Your car's engine has oil and coolant circulating through it in very close proximity. The coolant transfers heat away from your engine, and the oil helps keep its moving parts lubricated. Your car's head gaskets play the important role of keeping these two liquids separated. If one of your head gaskets fails, your coolant and your oil will mix together.

Head gaskets often fail when your engine RPMs climb too high since this creates extremely high pressure in your engine's cylinders. The high pressure can blow the head gasket and cause it to immediately fail. Head gaskets can also rapidly deteriorate if your engine overheats. If you think that your car may have blown a head gasket, read on to learn four signs that your coolant and your oil are mixing.

1. White Smoke Comes From Your Exhaust

If you're driving down the road and suddenly notice a huge plume of white smoke coming from your exhaust, you've likely blown a head gasket.  Your engine gets quite hot while it's operating. Oil can withstand these temperatures, but coolant can't. If a head gasket fails and allows coolant into a cylinder, it will immediately burn. This creates a substantial amount of white smoke, which will flow out your car's exhaust.

2. Your Engine Misfires Frequently

Your spark plugs ignite the fuel in your engine cylinders, and coolant in your engine can corrode them quickly. If you have coolant leaking into an engine cylinder, your spark plugs may ignite the fuel late or fail to ignite it at all. This causes your engine to misfire, which can result in pinging or knocking sounds coming from your engine while you're driving. You'll also likely experience uneven acceleration due to your cylinders not firing on time.

3. Your Oil Has a Milky Liquid Floating on the Surface

You can visually inspect your oil to determine if coolant has leaked into it. Open your car's hood and remove the oil cap. Shine a flashlight into the oil reservoir and look at the topmost layer. If there's a frothy milky residue on the top of the oil or on the bottom of the oil cap, you most likely have coolant leaking into your engine oil. The milky residue is the coolant that has mixed with the oil and broken down due to high heat.

4. Combustion Gases Leak Into Your Coolant Reservoir

When a head gasket is broken, some of the combustion gases that are produced when the cylinder fires will float up into the coolant system, rather than flowing through your car's exhaust. You can check for the presence of these gases in your coolant system with a combustion gas detector. They're inexpensive, and you can find them at most auto parts stores.

In order to use it, you attach the nozzle of the detector to the top of your coolant reservoir in order to create a vacuum. After starting your engine, the combustion gases that enter your coolant system will rise into the nozzle and react with a liquid within the detector. If the liquid changes color, it means that combustion gases are entering your coolant system, which is likely caused by a blown head gasket.

If you think that your car may have blown a head gasket, it's important to take your vehicle to an auto repair shop as soon as possible. Coolant entering your engine will damage your spark plugs, and it also prevents your car's oil from keeping the engine properly lubricated. If you continue to drive your car with a leaking head gasket, you may permanently damage your engine. While repairing a head gasket can be complex and expensive, it's much cheaper to replace a head gasket than to replace an entire engine.