How to Get Oil Out of Your Vehicle's Coolant System

A sign that says "engine coolant only."
What You'll Need
Drain pans
Dishwashing liquid or dishwasher detergent

A leaking gasket can lead to oil in the coolant system of your vehicle. You’ll know there's a problem when you look at the coolant because the oil will be a different color and will be floating on top of the coolant. When you see this, you will need to remove the oil from the coolant system as soon as you can before it does any lasting damage. Although the task is easy, it will take some time and effort to complete.

Step 1 - Prepare the Car

Remove the radiator cap and open the top of the overflow bottle. Start the engine and keep it on a low idle until the engine has warmed up. Now, take ¼ cup of dishwashing liquid. You’ll need to choose one that doesn’t contain 4-D Butyl Ester since this could react with the materials in your head gasket and ruin it.

You can also use dishwasher detergent which will foam less. If you use dishwasher detergent, you should use about ½ of a cup. Pour the detergent into the overflow bottle so it starts to foam. Don’t be worried — this is to be expected.

Step 2 - Flush the Oil Out

Open the valve at the bottom of the radiator, making sure you have an empty drain pan underneath. You’re going to need a number of drain pans. Keep your engine running for the entire procedure. Turn on your hose and point the nozzle into the overflow bottle. If you have an older car, you’ll need to point the nozzle directly into the radiator. You don’t need a hard flow from the hose, just enough to make sure you replace the coolant coming out of the drain plug of the radiator.

Step 3 - Clean the System

Be aware that your coolant system is going to be foaming for quite a while as the detergent works its way through. Keep running the hose all the while, replacing the drain pans when they become full and putting the contaminated coolant into sealed containers so you can dispose of it responsibly later. On no account should you let the coolant just drain into the earth, since it’s highly toxic and can cause pollution.

When there’s no more foam coming from your coolant system, turn off the car engine and close the radiator drain plug. Keep the water running from the hose until the coolant system of your vehicle is full. Allow the water to sit for several minutes and make sure the drain pans are empty.

Step 4 - Refill the Cooling System

Start the engine again, turn the hose back on and open the drain plug so you can flush the system again. This will remove the last of the oil. Turn the engine off and allow the water to drain out. Close the drain plug.

Now your cooling system is clean again and you’re ready to refill it. Use a mixture that’s 50 percent coolant and 50 percent distilled water. Make sure you use distilled water and not regular water from the faucet or hose.