Is Subaru coolant hoat or OAT?
Subaru coolant is HOAT (Hybrid Organic Acid Technology), not OAT (Organic Acid Technology). This distinction matters for maintenance and for selecting the correct coolant when servicing a Subaru engine.
In this article, we explore what HOAT and OAT mean, why Subaru specifies HOAT-based coolant, and how you should approach replacement and maintenance to keep your cooling system protected and running smoothly.
HOAT vs OAT: what the differences mean for Subaru owners
Before you review the list, here is a concise overview of how HOAT and OAT differ in approach and application across vehicles.
- Composition and protection: HOAT combines organic acids with inorganic additives (often including silicates) to provide corrosion protection for metal surfaces inside the cooling system.
- Organic acids only: OAT relies primarily on organic acids without silicates to protect the cooling system, often aiming for a longer service life in some applications.
- Maintenance implications: The two technologies typically come with different manufacturer-recommended replacement intervals and service considerations depending on the vehicle model.
- Compatibility: Using the wrong coolant type in a given engine can lead to corrosion or precipitation; Subaru specifies HOAT-based coolant for its engines to ensure compatibility.
Bottom line: HOAT involves a hybrid approach with silicates and organic acids to protect cooling system metal parts, while OAT relies on organic acids alone. For Subaru, the official guidance is to use a HOAT-based coolant, specifically Subaru-approved products when servicing.
Subaru’s coolant guidance and how to apply it
Subaru’s official materials identify the coolant used in its engines as HOAT-based and recommend using Subaru Genuine Long Life Coolant or other HOAT formulations validated for Subaru vehicles. Following the OEM specification helps ensure proper protection and compatibility with Subaru engines and cooling systems.
To help ensure you’re using the correct product and performing a proper coolant change, consider the following practical steps.
- Verify the coolant type on the product label or in your owner's manual. Look for HOAT or explicit Subaru compatibility on the bottle.
- Use Subaru Genuine Long Life Coolant or a HOAT-based coolant that is explicitly labeled as compatible with Subaru engines. Avoid generic coolants unless they clearly state Subaru compatibility.
- Follow the recommended mixture guidelines. Many HOAT coolants are premixed 50/50 with distilled water, while some concentrates require dilution to that ratio.
- Avoid mixing different coolant technologies. If you must switch from one type to another, a thorough system flush is typically required to prevent compatibility issues.
Adhering to these guidelines helps maintain cooling system protection, prevents corrosion, and preserves heater core and radiator performance in Subaru engines.
Summary
Subaru specifies HOAT-based coolant for its engines, not OAT. When servicing a Subaru, use Subaru Genuine Long Life Coolant or another HOAT-approved product, and follow the label instructions for mixing and replacement intervals. Avoid mixing different coolant technologies, and consult the owner's manual or a Subaru service professional if you’re unsure about the correct product for your model.
