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Never Take a Radiator Cap off a Hot Car: Here’s Why

Centennial Auto Repair

Never Take a Radiator Cap off a Hot Car: Here’s Why

By In Uncategorized On June 05, 2017

Thousands of Americans are severely injured every year one way or another from motor vehicle radiators and coolant. It’s estimated that over three-fourths of these injuries result from removing the radiator cap. Removing the cap on your car’s radiator before your engine has cooled can cause severe burns. Still need a reason to wait for your engine to cool off before you remove your cap? Read on.

Sometimes when driving your car, especially on a long road trip, it may seem  like a good idea to check the coolant level, since  running low on coolant can cause many long and short-term problems for your engine. Almost every modern car has a plastic radiator reservoir that shows the coolant levels just by looking at it without removing its cap.

Take a look at the owners’ manual to find where the reservoir is located. If you’re driving an older car that doesn’t have a reservoir, make sure to always let the engine cool down to ambient temperature before removing the radiator cap. Liquid under pressure can reach much higher temperatures than liquid at barometric pressure because under pressure it boils at a much higher temperature. This is dangerous, because the coolant in a radiator can be over 200 degrees. Also, because it is under pressure, it will shoot out of the radiator and get all over you and your clothing, causing severe burns. The safe thing to do is to wait a few hours after shutting the engine off before removing the radiator cap.

Waiting on the side of the road isn’t the way you want to spend your time on your road trip, but in order to properly check your coolant levels, play it safe and wait until your car’s engine matches the ambient temperature around you. Or, if it’s a hot day, try to cool the engine off in other ways. The professionals would never try to open a radiator cap when the engine’s hot. Be more like the professionals next time you need to check your coolant levels and give it a break before you twist off that radiator cap.