Help! There's Air Trapped in My Car's Cooling System

Help! There's Air Trapped in My Car's Cooling System

7th Jul 2016

The cooling system is an invaluable component of modern-day automobiles. It keeps the engine cool by flushing it with coolant. Depending on the car's design, however, air may become trapped inside the cooling system, preventing it from accomplishing this goal. When there's air inside the cooling system, coolant won't be able to reach the critical components of your engine like the cylinder heads; thus, increasing the risk of overheating.

Causes of Trapped Air in Cooling System

So, what causes trapped air in the cooling system and how do you fix it? There are several different possible causes of this phenomenon, one of which is a faulty radiator cap. A car's cooling system is closed and pressurized, with the radiator cap retaining this pressure. If the radiator cap fails, however, coolant may escape and air may enter; thus, leading to trapped air in the cooling system.

In addition to a bad radiator cap, other possible causes of trapped air in the cooling system include the following:

  • Blown head gasket
  • Leaking radiator hose
  • Leaking heater control valve
  • Improper coolant refill or flush

Hopefully, the problem was caused by nothing more than an improper coolant refill or flush, in which case you can fix the trapped air and get back on the road. If it was caused by something else, however, you'll need to identify the root cause of the problem; otherwise, you'll end up repeating these steps multiple times, all the while exposing your car's engine to above-normal operating temperatures.

How to Fix Trapped Air in Cooling System

First and foremost, check to see if there's a bleeder valve on your car's cooling system. Some cars are equipped with a special valve designed specifically for bleeding air from the system. This is the easiest fix for trapped air, involving nothing more than turning a valve.

If your car does not have a bleeder valve, however, there's an alternative method works. Park your car on an inclined hill (or jack it up) so the radiator is higher than the heater core. Next, carefully remove the radiator cap (only do this when the engine is cool to avoid injury) and extract as much coolant from the radiator as possible using a baster or similar suction device. Coolant is highly toxic, and just a couple ounces is enough to kill small pets and animals. So, try to avoid spilling it on the ground. Next, turn the ignition and blast the heater as fast and hot as it will go while the radiator cap remains off. The purpose of this is to flush coolant through the hoses, which in turn should "burp" air from the cooling system. After 15-20 minute of idling, add coolant to the radiator until it's back to normal levels and you should be good to go!