Engine overheating is a problem that can occur at any time and on any vehicle, no matter the make or model. A leak in the cooling system or a faulty radiator and an opaque white smoke will suddenly start coming out of the hood.
Such a failure can have dramatic consequences on the engine so we created a quick guide to help you better understand why your engine is overheating, what you can do about it and when you should have the vehicle checked by a professional.
What is engine overheating?
During operation, an engine heats up because of the combustion that takes place in the cylinders and all the friction created by the pistons going up and down. It’s the coolant system’s job to keep all that heat under control.
If a cooling system failure or combustion problem occurs, heat will instantly rise and build up inside the engine ultimately causing engine failure or a seized engine. This phenomenon is called engine overheating and it’s definitely not a good thing.
How does the cooling system work?
On most vehicles, the engine’s temperature is regulated by circulating a 50/50 coolant/water mix through special cooling passages.
A water-cooled engine block and its cylinder head are interconnected to cooling channels passing through them. At the top of the cylinder head, all channels converge to a single outlet port.
A pump, driven by a pulley and the crankshaft belt, pushes the hot coolant towards the radiator.
The airflow passing through the radiator absorbs excess heat and the cooled down liquid then returns to an inlet at the bottom of the block and starts over the cycle again.
In an engine at its normal operating temperature, the coolant is kept just below the boiling point. To increase the boiling point of the coolant, a radiator cap equipped with a pressure valve is required. When excessive internal pressure is reached, the valve opens. The coolant flows through an overflow pipe leading into an expansion tank. From there it is sucked back into the engine when the coolant cools down after the engine turned off.
What is the radiator fan doing, then?
The radiator needs a constant flow of air through the core to cool it efficiently. When the car is in motion, it cools down naturally because of the constant air stream. But, when it’s idling or standing still, a fan is used to help with the airflow.
Most recent vehicles are equipped with an electrical fan and temperature sensors. However, older models used to have a viscous clutch system worked by a temperature-sensitive valve. It allowed the fan to work its magic until the temperature of the coolant is back to normal.
Most common signs that your car is overheating
In the event of engine overheating, the first thing you’ll obviously notice is the temperature rising on the temperature gauge. Sadly not all cars are created equal. Some of them aren’t equipped with a temperature gauge so a red light could light up in the instrument cluster instead of letting you know that. It’s already too late and the car is already overheating. Not the best system, I know, but it’s still a thing.
The ideal temperature for an engine is around 90°C. The needle should remain in a range of plus or minus 10 ° C for optimal operation.
A coolant smell inside the cabin could also be a good pointer. When coolant is leaking, it sometimes burns when in contact with the exhaust system, creating a sugary smell inside the car.
Sudden greasy windows can also mean something is leaking somewhere. When the heater core is leaking inside the ventilation ducts, a greasy fog will appear on the inside surface of the windows.
Most common causes of engine overheating
Lack of coolant
Engine overheating is more often than not the result of a lack of coolant in the circuit. If there is not enough liquid inside the system, the circulation is much worse than it’s supposed to and the coolant won’t be able to dissipate the heat as quickly.
To add to the problem, when the coolant in the engine and the hoses are lower than required, air will fill the empty space. It will cause the coolant’s temperature to rise even quicker, creating a chain reaction, causing the temperature to rise exponentially.
Obviously, dirt, rust, and grime getting inside the engine or building up inside the radiator will gradually reduce. It ultimately brings the coolant flow to a halt, preventing it to do what it’s designed to do.
Broken radiator fins can also significantly reduced how efficient a radiator is. Maybe not to the point of causing engine overheating, but it will definitely run hotter than intended and will surely not help it keep the temperature down.
The latter is the central component of the coolant system. It has the role of allowing the coolant to flow in a smaller circuit when it is cold to heat up the engine as quickly as possible for better fuel efficiency and to reduce cold start wear to the engine.
When it is hot enough, the thermostat then opens the small circuit on the big one so that the radiator can take care of the rest. A faulty thermostat may remain shut off and prevent hot coolant from reaching the radiator. Overheating will occur very quickly if it’s the case.
Faulty water pump
In the same idea, if the coolant no longer circulates in the circuit then there is no colling anymore. The coolant will stagnate and heat up indefinitely. Note that an incorrect adjustment of the drive belt will logically wear out the bearings of the pump. So in that case, the belt would be the cause of the overheating, but you get the point.
Worn out belt
An accessory belt that slides freely or is simply cut off will certainly not be able to drive the water pump at its full efficiency, reducing or even preventing the flow of coolant fluid into the system. Of course, a completely sectioned belt will generate several other rather obvious symptoms.
It should be noted that some engines have a water pump driven by the timing belt or a timing chain. In such a case, a broken belt wouldn’t cause engine overheating even though it would still bring the car to a halt in a short period of time.
Low oil level
An engine running dry, i.e. with an incorrect oil level, will definitely end up overheating. An unlubricated metal-to-metal contact between component produces a lot more heat than usual and will quickly overcome the radiator’s capacity to dissipate heat.
Dry engines usually burn or seized really quickly. Make sure you don’t drive your car improperly filled with oil or overheating for a long time. If you do, you’ll probably have to replace the whole block.
Burnt radiator fan motor
If overheating occurs only in hot weather, the fan that is supposed to help with cooling is probably not working properly. In any case, if your temperature gauge is in the red and the fan is not turning at full blast already, it’s most probably burnt.
