How to Remove a Radiator Cap without Damaging Your Vehicle

a radiator cap inside the engine
What You'll Need
Gloves (optional)
What You'll Need
Gloves (optional)

One common task in any auto repair is being able to safely remove your automobile’s radiator cap. Every engine must be kept to a certain temperature to keep from overheating.

The radiator does this along with a thermostat by circulating a mixture of antifreeze and water to maintain a safe temperature (around 195 degrees F in most vehicles.)

The radiator cap, in particular, keeps the entire cooling system under pressure by raising the coolant’s boiling point and allowing the engine to reach even higher temperatures safely.

The cap of the radiator itself is a very important component of the radiator and should be removed and checked occasionally to make sure it is working properly.

Step 1 - Allow the Car to Cool Down

spedometer and temperature gauges on a car dashboard

The radiator’s heat and pressure build up to dangerous levels when a car is running. Serious injury can come from removing the cap from a hot engine. If too much pressure has built up, removing the cap can send boiling water and steam up and out in all directions.

Allowing the car to sit for around 30 minutes will ensure the pressure and temperature has dropped to a safe level before you attempt to remove the radiator cap. Most caps have a clear warning label on the outside of the cap itself warning about this important step.

Step 2 - Remove the Cap

There are two different types of radiator caps that need to be removed in two different ways. The most common is a metal push and turn cap. This cap is typically round in shape with ears sticking out from each side.

To remove this type of cap, push down while simultaneously turning the cap counter clockwise. These caps can be found at the top of the radiator itself or close by depending on the type of engine.

The second type of cap is a round plastic cap used only in radiators that have a remote reservoir of coolant. This type of cap is removed by simply twisting it counter clockwise.

Step 3 - Examine the Cap

a radiator cap removed

Once you have the radiator cap removed it is crucial to inspect the condition of the cap’s interior edge. The rubber disc inside of the cap around the bottom should have no cracks or missing areas at all.

If it does it can allow pressure to escape or even lead to the cap blowing off if it were to overheat. If you notice any of these conditions on the cap you should replace it with a new one. Just make sure that the replacement cap you use has the same PSI rating as the original.

Step 4 - Replace the Cap

The last thing to do is simply put the cap back onto the radiator.

For the push and twist type you must be sure to do both or it will not lock in place completely. For the simple twist type, you only need to twist it back in clockwise to tighten the cap in place sufficiently.

Remove a Radiator Cap FAQ

Can you safely remove the radiator cap?

Radiator caps can be removed but the engine needs to be cool first. Otherwise, the coolant in the radiator could spray out when the cap is removed.

Hot, spraying fluid is a serious burn risk. You could suffer from scald damage if you don't remove the radiator cap when the engine is cool.

Can leaving radiator cap off cause damage?

Driving without a radiator cap will cause damage because the coolant will get hot and boil up and out of the radiator. There will not be enough coolant to actually cool the engine, which can cause the engine to overheat.

An overheating engine can cause serious damage that leads to huge problems.

What should you do before removing the radiator cap?

Before removing the radiator cap, very carefully touch the car engine. Until the engine is cool enough for you to place your hand upon it without feeling pain, don't remove the cap.

Once the engine is cool, put on a pair of safety glasses. You still want to exercise caution when removing caps and working on an engine.

Should I see coolant when I remove the radiator cap?

The radiator is full of coolant when everything is working properly, so you should see this fluid when you take off the cap. If you can't, you are low on coolant.

What happens if you overfill coolant?

An overflow hose is attached to your car's coolant system. Any excess coolant goes into this overflow hose, which ends up in a puddle under your car.

If this liquid comes into contact with electrical wiring in the engine for some reason, this could potentially cause electrical damage.