The cooling system is one of the components of your vehicle that is necessary for it to work as well as it can while preventing serious problems that can occur. An improperly cooled vehicle runs the risk of overheating which can bring with it incredibly high repair bills as well as serious damage and malfunctions. The last thing you want to do is have to have your whole engine replaced because of extensive damage from running too hot. Keeping your cooling system running properly is therefore pretty important, and that means you need to keep an eye out for the problem of air in the cooling system. When this happens, it greatly diminishes the overall ability of your system to stay at the right temperature.
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How Does Air Get in the Cooling System?
There are a couple of ways that air can get trapped in the cooling system of your vehicle. These are all things that you can be on the lookout for to test it if you have air in the lines in need to have them blood to repair the problem.
Faulty Radiator Cap: If the radiator cap isn't sealed correctly, then there's a chance that air is sneaking into the line. The radiator cap needs to be closed and pressurized to work properly. If it's not sealed exactly right, cool it will escape and air can get into the line.
Blown Head Gasket: The head gasket seals the cylinder head of your vehicle. If it is worn down in some way either from exposure to heat or general wear and tear, the seal can be broken, and air can get in.
Radiator Hose Leak: Any hose in your vehicle is subject to wear and tear over the life of your vehicle including in terms of radiator hoses. Over time, due to exposure to heat, or even faults in design, these hoses can form small cracks that allow coolant to leak out and are to seep in.
Bad Coolant Refill: It's possible that if you're refilling the coolant in the tank, or if you flushed it incorrectly as well, the air could have been trapped in the system that will need to be flushed out a second time. This is the easiest problem to fix out of all the ones listed, as nothing actually needs to be repaired in this case. All you need to do is bleed the line and then refill it properly to ensure there are no air bubbles.
Signs of Air in Your Cooling System
There are a few signs you could be on the lookout for that you have air in your cooling system that can give you an indication of where to look when it comes to getting the problem fixed. When you have air in your coolant system, it causes steam pockets in the line which act almost like plugs preventing the coolant from continuing to flow. That's why you end up with your engine overheating, because the coolant isn't allowed to continue through or it moves very slowly. Once the air pocket is able to move out of the way, then the coolant can start working again and the engine will cool down. Unfortunately, this will continue to happen until it gets fixed. Anytime that the coolant system gets open air will be in there, so you'll need to properly purge it each and every time.
Overheating After Repairs
If your car has not had any issues with overheating before taking it into a garage to get some work done, especially if you had something like the water pump, the radiator, the heater core or coolant hoses looked at, and now you're experiencing overheating in your engine there's a good chance that something is either cracked, loose or improperly secured and that has led to air in the line.
Inconsistent Overheating
This happens when your vehicle starts to overheat, and then seems to even out on its own without you having done anything to prevent or address the problem. This is a result of the air bubbles leading to an overheating situation, and then coolant flowing through the line afterwards to get the temperature back down to where it's supposed to be. This will continue to happen as air in the coolant cycles through the lines at random.
Poor Heating from Your Vents
If it's cold and you're trying to keep your vehicle warm, you'll notice that the air blows warm sometimes and not other times. This is a symptom of the coolant system having air in it.
Fluctuating Idle
If your vehicle at idle seems to have problems that aren't consistent with the rough idle that you might get from engine misfires, as in it seems to idle up and down unpredictably, then there's a good chance that you have air trapped in your coolant line somewhere.
How to Get Air Out of Your Cooling System
If you have air in your cooling system you need to bleed it in order for it to start functioning properly again. Bleeding removes the air pockets and prevents not just overheating but the repercussions of overheating such as potential cracks or warping that can occur in the engine. An engine that has overheated for too long can end up being a massive repair bill down the road.
There are several different ways to bleed the air out of your cooling system and a lot of it depends on the make, model, and year of the vehicle that you have. Some cars have something called a bleeding screw that you can use which makes the process really simple. Not every car has that though, so if you're not sure you can check your owner's manual to find out.