Burnt thermal switch
A thermal switch is what is turning the radiator fan on and off. If it’s burnt, it will simply stop sending power to the fan, which will appear like it’s broken even if it’s not.
This one is a rare occurrence these days tho. I don’t know why but manufacturers seem to have found a way to make more reliable thermal switches than before.
Damaged cylinder head gasket
Probably the worst case on this list, a damaged cylinder head gasket will require the engine head to be removed for inspection. Nothing cheap here!
In the case of head gasket failure, two scenarios can happen:
- The coolant will leak into the cylinder and will cause the engine to produce a white smoke coming out of the exhaust system. The coolant level will go down with time and may cause overheating. Your ignition system may also have a hard time to produce sparks to ignite the fuel in a wet environment. This scenario will probably cause misfires and engine stalls.
- The oil will leak into the coolant system, creating a thick peanut butter-like slime. This slime will boil quicker than coolant would, allowing air to infiltrate the system and cause overheating. The buttery liquid will get literally everywhere, coming out of the expansion tank and out of the radiator cap. Radiator hoses may pop out and create leaks to the heater core. A real nightmare.
How to deal with engine overheating?
There’s no quick answer to that question. It always depends on how bad the situation is, what are the symptoms and where you are when it happens. You won’t be able to drive that far if the temperature is stuck in the red.
If the condition has just started and the temperature is just a little higher than usual, it’s a different game. Being stuck in traffic with no ability to drive faster or driving where you simply can’t pull over, can be pretty challenging too.
If you can safely pull over
The first thing to do when your engine starts overheating is pulling over to the side of the road. Turn off the engine as soon as you can but leave the ignition to the RUN position. This will allow the radiator fan to stay on to help cool down your engine as quickly as possible.
When an overheating engine is turned off, the crank will stop driving the water pump and the circulation of coolant will stop, creating a sudden rise in temperature. If the temperature was already in the red, the sudden heat spike could create an engine seizure. And you don’t want that.
Open your hood and look for smoke coming out of somewhere. Make sure the level of coolant in the expansion tank is where it should be at. If the coolant is flowing out of the tank or boiling inside of it, do not open the system! Wait until the temperature of the car is back to normal, top off the coolant level and try starting your engine again.
Overheating is rarely an intermittent condition so your engine will most probably overheat again. The goal here is to safely bring your car to wherever you want to get it fixed. If a radiator hose is blown out and there’s no more coolant in the system, there are not many things to do. You won’t be able to drive that far with an engine working without a cooling system.
You’re better off calling a tow truck right away and make sure you don’t end up with a seized engine and having to replace the whole thing. Same for a broken belt. The car will probably stop moving way before it overheats anyway because of the lack of a working charging system.
If there’s still coolant in the expansion tank and the temperature goes back to normal, the trick here is to drive while keeping an eye on the temperature gauge and turning the engine off when it gets in the red, let it cool down and start over again until you have reached your destination.
Common sense is required here. If you still need to drive 200km to get your car fixed, that solution may not be suitable for you. When in doubt, just get your car towed to the nearest garage. It will prevent this problem to turn into an even worst and more expensive one.
If you can’t pull over
If you are driving on a road where there’s simply no place to stop, the best thing to do is to turn off your A/C and turn up the heat to the max. Drive as fast as you can until the temperature hits the red and hope for the best. Turning on the blower will help to cool down the coolant inside the heater core. It will definitely not be as efficient as the radiator would but it’s better than nothing.
Driving faster will also help to bring more airflow to the radiator. It should also help a bit but a faster running engine will also produce more heat so it brings mixed results. The main idea here is mostly to go as far as you can in the least amount of time.
Here’s a pretty neat trick. Turn off the engine at top speed. Put the transmission in neutral. Then, let the car go as far as it can without having the engine running.
An overheating engine while being stuck in traffic is probably the worst scenario possible. Unless it’s also located in a construction zone with only 1 traffic lane left while butter juice is blowing out of your radiator.
In such a case, there’s nothing more to do than to turn the key back to the off position. Put the hazards on. Go sit on your hood and wait for the tow truck to come to rescue you. Try not to get killed by the angry driver stuck behind you. It happened to me once and it was definitely one of the worst days of my life.
How to prevent overheating
Preventing faults in the cooling system is not an easy thing to do. A leaking water pump or damaged head gasket is hard to see coming in advance. Your best bet is to keep the component in good working condition and to make sure you get your car inspected by a certified mechanic regularly.
Belts need to be replaced as soon as they crack or start making that irritating screeching sound. Coolant also needs to be replaced according to the manufacturer’s specifications. If not, it can become acid with time and it will gradually wear through various components like heater cores and water pumps.
Make sure they look out for rust at the bottom of the radiator. Also, look for small cracks on hoses and replace faulty components before they cause problems while you are driving.
Certified mechanics already look out for signs of an aging cooling system while doing inspections so if your car is inspected frequently you shouldn’t worry too much about overheating.
Constantly keeping an eye on the temperature gauge while driving and making sure fluid levels are correct is probably your best bet to prevent any unfortunate overheating problems. It happens when you least expect it. In the worst possible scenario. So save yourself a good headache and keep your cooling system as sharp as you can at all times!