Main image for post: Winter Car Care: Why Won’t My Car Warm Up?

It’s freezing. Has anyone else noticed? And there’s nothing worse than when your car simply won’t warm up on a winter’s morning… Well, except for waiting for the bus in the snow.

How does the heating work?

The heating in your car is supplied by hot coolant that circulates through the engine. A small amount of coolant is diverted into a hose that eventually reaches a heat exchanger or heater core. Cold air from outside, or recirculated air from inside, is directed through that heater core, until it becomes warm and blasts through your vents, making the cabin nice and toasty.

Unfortunately, if your heater isn’t working, there’s loads of things that could be causing the problem. Today, we’ve listed a few of the most common ones to help you find the answer.

Low Coolant Level

Although a weak or leaky radiator can often be the issue, if your car’s cooling system is not completely filled then this would be the culprit to no heating. Check your coolant levels per your manufacturer’s guide to see if your car’s radiator is full.

Air Pockets

Another common culprit to this problem is air pockets in the heater core or hose that can interfere with the flow of coolant. You can check to see if the coolant is circulating through the heater core by feeling both heater hoses. Both the inlet and outlet return hoses should feel hot when the engine is at normal operating temperature and the heater is on.

Open Thermostat

An open thermostat could also be the problem, or one that’s too cold for the system. Most modern cars need a thermostat that’s 87-90-degree C. It’s quite straightforward to check if the thermostat is open.

Start a cold engine and feel the upper radiator hose. You shouldn’t be able feel any warm coolant moving inside the hose until the engine starts to get warm. After several minutes, you should feel a sudden surge of hot coolant when the thermostat opens.

Blocked Heater Core

If debris builds up in the cooling system, this can plug the heater core and block the flow of coolant. Unfortunately, the only fix is to replace the heater core itself.

You can prevent the problem from happening again by flushing and refilling the cooling system with a fresh, 50/50 mixture of water and antifreeze. Where you can, use distilled water as it contains fewer minerals

Weak Water Pump

Don’t forget about a weak water pump – if your heating’s not working this could definitely be a possibility. A pump with corroded impeller blades or one that doesn't turn fast enough because of a slipping drive belt will certainly leave you in the cold.

Stuck Fans

You’ll know if your fans are stuck because they’ll make a loud roaring sound at high speeds. Your radiator might also be over-cooled. Check the electric cooling fan and clutch fan to see if they are stuck.

Faulty Heater Control Valve

On most modern vehicles, vacuum-operated heater-control valves are normally open - unless vacuum is applied. This allows coolant to circulate through the heater core, even when the heater isn't being used.

A mechanic can check the control valve by applying a vacuum with a hand pump. If the valve fails to close, it will need replacing.

Electrical Problems

If your blowers aren’t working, or if there is no sound or air coming from the system, the motor might be broken. Electrical problems include blown fuses, a defective power relay, heater switch or resistor, or loose wires – all of which should also be checked.

Always be careful when checking hoses and fluid levels because, although your car might not be, coolant can be very hot. If you’re not 100% confident with checking any of these, always take your car to a professional. Give our Car Service Centre a call and one of our friendly team will be happy to help – and get you on the road to a warmer car for winter!