Thermostat Housings, Filler Necks, Restrictors & Water Outlet Housings

What a Thermostat Housing Does in Your Cooling System

A thermostat housing holds the thermostat in place and gives coolant a sealed path from the engine to the upper radiator hose. Most housings bolt to the intake manifold or cylinder head, with the thermostat seated underneath. When the engine warms up, the thermostat opens and coolant flows through the housing toward the radiator.

You'll see the same part called a water outlet housing, water outlet or water neck, depending on the manufacturer. Some shoppers search for it as a radiator housing, though that term isn't standard. Whatever the name, the job stays the same: seal the thermostat, aim the hose and handle heat cycles without leaking.

Because the housing ties into the rest of the system, it pays to check related parts while you're working. Browse cooling, heating and A/C parts for the full system. If you need a new thermostat to go with your housing, visit thermostats, housings and hoses.

Types of Thermostat Housings and Water Necks

Thermostat housings come in a few basic styles, and the right one depends on where your upper radiator hose needs to go. A straight-up housing points the outlet vertically, while angled and swivel designs let you aim the hose around brackets, accessories or a tight radiator inlet. Here's how the main styles break down:

• Straight-up housings, like the Speedmaster polished aluminum water neck for SBC 350, suit stock-style hose routing
• Angled housings, such as 45-degree and 75-degree swivel water necks, turn the outlet toward the radiator
• 360-degree swivel housings, including Meziere designs for SBC, BBC and big-block Chrysler, rotate to any position
• Inline housings mount in the upper hose instead of on the engine
• Spacers and risers, such as a 1-inch-tall billet water neck spacer, raise the outlet for added clearance

Swivel styles help on custom builds where hose routing changes after you swap a radiator, water pump or intake manifold.

Aluminum Thermostat Housing vs. Plastic and Steel Options

An aluminum thermostat housing is the common choice for performance builds. It's light, sheds heat well and can be polished to match your engine bay. Most aftermarket housings are cast aluminum, which handles everyday street use.

Billet aluminum parts are machined from solid stock for a crisp look, while stamped aluminum keeps weight down. You'll see all three materials in filler necks too. Moroso offers a cast aluminum filler neck kit along with billet and stamped aluminum filler necks for SBC and BBC engines.

Many late-model vehicles use OE-style integrated housings that combine the outlet and thermostat in one assembly, often in plastic. This category includes an integrated assembly for the 2011-2015 Chevrolet Volt.

Some aluminum outlets also build the housing in, like the Weiand water outlet that includes its own thermostat housing. Steel water necks, such as the one for big-block Ford 429-460 engines, suit owners who want a factory-style part.

Radiator Filler Necks, Restrictors and Sealing Parts

A radiator filler neck adds a fill point to your cooling system, which helps when the radiator cap sits low or out of reach. An inline filler neck for 1.25-inch hose splices into the upper hose. A radiator cap filler neck kit or a filler neck expansion tank for SBC/BBC gives you other ways to mount the cap.

A thermostat housing restrictor controls how fast coolant flows out of the engine. It's common on race engines that run without a thermostat, since it gives coolant time to shed heat in the radiator. Pair these parts with the right radiators and radiator components to complete the system.

Sealing parts keep everything leak-free. You'll find thermostat housing O-rings, thermostat gaskets and thermostat housing bolts, including bolt sets for 1966-1972 SBC/BBC engines. If you're chasing a seep, read our guide on how to find and fix coolant leaks.

How to Choose the Right Thermostat Housing for Your Engine

Start with your engine family, since the bolt pattern and mounting surface vary between engines. This category covers SBC 350, big-block Chevy, big-block Chrysler, 1965-1975 Ford 289/302/351W and big-block Ford 429-460 applications. Use the vehicle selector to filter for parts that fit your year, make and model, then narrow by outlet size and style.

Next, check these fitment details before you order:

• Hose diameter, so the outlet matches your radiator and heater hoses
• Outlet angle, so the hose reaches the radiator inlet without kinking
• Clearance around the alternator, brackets, distributor and hood

Swapping radiators can move the inlet, so confirm hose routing before you buy a housing. Our guide to installing an aluminum radiator in a classic car walks through fitment. If your engine uses a bypass circuit, you may also need new coolant bypass hoses.