IS A 156° THERMOSTAT RIGHT FOR YOUR SUBARU? WHAT YOU NEED TO KNOW
Performance thermostats like the IAG 156° Low Temperature Thermostat offer real benefits for heavily modified or track-driven EJ engines—but they’re not always the right fit for every setup, especially daily-driven street cars. We’ve seen a few customer reviews raising valid questions about how this upgrade affects engine warm-up, fuel economy, and overall performance. If you're wondering whether a low-temp thermostat is right for your build, this article will help break it down.
WHAT DOES A LOW-TEMP THERMOSTAT ACTUALLY DO?
The thermostat in your Subaru’s cooling system controls when coolant begins circulating through the radiator, directly impacting how quickly and efficiently the engine regulates temperature. The factory thermostat doesn’t begin to open until around 172°F (78°C), which helps the engine warm up quickly—but can also delay cooling under heavy load. In contrast, the IAG 156° Low Temperature Thermostat starts opening at 156°F (69°C), allowing coolant to circulate sooner. This earlier activation helps reduce the chance of sudden temperature spikes and improves overall cooling efficiency, especially during aggressive driving or track use.
WHY LOW TEMPS MATTER IN PERFORMANCE BUILDS
In a tuned or track-driven Subaru, high cylinder pressures, aggressive timing, and elevated turbo temps can push your cooling system to its limits. A lower-temp thermostat helps combat this by allowing earlier coolant circulation, keeping temperatures more stable and reducing the risk of heat soak or detonation. This is particularly important during repeated hard pulls or lap sessions where managing heat is a constant battle.
BUT WHAT ABOUT STREET CARS?
This is where context matters. On a street-driven WRX or STI, especially one that sees shorter trips or colder ambient temperatures, a 156° thermostat may prevent the engine from reaching full operating temp. This can lead to:
If you're not seeing consistent hard driving or engine temps above normal, a factory-range thermostat might be the better option for longevity and drivability.
IS YOUR SUBARU THE RIGHT FIT FOR A 156 DEGREE THERMOSTAT?
The IAG 156° Thermostat is best suited for:
It's not recommended for:
BUILT TO PERFORM — AND LAST
If you're pushing your Subaru to the limit, you need components that can keep up. IAG’s 156° Thermostat is designed with longevity in mind. Constructed from 304 stainless steel to resist corrosion and endure high temperatures, it includes a quality gasket for a reliable seal. The laser-etched IAG logo reflects the precision and craftsmanship behind every part we make.
PERFORMANCE vs. PRACTICALITY
The IAG 156° Low Temperature Thermostat is a proven upgrade for drivers who push their EJ engines hard and need faster coolant circulation to manage temps. But like any performance part, it’s important to match it to your goals. If you're building a high-horsepower street machine or prepping your WRX or STI for track use, this thermostat is a smart investment.
Have questions about your setup? Feel free to give us a call at 1(410)840-3555 or send us an email at sales@iagperformance.com—we’re happy to help you choose the right components for your build.