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How to safely check your radiator coolant level

How to Safely Check your Radiator Coolant Level

To keep your cooling system cool, check the fluid level in the system and, if necessary, add water and coolant. It’s dangerous to remove the pressure cap from the radiator or coolant recovery system reservoir while the engine is still warm. Because it’s hard to tell just how hot things are inside the engine, follow these guidelines when removing a pressure cap:

  • Never remove the cap from a radiator or coolant recovery system reservoir when the engine is hot. Adding cold water to a hot engine can crack the engine block.
  • If your engine overheats on the highway, get to the side of the road, turn off the ignition, and then wait 15 to 20 minutes for things to cool down. If you can stay safely away from traffic, you can lift the hood to help the heat escape but you should leave the pressure cap alone.
  • If you’re parked where traffic is zooming by, or if you’re concerned about your security if you leave your vehicle, you’re better off just waiting in the car until the engine cools. If it heats up again when you start driving, get to the nearest service station or a place where you can safely park, get out, and deal with the situation yourself.

Of course, if the engine is completely cold, you face no risk at all, so get into the habit of checking your coolant level at least once a month in the morning before you warm up the engine.

To remove the pressure cap safely, follow these steps after the engine is cool:

Don’t remove the cap on the radiator unless your vehicle has no plastic coolant recovery reservoir, as shown here.


A coolant recovery reservoir (a) and a cap being removed safely from a radiator (b).

  1. If your system has a safety pressure cap, lift the lever on the safety cap to allow the pressure to escape.
    To keep from burning your hand, place a cloth over the cap after you raise the lever. Then turn the cap counterclockwise to remove it.
    If your vehicle doesn’t have a safety cap, place a cloth over the cap and turn it counterclockwise just to its first stop. Turning to the first stop allows some of the pressure to escape, but if you see liquid or a great deal of steam escaping, re-tighten the cap and wait for things to cool down. If nothing escapes, continue turning the cap counterclockwise to remove it.
  2. Tilt the cap as you remove it so that the opening points away from you.
    If there’s still enough heat and pressure to spray hot stuff around, it lands on the engine or inside the hood, where it can do no harm.
  3. Replace the cap by screwing it clockwise. (If you have a safety pressure cap, push the lever down again.)

Radiator safety caps cost very little, so if you don’t have one, buy one! Almost every service station stocks them, but they’re cheaper in auto supply stores. Check your owner’s manual for the amount of psi (pounds per square inch) of pressure in your system and look for the proper number of psi on the new cap. These safety caps are well worth the money.

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