Do You Add Coolant While The Car Is Running?

Making sure your vehicle has enough coolant is one of the most important checks to make when maintaining your car. Coolant may leak over time or be lost through the cooling process. Given that coolant generally needs to be circulated by the engine’s pump, do you add coolant while the car is running?

You definitely should not add coolant to the car while it is running. Doing anything with the coolant while the engine is running could result in severe burns and you also cannot accurately tell the level of coolant when the engine is warm.

I’ll take you through the process of how to check and replace your coolant. I’ll also show you some common mistakes to avoid and tips on how best to put coolant in so that your vehicle is running at peak performance.

Valvoline makes the best antifreeze/coolant on the market. View their products on Amazon here.

Do You Check Coolant While the Car Is Running?

The nature of the cooling system means removing the cap while the engine is running could result in nasty burns. The expansion of the cooling fluid with changes in temperature also means you cannot measure accurately how much coolant is already in the system.

If you’re just checking the coolant level then you should do so when the car is not in a warmed up state. This means you will probably need to wait at least three hours for the vehicle to cool down after it has been running. If the coolant is still warm, it will show a misleading higher volume due to the liquid’s expansion.

The engine should be cool or very close to cool before attempting to remove the cap from the radiator and checking the levels of coolant. You should be able to lay your hand on the radiator without burning yourself before you remove the cap.

Should Cars Be Running When Adding Coolant?

Adding coolant to a vehicle should be done carefully. Cooling systems are pressurized and removing the cap to add coolant when the engine is hot is dangerous. You could get a serious burn from the release of pressure and scalding liquid when taking the cap off. 

Running the motor will heat up the entire engine bay which also means the fill cap itself might be extremely hot to the touch. For your own safety, it’s important to wait until things have cooled off.

After the coolant has been added you may need to run the engine. It depends on the vehicle regarding the next steps that should be followed. After draining the coolant you will either have an exact process to remove air from the cooling system or you will simply run the engine. Otherwise, the pressure of expanding gasses can blow out hoses or radiators. 

How Long Should I Let My Car Run After Adding Coolant?

It is important to circulate coolant through the radiator and so letting the car run for a bit after adding coolant is recommended in most cases. Some vehicles are different and the manual should always be consulted to see what the manufacturer’s instructions are.

Otherwise, once you have added the coolant and started the engine, a few minutes should be enough to circulate the coolant. You can confirm the coolant is circulating by observing it via circulation through the hoses or radiator filler neck.

It is good practice to check the coolant again after running the engine. Be careful that it has not heated up too much when performing this check. The idea is that once the coolant has circulated, you still want to make sure that the total amount of coolant in the reservoir is enough to reach close to the fill line.

How Do I Add Coolant To My Car?

Topping up your car’s coolant reservoir is a simple process and levels should be checked regularly. 

The first step is to make sure you choose the right coolant/antifreeze for your vehicle. Generally, coolants will be able to be mixed so you can just top up your old coolant if it is a bit low. Water is not a substitute for coolant and should only be used in absolute emergencies.

As noted earlier, make sure the engine is cool. Depending on the type, you may need to mix the coolant with water if using a concentrate. The directions on the product should be followed but generally, it is a 50/50 mixture with the other half being distilled water.

Can You Mix Different Coolant Brands?

So called “ready to use coolants” can be added directly to the coolant reservoir.

Next, you need to access the coolant reservoir by removing the cap and adding the coolant. Generally, it’s best to use a funnel and take note of how much coolant is in the bottle before pouring it in. Some coolant bottles come with a clear strip on the side with measuring gauges so you can tell how much you have poured in. 

It is important to know how much coolant your engine takes and then also consider that some extra will be needed to fill the hoses and help prime the pump. Use this figure along with the amount of new coolant you have to avoid overfilling.

Once done, replace the cap and make sure it is securely tightened without overdoing it. As the cooling system requires pressurization, the performance of the cooling system could be compromised if the cap is not put on properly.

Water can be added to the cooling system, but this should only be in absolute emergencies and only if the engine is overheating. This is because water lacks the antifreeze and corrosion-inhibiting properties of automotive coolants. This is doubly so if you live in a cold climate where the water could freeze in hoses or radiators, likely causing irreversible damage.

Valvoline is one the most trusted brands for antifreeze out on the market. View their products on Amazon here.

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