do you add antifreeze with the car running or off?
You can add it with the car on or off, but it is far easier and safer to add it while the car is off because any air movement from the radiator fan can end up blowing the antifreeze around in the air. It is also more likely to spill it while pouring it while the car is on. It is preferable to add it while the car is off, fill it to the proper level, then start the car and let the antifreeze settle into the radiator. You can always shut the car off and add more if necessary.
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