Why Is the Heater in My Car Blowing Out Cold Air and Not Heat?
Now that the cold weather is back, we'll be whacking the car's heater on the second we turn the key. Your car's heaters work by using the heat in the coolant that circulates around the car's engine. That's why you won't get heat until the car has been running for a couple of minutes and warmed the coolant. A thermostat regulates the water circulation; it waits until the water reaches a certain temperature, and then lets the water circulate to cool your engine, and incidentally warm your heater.
To have heat, you need:
- enough water in your engine;
- a working thermostat,
- a working heater and heater controls
- a cooling system that doesn't leak.
If you can't get heat no matter how long you leave the car running, I'm going to show you some checks you can do to find the culprit. If you're not comfortable with mechanics then read still read on so you know what to expect when you take your car to a mechanics. This problem is relatively cheap to fix. Replacing heater matrix's or head gaskets are where the costs become high.
What to Check if Your Car Heater Blows Cold Air
- Is there enough water and antifreeze in the engine?
- Is the thermostat working?
- Is the heating system blocked by an airlock?
- Are the heater controls broken?
- Is there a water leak?
1. Is There Enough Water in the Car?
Your heater uses the heat from the coolant circulating around the engine. You should also have antifreeze in your coolant mixture, this not only stops the coolant from freezing inside your engine but also stops it corroding. The heater is higher up than the rest of the cooling system, and thus last in line for coolant. Thus the first thing you should do, if you have no heat, is to see if there is in fact enough coolant in your engine. You can do this by lifting the bonnet (the hood) and looking at the header tank, which collects overflow coolant from the radiator. This is a large tank, usually clear plastic, with a conspicuous cap, rubber hoses coming off of it, and "Max" and "Min" markings on it. It is positioned a little higher than the radiator, usually to one side or the other of the engine, directly above a wheel. If this tank is empty, you can fill it back up with ordinary water; you can add some antifreeze if you want. If your header tank is full then proceed to the next step. If you are not certain which is your header tank, ask a friend, or take the car to a local garage.
2. Is Your Thermostat Working?
As mentioned before, the thermostat decides whether to let water circulate around your engine. When the engine starts, the thermostat stays off for a while, giving the water a chance to heat up and provide heat for your heater. If your thermostat is stuck, the water may never heat up. So if you have water/coolant topped up, but still don't have heat, a broken thermostat may be the culprit.
To check your thermostat, leave your engine running and watch the dials inside the car. There will be one that indicates water temperature. It can take a while for a working thermostat to be warm enough to give you a reading, so give it about 10 minutes. If after that, your engine is hot, but your temperature dial says "cold," then the thermostat is the reason why you're not getting heat from your heaters. This is a simple fix, and it should be cheap from your local auto shop.
3. Is the System Blocked by an Air Lock?
Sometimes even with water in the system and a working thermostat you can still get no heat; the flow of water in the heating-and-cooling system may be blocked by air or dirt.
One possible cause is an air lock in the cooling system. If your system has a bleed port or bleed screw, and you can find it, you can fix this air lock yourself. Run the engine until the fan kicks in. Once your fan has come on, look around the radiator for a bleed port or bleed screw. This is something that can be turned with a screwdriver. Once you turn it anti-clockwise, you should hear a hiss; this is the air being released.
4. Are the Heater or Heater Controls Broken?
Even though most problems with the car heater are not caused by the heater itself but by the cooling system or the thermostat, it is still possible the heater itself may be clogged or broken. Or the heater controls may be stuck or broken. In either case there is a chance of a cheap or do-it-yourself fix, as shown in the video below.
Toyota Heater and Control Valve
5. Water Leaks? Find Them!
An engine that keeps losing water is a big problem, and not just because low water levels will keep your heater from putting out enough heat. A car that is not gettting coolant will heat up and damage itself permanently. If it leaks water, you need to find the source. It can be a split hose, leaky radiator, the water pump, or even worse, the head gasket. Finding the leak can be a pain in the butt too, as even a tiny hole can let a lot of water out while the system is under pressure from being driven.
But if the weather is cold, that makes your investigation easier. Make sure the engine has run long enough to get good and hot, and make sure the coolant is topped up. Then, if there is a leak, the hot water escaping will turn to steam when it hits the cold atmosphere. Open the bonnet (hood) and look for steam: along the hoses, where the water pump is, and along the radiator. Also look inside your car—if your windows steam up, or the carpet inside the front of your car gets wet, your leak could be inside the car, behind the dashboard. It could be the heater matrix itself (the heater core) or a split hose.
If the leak turns out to be in the radiator, you can save the cost of a radiator, at least for a while, with products that stop leaks in a car's cooling system. You can also buy a repair bandage for leaking hoses, but this is a temporary measure. Hoses are rubber and don't last forever; they have to be replaced every few years.
Sometimes water loss is caused by a knackered water pump. Telltale signs of a broken water pump include a constant rough metallic sound when the engine is running, or water trickling down the side of the engine. The water pump is a vital part of the engine, and if it's broken it needs to be changed as soon as possible. Often it runs off the cam belt ("timing belt"), and if the water pump destroys itself it will take out the cam belt and the engine along with it. Consider replacing an old water pump as part of routine maintenance, along with the replacement of the cam belt and accessory belts, if you have an old car and want to keep it a few years.
A leaking head gasket is the worst news at all; it means your engine has lost its integrity, and your car needs major repairs right away, assuming you want to keep it.
A Simple Trick to Temporarily Fix a Car Heater
Place some cardboard in front of my radiator and behind my front bumper. This is to stop airflow through the radiator, thus heating up your coolant more quickly. If you live in a cold part of the world or have cold winters this hack will help getting you coolant more quickly.
Do not completely cover the radiator. Allow it to get some airflow but use a piece of card sized to restrict a large portion of airflow. This is something I have to do in the winter months. If I don't do this it takes a long time for the coolant to reach its optimum temperature in cold weather, and as soon as I whack the heating on, the coolant temp falls, in part because the air flow is so efficient at cooling the engine.
You can use this simple hack as a temporary measure. Remove the card in the summer months, or if your fans regularly come on. Keep an eye on the temperature needle; if it sits a little high, reduce the amount of card or remove it altogether.