Can you put water in a Subaru radiator?

Yes, you can top off a Subaru radiator with water in a pinch, but you should not operate the vehicle long-term with water alone. The safest approach is to use a proper coolant mix (typically 50% coolant and 50% distilled water) as soon as possible.

Subaru cooling systems rely on antifreeze to prevent freezing in cold weather, raise the boiling point, and protect aluminum components from corrosion. Using plain water can lead to overheating in hot conditions, freezing in cold weather, and mineral build-up over time. Always follow your owner's manual for the exact coolant specification and mixing ratios, since Subaru vehicles commonly require a long-life coolant that is compatible with the vehicle’s cooling system.

What coolant your Subaru uses

Most Subarus are designed to use Subaru Genuine Long Life Coolant or an approved equivalent that meets Subaru’s specifications. The typical recommendation is a 50/50 mix of coolant and distilled water, adjusted for the climate you drive in. Do not mix different brands or types of coolant unless the manual specifically allows it.

Dex-Cool and compatibility notes

Orange or amber-colored long-life coolant is commonly used in many vehicles, and Subaru’s specification often resembles or matches these types. Always verify the exact specification for your model year and region in the owner's manual or from Subaru's official guidance—this ensures you’re using a coolant that is compatible with your engine materials and alloy components.

Temporary top-ups with water (emergency guidance)

The following advice applies when you don’t have coolant available and need to get the car to a safe location or a shop. Use water sparingly and prepare to replace with the correct coolant as soon as possible.

• Use distilled water, not tap water, to minimize mineral deposits and scale inside the cooling passages.


• Only add enough water to bring the level to the "full" mark on the reservoir; do not exceed the recommended level.


• Avoid running the engine for extended periods with pure water; it offers no antifreeze protection and reduced corrosion inhibitors.


• As soon as you can obtain coolant, drain or flush as directed by a mechanic and refill with the proper 50/50 mixture.

In short, water topping is a temporary measure. Restore the correct coolant mix as soon as you can to maintain proper protection and cooling performance.

How to properly refill and maintain your cooling system

When you have the correct coolant on hand, follow these steps to refill and maintain the system. Always consult your owner’s manual for model-specific bleed procedures.

• Ensure the engine is completely cool before opening any caps to avoid scalding or pressurized coolant spray.


• Locate the radiator cap (or expansion reservoir cap on newer Subarus) and remove it slowly if instructed by the manual.


• Prepare a 50/50 mixture of Subaru Genuine Long Life Coolant (or an approved equivalent) and distilled water, if using concentrated coolant. If you buy pre-diluted 50/50 coolant, you won’t need to add water.


• Slowly fill the reservoir or radiator to the recommended level, then replace the cap securely.


• Run the engine with the heater on high (to help bleed air from the system) until the thermostat opens and the coolant circulates. Watch for air bubbles and recheck levels, topping up as needed.


• Check for leaks and inspect hoses and the radiator area for moisture or drips. If you notice a leak, have the system inspected by a professional.

After completing these steps, your cooling system should be properly filled with the correct 50/50 mixture, providing optimal freeze protection, boiling resistance, and corrosion protection for Subaru engines.

Safety considerations and signs that something is wrong

Pay attention to warning signals and follow safety precautions when handling the cooling system.

• Do not open the radiator cap when the engine is hot; hot coolant can cause severe burns.


• Check for coolant leaks, puddles under the car, or a sweet-smelling steam coming from the engine bay.


• If the temperature gauge rises toward the red, or you notice overheating, pull over safely and seek professional service.


• Regularly inspect coolant color and clarity. If it looks rusty, sludgy, or has debris, a flush and refill may be required.

Bottom line and practical guidance

Water can be used temporarily to top off a Subaru cooling system in an emergency, but it is not a substitute for the proper coolant. Use distilled water to minimize mineral deposits, and always return to the correct 50/50 coolant/water mix as soon as possible. Adhering to Subaru’s coolant specifications protects the engine, maintains cooling efficiency, and reduces the risk of costly repairs.

Summary

Water is acceptable only as a short-term emergency backup. For ongoing reliability, use Subaru-approved long-life coolant in the recommended 50/50 mix with distilled water, and follow the owner’s manual for fill and bleed procedures. Regular maintenance and prompt attention to leaks or overheating will help keep your Subaru’s cooling system in good shape.

