How to Check and Add Radiator Fluid

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Your car's radiator is the heart of its cooling system, which also includes a fan, water pump, thermostat, hoses, belts and sensors. It directs coolant around cylinder heads and valves to absorb their heat and return it to the radiator and dissipate it safely. Because of this, you need to maintain an adequate radiator fluid level at all times, which means you need to check the coolant level and add to it when necessary. Here's how.

Steps

Checking the Radiator Fluid Level

1. 1
   Park the car on a level surface. Ideally, you should do so after driving the car a short distance. You want to check the antifreeze/coolant level while the engine is cool or lukewarm, not hot or cold. If you have driven the car a longer distance, let the engine cool for several hours.

   
   

   • Do not leave the engine running when you check the radiator fluid level, and do not ever attempt to check the radiator fluid level when the engine is hot.
2. 2
   Raise the hood.
3. 3
   Look for the radiator cap. The radiator cap is a pressurized cap near the top of the radiator. Newer cars label the cap; if yours isn't so labeled, check your owner's manual to find it.
4. 4
   Wrap a rag over the cap and remove it. The radiator and overflow caps absorb engine heat from the coolant; using a rag protects you from being scalded.
5. 5
   Check the level of the radiator fluid. The coolant level should be near the top. If there is any sort of "Full" marking etched into the radiator metal, that is the level to where your coolant should be.
6. 6
   Find the cap to your radiator overflow tank and remove it. In addition to the radiator tank, most modern cars have an overflow tank for the radiator fluid to expand into when it gets hot. You should normally find very little fluid in here, if any. If your coolant level is low in the radiator and nearly full in the overflow tank long after the car has been driven, take the car in for servicing at once.
7. 7
   Check the freezing and boiling point of your coolant. Over time, the ability of your radiator fluid to absorb and dissipate heat declines. You test the freezing and boiling points with an antifreeze hydrometer. See the directions under "Checking the Coolant's Protection Level."
8. 8
   Add coolant as needed. Add the fluid to the overflow tank if your car has one; otherwise, add it to the radiator. (You may want to use a funnel to prevent spillage.) Under most driving conditions, antifreeze should be mixed with distilled water on a 50-50 basis. In more severe climates, you can go as high as 70 percent antifreeze to 30 percent water, but no higher.
   • Do not add fluid while the engine is still warm.

Checking the Coolant's Protection Level

1. 1
   Squeeze the hydrometer bulb. This forces air out of the hydrometer.
2. 2
   Insert the hydrometer's rubber tube into the coolant.
3. 3
   Release the bulb. This draws coolant into the hydrometer, so that it floats either the needle or plastic balls inside the hydrometer.
4. 4
   Remove the hydrometer from the coolant.
5. 5
   Read the freezing/boiling point level on the hydrometer. If your hydrometer uses a needle, the needle should point to either a specific temperature or temperature range. If it uses a series of plastic balls, the number of balls that are able to float indicates how well your antifreeze protects the engine from freeze-up or boilover. If the level is insufficient, you'll either need to add coolant or replace it entirely.
   • You should test the coolant protection level in the spring and fall, and more often if you drive the car under extreme conditions.

   
   

Tips

• While the terms "antifreeze" and "coolant" are used interchangeably, properly "antifreeze" refers to the product mixed with water, and coolant refers to the mixture.
• Most antifreeze is chartreuse or green in color. Extended-life antifreeze, however, is orange or red in color. The difference between regular and extended-life antifreeze, apart from the color, is the amount of rust inhibitors and other additives it contains.

Warnings

• If you notice fluid underneath your car matching the color of its antifreeze, or notice a sulfurous smell, hear a whistling sound or the temperature gauge goes up and stays up when you drive, take your car in for servicing immediately.
• Most antifreeze contains ethylene glycol, which is toxic to humans and animals. Old antifreeze should be disposed of properly.

Things You'll Need

• Antifreeze/coolant
• Distilled water
• Antifreeze hydrometer/tester
• Rag
• Funnel (optional)
• 
  

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