Bleeding a Cooling System with a Bleed Screw
If your car has a bleed screw will be located near the top of the engine. As we said, you can check your owner's manual to find out not only if your car has one but where it's located. Usually it's on the thermostat housing by where the radiator hose connects to the engine. It should just be a single screw visible in that location. You never want to try this when your car is still hot however, so make sure it's been sitting long enough to cool down to reduce the risk of physical damage or burns.
You can start the process by removing the radiator cap. Top up any coolant that is leaking out of the system to the mark listed in the coolant tank reservoir. When you're finished, replace the radiator cap.
With the radiator cap secure, put a pan or some other kind of container under the engine so that any coolant that leaks out will be caught. You don't want this to pollute ground.
Start your engine and let it idle for 15 to 20 minutes until your car is up to temperature. If you're not sure, you can check the radiator hose and it should be hot to the touch. When your engine is at temperature you can turn the bleed screw one or two turns counterclockwise. You don't want to remove the screw, just losing it. Taking it out completely could result in a burn.
Once you loosen the screw the coolant will start flowing out. At this point it should have bubbles in it indicating that it does have air. let it continue to flow out until it's coming out in a solid stream rather than any with bubbles in it. Once all the air bubbles are bled out you can re-tighten the screw and then wait for the engine to cool down.
At this point you can add some more coolant to make up for what's leaked out and then give your car a test drive. At this point it should be working at normal temperature. If not, you may need to have a more in-depth bleed or take it to a mechanic.
How to Bleed a Cooling System with No Bleed Screw
If you don't have a bleed screw, then there is another method that you can use to get rid of the air in your line. As with the other method, you want to make sure that your car is cold to start so that you don't injure yourself.
Again, remove the radiator cap and fill the coolant tank with the mix of coolant and distilled water up to the bottom of the radiator neck. Also add the coolant to the reservoir up to the mark indicated. With the cap off, restart the engine. Once it's up to temperature you'll be able to see the coolant flowing in the tank. Once you've let the coolant flow for a few moments it will have purged all the air from the system. At this point you can turn off the engine to let it cool down. Now you can add more coolant to get it to the correct level if you need to and give the upper radiator hose a squeeze to get any additional air out.
Replace the radiator cap and start the engine again to get it up to temperature. Give the car test drive and see if the temperature stays cool or if it begins to overheat.
Bleeding a Cooling System with Jack Stands
For a thorough bleeding of your cooling system you're going to need to use jack stands to get under your car. As always, make sure the engine and radiator are cool and use a floor jack to get your car lifted up to the point that the radiator neck is above the engine. Secure the vehicle with a jack stand at this point on each side and block the rear wheels. It's also a good idea to set the parking brake.
You want to remove the radiator cap and start the engine as with the other methods and get the car up to temperature. As before, wait for the engine to run for a few moments until the air has been expelled from the system so that you can turn off the engine.
Let the engine cool down and add more coolant until you're at the correct level. Give the upper radiator hose another squeeze to get any trapped air bubbles removed and then top up the coolant if necessary. Replace the cap, lower the vehicle back down, and take it for a test drive.
At this point your car should definitely have been purged of any air in the lines. If none of these methods work, and you're still experiencing the same problems, then you may need to go to a mechanic to get to the root of the issue. It's likely that you have a different issue altogether that you're dealing with or there is a crack or break somewhere in the cooling system but still allowing air to get in.
The Bottom Line
Having air in your cooling system is not all that uncommon, but it is definitely something that you need to take care of as soon as you realize it's an issue. As we said, if your engine overheats it can cause some serious damage. Most people don't think an overheated engine can be all that bad, but if you end up warping cylinders or valves because of consistently high temperatures, the cost to repair this can end up being upwards of $3,000 to $4,000 or even more. That's a remarkably high price to pay for something that could have been fixed much more easily.
Getting your coolant system flushed by a mechanic should only cost you $40 to $50 depending on where you live. The difference is quite significant between what it costs to prevent the problem from happening, and what it costs to deal with it after the fact.
If you're noticing problems that seem like they're related to air in your coolant lines, you definitely don't want to sit on this one for too long and allow the problem to snowball out of control going to something bigger and much more expensive. Get to a mechanic as soon as you can, or if you feel like you're up to the task trying to take care of it on your own with the methods that we’ve outlined.