How to Bleed the Air in Your Cars Coolant System

A very good way to begin draining a coolant system is too jack up your car. Since there are plenty of places within the system which can catch air it is important to make sure the cap or outlet opening is at the highest point possible to allow air to escape (as air bubbles with travel directly upwards and can get caught in the systems various nooks and crannies).

Today's engines are loaded with various objects and components: Cylinder heads, water pumps, manifolds. The two primary heat exchangers radiator and heater are aluminum. Aluminum needs great corrosion protection to survive, and the corrosion protection in green and red antifreeze is used up in about two years.

Now we need to drain the coolant, it is very important to do this properly. The ways you do this can vary from car to car and different manufacturers have different systems and quantities of coolant, for this reason its very important to look at your cars specification and see how much coolant there is meant to be in the system in total, that way you can measure it when its out to see how much is missing if any. The capacity of coolant systems can vary greatly some systems can contain as little as nearly 5 quarts whereas others can use around 18.

Its best to start the process with a cool engine so dont do it just after you have driven your vehicle. First port of call check your pressure cap on the radiator, if it is on and the overflow resevior is easily accessable then remove it and empty the contents. Now before you go pouring this down a drain some places have regulations against disposal of this type of waste so dont pour it down your drain, if in doubt take it to a local garage and ask how to dispose of coolants.

Now you need to open your heater coolant control valve (this varies greatly from model to model and some have very different systems so consult your handbook). With this done locate the plastic reservoir and undo the top and open the drain cock (or disconnect the lower radiator hose - again varies from car to car). This should remove around 45% of the coolant, after this it is a good idea to fill the system with water and run the engine to heat it up then allow it to cool, drain the radiator in the same way again and repeat if necessary. When satisfied leave the system filled with water. No antifreeze.

This is the hard bit: here we need to add half the capacity of the coolant system with anti freeze (so in a 12 quart system you will need to add 6 quarts of anti freeze at this stage). This is were having the car jacked up at an angle comes in handy as it encourages air to leave the nooks of the system and escape upwards.

Many engine have bolts which you can loosen to bleed sections of the system, using your manual locate them and open them, this allows air to leave via these valves. Pour in the required amount of antifreeze slowly until you see coolant oozing out of the open air bleeds. Then close the bleeds and top off the system with the remaining antifreeze and then plain water.

Now you are done, close your heater coolant valve and your done, now one final check: With the engine running at fast idle and warmed up, have someone move the lever or knob which controls your heater coolant valve to hot while you listen at the valve. If after the first rush of coolant you hear a continuous gurgling noise, there's still air in the coolant, and you should be prepared to watch the coolant level in the reservoir over the next few weeks.