Does Subaru coolant need to be diluted?

You can purchase ready-made mixtures of coolant that already have water additional, or you can purchase full-strength antifreeze which needs to be diluted with distilled water before being additional to the engine system.

Is it okay to put water in a car radiator?

No, you should not put water in your car radiator for regular use, as it lacks protection against freezing and boiling, can cause corrosion, and can lead to overheating and engine damage. While water can be used in a true emergency to get a vehicle to a repair shop, it is only a temporary fix. The correct mixture of coolant/antifreeze and water (often a 50/50 blend) is necessary for proper engine temperature regulation and protection. 
This video explains whether it is safe to add water to your car's radiator: 54sMaxTheCarGuyYouTube · Jan 20, 2025
Risks of using only water

• Overheating: Water boils at a lower temperature (100∘C100 raised to the composed with power cap C100∘𝐶 or 212∘F212 raised to the composed with power cap F212∘𝐹) than a coolant mix, which can cause it to turn into steam and cause dangerous pressure spikes in the cooling system. 
• Freezing: In cold weather, water can freeze and expand, which can crack the engine block or radiator. 
• Corrosion and rust: Tap water contains minerals that will leave deposits and cause corrosion and rust in the cooling system over time. Coolant contains additives that protect against rust. 
• Engine damage: The combination of overheating and corrosion can lead to costly repairs, including a cracked engine block or a damaged radiator. 

When water is acceptable (in an emergency)

• Emergency use only: If your car overheats and you have no other option, you can add water to get to a service station. 
• Use distilled water if possible: If you have to add water in an emergency, use distilled water to minimize mineral deposits. 
• Replace immediately: As soon as you can, you must have the system flushed and refilled with the correct 50/50 coolant/water mix to prevent damage. 

This video demonstrates how to safely add coolant to your car's radiator: 1mCars SimplifiedYouTube · Nov 18, 2023

How to refill Subaru coolant?

To add coolant to a Subaru, first ensure the engine is completely cool and the car is parked on a level surface. Check the coolant level in the overflow reservoir, which is a white plastic tank with "low" and "full" marks. If the level is below the "full" mark, add the correct Subaru-specific coolant to reach the line. If the overflow tank is empty or you've drained the system, you may need to also open the radiator cap (again, only when cool) and fill it to the top before filling the reservoir. 
This video demonstrates how to check and add coolant to a Subaru Forester: 59sSUBARU DRIVESYouTube · Nov 14, 2025
Step 1: Prepare the vehicle 

• Park the Subaru on a level surface. 
• Let the engine cool down completely. Do not open the radiator cap or reservoir while the engine is hot. 

Step 2: Locate the coolant reservoir 

• Find the translucent white plastic coolant reservoir tank, often with "low" and "full" marks on the side. 

You can watch this video to see the location of the coolant reservoir on a Subaru Crosstrek: 35sDIY PintoYouTube · Nov 13, 2017
Step 3: Check and fill the reservoir 

• If the coolant level is below the "full" line, add the correct Subaru coolant (or an equivalent) to the "full" mark. 
• Replace the cap securely after adding coolant. 

Step 4: Check the radiator (if necessary)

• If the reservoir is empty, you may need to fill the radiator itself as well. 
• Caution: Only open the radiator cap on a cool engine. Press down on the cap and turn it to the left to release it. 
• Fill the radiator with the correct coolant until it is near the top. 
• Replace the radiator cap and tighten it securely. 

Important safety and general tips

• Use the right coolant: Always use the specific coolant recommended for your Subaru model to avoid damage. 
• Avoid mixing: Never mix different types of coolant, as this can cause problems. 
• Be careful with spills: Coolant is toxic, so wipe up any spills and dispose of coolant properly. 
• Look for leaks: If you need to add coolant frequently, it could indicate a leak. It's best to have your Subaru checked by a professional. 
• Dashboard light: If the low coolant warning light comes on, have your car inspected soon to prevent engine damage. 

Can you put water in a coolant tank on a Subaru?

If you do not have proper radiator coolant with you, then you can top up your radiator with water in an emergency — but only in an emergency. Water is not a good substitute for coolant because of its long-term effects on your vehicle's health.