How Much Coolant Does a 2018 Subaru Outback Hold?

A 2018 Subaru Outback typically holds between 7.7 to 8.2 quarts (7.3 to 7.8 liters) of coolant, depending on the engine.

Quick Answer

• Total Cooling System Capacity: 7.7 - 8.2 quarts (7.3 - 7.8 liters)
• OEM Coolant Spec: Subaru Super Coolant (Blue, HOAT - Hybrid Organic Acid Technology). Subaru P/N SOA868V9210 or equivalent.
• Mix Ratio: 50/50 prediluted or mix concentrate with distilled water to a 50/50 ratio.

Capacity by Engine Option

Flush Interval

Subaru recommends an extremely long service life for their Super Coolant due to its high-quality, long-lasting additives.

• Normal Duty: Initial replacement at 137,500 miles or 11 years, then every 75,000 miles or 6 years thereafter.
• Severe Duty: While Subaru does not explicitly define "severe duty" for coolant replacement, if your vehicle is regularly subjected to extreme conditions (e.g., heavy towing, sustained high temperatures, very dusty environments), consider reducing the initial interval to around 100,000 miles or 8 years, and subsequent changes to 50,000 miles or 4 years.

How to Refill & Bleed

Refilling and bleeding the cooling system on a 2018 Subaru Outback is crucial to prevent air pockets, which can lead to overheating.

1. Safety First: Ensure the engine is completely cool before attempting to open the radiator cap.
2. Drain: Open the petcock on the bottom of the radiator to drain the old coolant. For a full flush, you may want to drain the engine block as well, if equipped with a drain plug.
3. Flush (Optional but Recommended): After draining, you can run distilled water through the system until it runs clear to remove any remaining old coolant or contaminants. Ensure all flush water is drained.
4. Refill: Close all drain points. Slowly pour a 50/50 mix of Subaru Super Coolant into the radiator until it's full. Fill the overflow reservoir to the "full" mark.
5. Bleed Air: This is the most critical step for Subarus.
   • Leave the radiator cap off. Start the engine and let it warm up with the heater set to full hot and fan on low.
   • As the engine warms, coolant level in the radiator may drop as trapped air escapes. Continuously top it off with coolant.
   • Look for a bleeder valve or screw, typically on the highest point of the cooling system (often near the thermostat housing or on a crossover pipe). This is crucial for properly venting air. Open it carefully once the engine is warm and coolant is circulating to release trapped air until a steady stream of coolant emerges. Some models may not have an obvious bleeder screw, relying on the radiator opening.
   • Squeeze the upper and lower radiator hoses several times to help dislodge air bubbles.
   • Once the thermostat opens (you'll feel the lower radiator hose get hot), continue to observe the coolant level and add as necessary. You may see a surge of bubbles.
   • Install the radiator cap once steady coolant flow and no more large air bubbles are observed.
6. Test Drive & Recheck: Take the vehicle for a short drive, allowing it to reach operating temperature. After the engine cools completely, recheck the coolant level in the overflow reservoir and top off if needed. Repeat the bleed process if the engine runs hot or if you hear gurgling noises.

Common Cooling System Issues for this Generation (2015-2019 Subaru Outback)

Owners of 2018 Subaru Outbacks, and the broader 5th generation (2015-2019), should be aware of a few common cooling system concerns:

• Head Gasket Leaks (Less Common on Later Models): While historically a Subaru hallmark, head gasket issues, particularly external oil leaks, were less prevalent on the FB25 and EZ36D engines in this generation compared to older models. However, internal coolant leaks (which can lead to overheating or coolant consumption) are still possible, though rarer.
• Water Pump Leaks: The water pump can develop leaks over time, often manifesting as a slow drip or a stain beneath the vehicle. Listen for any whining or grinding noises, which could indicate a failing water pump bearing.
• Radiator Leaks: Radiators can develop leaks, especially around the plastic end tanks where they crimp to the aluminum core. Inspect for pinkish-orange crusty residue (dried coolant) or wet spots.
• Thermostat Failure: A failing thermostat can cause the engine to overheat (if stuck closed) or run too cool (if stuck open). Symptoms include fluctuating temperature gauges or slow engine warm-up.
• Coolant Expansion Tank Leaks/Cracks: The plastic overflow reservoir can sometimes crack, leading to coolant loss. Regularly inspect it for hairline cracks or discoloration.
• Degradation of Subaru Super Coolant: Although it has a long service life, neglecting the coolant change interval can lead to the breakdown of corrosion inhibitors. This can result in corrosion within the cooling system, impacting component longevity.

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