement on an existing Mid-Mount build or incorporated into a fresh engine assembly, this thermostat housing ensures your cooling system performs exactly as Holley intended — with the reliability and fitment precision that only a genuine Holley component can deliver.