How Long to Wait Before Adding Coolant

How Long to Wait Before Adding Coolant

In your car, there’s a coolant temperature sensor that works with antifreeze coolant to help your engine perform efficiently. When you start to drive your car, the engine goes through combustion. Combustion is the process of releasing energy from the fuel and air mixture. The fuel and air mixture is dictated by the PCM and this gets information from your engine coolant temperature sensor and the Intake air temperature sensor. In order for the coolant temperature sensor to send the right signal to the PCM, the right amount of coolant needs to be added to your car.

In order for you to add coolant to your car, you need to open the coolant reservoir and pour the coolant in. This allows the coolant thermostat sensor to measure the temperature of the coolant. This temperature is then sent to the engine control unit and the car’s computer will use the temperature information to continue operating or to adjust certain functions and keeps the engine working at a good temperature. This also allows the PCM to ensure that the air-to-fuel ratio is mixed right.

If your coolant dashboard light turns on letting you know that the engine has reached its temperature limit, then you’ll need to pull over and put the right amount of coolant in the reservoir. If you’ve been driving for a while, chances are your engines hot and you’re worried about pouring in the coolant too soon. So how long should you wait for your engine to cool down below you pour the coolant in the reservoir?

How Long to Wait for Engine to Cool Down Before Adding Coolant to Reservoir?

After driving with a hot engine, you should wait between 2-3 hours before you open the coolant reservoir cap and pour coolant into the reservoir. When your coolant is warm, it’ll show a false high reading due to expansion, so wait for a few hours for the engine and radiator to cool down so you can see the true capacity of the coolant and enter the right amount.

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If your coolant light started to illuminate whilst you were driving, having to wait 2-3 hours can feel incredibly long just to wait for the engine to cool down before you open the reservoir cap. When you stop driving, the engine doesn’t cool down straight away. Residual heat from the engine can circulate the whole bonnet pass through to the reservoir. If your car been driving for a while, and the water pump and fans have stopped running, which happens to most cars, this means that there’s no significate airflow that’s going on within the engine and radiator.

You can still wait for 30 minutes to 1 hour after you’ve turned off your car to pour the coolant into the reservoir, but it’ll still be warm. It’s not hot enough that you can’t take off the cap, but it’ll still be warm. This means that the coolant reason may be slightly incorrect due to expansion and you might end up pouring the wrong amount of coolant.

The danger of opening the radiator cap when the coolant is still hot is that it could blow hot stopover your face. When taking off the cap, chances are you’re directly over it and this can cause the steam to burn your face or hand. You may also get some oil on your hands if you end up taking the cap off too soon. Even if you can take off the cap whilst its hot, if you pour the cold coolant into the hot cylinder block, this can end up cracking the block or the heads in a worst-case scenario.

How to Know When Coolant Reservoir is Cool Enough

There are a few ways to know when the coolant reservoir is cold enough for you to take the cap off and pour the coolant in. The first way is by you waiting a long enough time. If you wait long enough, you’ll know the reservoir can be opened without you hesitating. Usually, this is when you’ve managed to turn off your car and you’re able to go home and chill whilst the cap is cooling down. After a few hours, the reservoir will be cool enough to be touched and have coolant poured down it.

Another way to tell if the reservoir is cool enough is by gauging whether the reservoir is cool or not. You can do this by tapping the metal that’s neat the reservoir and getting a feel of whether it’s too hot or not. When doing this, make sure not to touch any plastic or rubber that’s close by because it’ll feel a lot more different compared to the metal. You can also use a towel to feel the top of the cap and this will allow you to gauge whether the reservoir is cool enough to have coolant poured down it. If you feel that it’s cool enough, then you can open the cap with the towel to protect your face and hands from the steam. When doing this, make sure to only open it by doing little turns at a time. This way, the pressure will be eased out slowly rather than rush out all at once.

The last way and the most accurate way to tell is if the coolant level has reached the cold fill line. This line indicates that the engine is cool enough, as well as the reservoir and that coolant can be poured down it. If the coolant hasn’t reached this line, then avoid opening the cap and pouring coolant down it.

How to Top Up Coolant Once Reservoirs Cool Enough

Before you start to think about pouring your coolant into the reservoir once it’s cool enough, you need to find your vehicle’s manual and check the correct engine coolant’s that can be used it. Once you’ve done this, you need to buy a gallon of the correct coolant (View on Amazon).

Roll up or remove any loose clothing and keep them away from the cooling fan. Sometimes fans can turn on automatically even when the engine is turned off. Make sure not to remove the coolant reservoir cap until it’s cool enough. You can ensure this by waiting a few hours. Put a towel or a thick cloth on the reservoir cap as the cap can be under pressure and blow steam onto your hand.

