How to Check and Refill Coolant Levels: A Step-by-Step Guide

Whether you're taking care of your personal vehicle or keeping a fleet running smoothly, checking and refilling coolant is a quick and essential task.

What to Expect

• Time Needed: 5-10 minutes
• Difficulty: Easy
• Average Cost: $6

Source: 2025 Fleet Benchmark Report

What You’ll Need

    Coolant (check owner’s manual for the correct type)
    Funnel
    Gloves & shop rags
    Distilled water (if coolant needs to be mixed)

How to Check and Refill Coolant Levels

Step 1: Let the Engine Cool Down

• Park on a level surface and turn off the engine.
• Wait at least 30 minutes before opening the hood to avoid burns from hot coolant.

Step 2: Locate the Coolant Reservoir

• Open the hood and look for a translucent plastic tank near the radiator.
• The tank should have MIN and MAX lines to indicate fluid levels.

Step 3: Check the Coolant Level

• If the coolant is between MIN and MAX, levels are fine.
• If the level is below MIN, it needs a refill.

Step 4: Refill the Coolant (If Needed)

• Remove the reservoir cap slowly to release any pressure.
• Use a funnel to add coolant until it reaches the MAX line.
• If using concentrated coolant, mix it 50/50 with distilled water unless otherwise specified.

Step 5: Secure the Cap & Inspect for Leaks

• Tighten the coolant reservoir cap securely.
• Check under the car for leaks or puddles that could indicate a bigger issue.

Avoid These Common Mistakes

• Opening the cap while the engine is hot. Hot coolant can spray out under pressure, causing serious burns. Always wait for the engine to cool down before checking or refilling.
• Using the wrong type of coolant. Different vehicles require different coolant formulas. Mixing incompatible coolants can cause sludge buildup and reduce cooling efficiency.
• Overfilling the reservoir. Filling past the MAX line can lead to overflow and system pressure issues. Always keep the level within the recommended range.

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FAQs

How often should I check my coolant levels?

Coolant levels should be checked at least once a month and before long trips. Fleet vehicles or those in extreme climates may need more frequent checks.

Can I use water instead of coolant?

Only in an emergency. Water alone doesn’t provide the anti-corrosion or temperature-regulating properties of coolant. Always use a 50/50 mix of coolant and distilled water unless your vehicle requires premixed coolant.

How do I know if my coolant needs to be replaced?

If the coolant looks dirty, rusty, or sludgy, it should be flushed and replaced. Most vehicles require a coolant flush every 30,000 to 50,000 miles.

How much does coolant cost?

A gallon of coolant typically costs $10 to $30, depending on the type. A full coolant flush at a shop can range from $100 to $200, including labor.