  1. Make sure your vehicles in or Park or Neutral and the parking brake is set.
  2. Open the hood of your car and find the coolant reservoir. This is usually a see-through white tank that has a hose that connects to the radiator.
  3. Make sure the coolant is up to the cold fill line. This will indicate that the engine is cool enough.
  4. Loosen the reservoir cap with the towel on it and loosen the cap slightly allowing the pressure to be released before taking it off completely.
  5. If the coolant level is too low, then add the correct amount of coolant. If you have a diluted coolant, you can mix it with water making sure the ratio is 50/50 to create your own coolant mix.
  6. Once you’ve filled the coolant to the cold fill line, then you can tighten the cap and shut the bonnet.

How to Fix Low Coolant

Your vehicle’s systems are able to cool down because of the coolant. If you want to make sure that the cooling system is working properly, you need to make sure that the coolant in there is functioning properly. If you’re having to top up your coolant, it’s a sign that there’s a leak somewhere as you should never really have to replace your coolant. If your coolant is leaking, you have failed to maintain your vehicle and now you’re experiencing problems. The main cause linked to low coolant issues is a failure to maintain your vehicle.

If you want to avoid coolant leaks, coolant problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.

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Signs of Low Coolant

Before you even start to fill up your coolant reservoir, there are signs that will indicate to you that the coolant is too low. It’s best that you know these signs to prevent heat damage to your engine. Failure to recognize these signs and provide your car the right amount of coolant when needed can lead to the engine overheating which will affect its longevity.

Temperature Gauge Going towards Red – if you’re driving and you notice that the temperature gauge needle is going towards the red, this is the first indicator that the cooling system is not working as it should do. This can be a sign the coolant level is too low and you’ll need to top it up. To fix this, you can open the bonnet, and this will cool down the engine slow. From here, take the necessary steps to find the cause of the problem.

Decrease in Fuel Economy – If you’ve noticed a decrease in fuel economy, this can be because of a low coolant level which can affect the CTS. The sensor sends information to the engine control unit which in turn sends a signal back and this makes sure that the engine fuel mixture is correct and allows for maximum fuel efficiency.

Black Smoke from Engine or Exhaust – if there’s black smoke coming from your engine or the exhaust pipe, then this can be a sign of a low coolant level. This can happen if the PCM is unable to mix the air-to-fuel properly because the coolant was unable to remove heat from the radiator and therefore the Coolant Temperature Sensor didn’t give it the right signal.

Increased RPMs – if you’re driving and you notice that the engines RPM has changed suddenly, this can be because of a low coolant level. If the CTS is providing the PCM the wrong signals because the coolant is too low, this can give the combustion system the wrong fuel to air mixture. Therefore, the engines RPM can suddenly increase when it’s warmed up which can lead to the engine being exhausted.

Engine Overheating – If you notice that your engine is getting excessively hot, then this can indicate that there wasn’t enough coolant to cool down the radiator. This can be caused by an incorrect air-to-fuel mixture which can be due to the Coolant temperature sensor sending the wrong information to the control unit. An overheating engine can lead to long term damage to your engine and the complete shutdown of your car.

Check Engine Light – if your check engine lights come on, this can indicate that the coolant level is too low. The check engine light is triggered when the engine control unit can’t regulate or maintain a problem with your car. The downside to using this as a symptom is that the check engine light can come on for loads of reasons. If you want to know for certain this is why your check engine light came on, you can check it using an OBD2 scanner (View on Amazon) to diagnose this.

Is There a Time That’s Too Long to Wait

If you’re wondering if there’s an optimum temperature for the coolant to be added, or if you’re worried that the engines to cool for the coolant to work when your start driving again, don’t worry. The cooler the coolant reservoir the better. If you risk touching the cap when it’s too hot, it can lead to burns. Even leaving your engine overnight to cool down is better than waiting a few hours or even 30 mixtures. After a few hours, there’s still going to be some heat pressure on the reservoir which can cause it to blow hot steam.

Can I Put Anti Freeze in There?

Make sure that you’re putting coolant into your coolant reservoir and not anti-freeze. If you only have anti-freeze, you can mix it with 50 parts anti-freeze and 50 parts water. If you want to confirm this ratio, you’ll need to look at your owner’s manual.

Job Guthiri is a freelance writer with 3 years of experience writing for Motorsrun and other established automobile outlets. His focus and key interests are Tacomas and maintenance. Read our Editorial Guidlines and Fact Checking process.