Common Causes of Engine Overheat

Overheating NOTE: To avoid burns and injury, never, ever attempt to remove a radiator cap while the engine is hot!

An overheated engine can be caused by anything that decreases the cooling system’s ability to absorb, transport and dissipate heat; therefore engines can overheat for a variety of reasons.

Let’s take a look at some of the most common causes.

Cooling System Leaks:
This is the primary cause of engine overheating. Possible leak points include hoses, the radiator, water pump, thermostat housing, heater core, head gasket, freeze plugs, automatic transmission oil cooler, cylinder heads and block. Perform a pressure test. A leak-free system
should hold pressure for at least one minute.

Wrong Coolant Concentration Be sure to use the coolant recommended by your
vehicle’s manufacturer. The wrong type of coolant and/or mixing the incorrect concentration of coolant and distilled water can also result in engine overheating. The best bet is to perform a complete flush and fill.

Bad Thermostat A thermostat is a heat-sensitive valve that opens and closes in response to engine temperature. Heated engine coolant passes through to the radiator when the thermostat is in the open position. In the closed position, it prevents the flow of coolant to speed up the warming of a cold engine. When the thermostat gets stuck in the closed position, coolant stays in the engine and quickly becomes
overheated, resulting in engine overheating.

Blocked Coolant Passageways Rust, dirt and sediment can all block or greatly impede the
flow of coolant through the cooling system. This can limit the system’s ability to control engine temperature, which may result in higher operating temperatures and engine overheating. Once again, a flush and fill is recommended to remove debris.

Faulty Radiator By passing through a series of tubes and fins, coolant temperature is reduced in the radiator. Leaks and clogging are some of the most common causes of radiator failure. Any disruption in the radiator’s function can lead to elevated engine temperature and overheating.

Worn/Burst Hoses A hose that contains visual cracks or holes, or has burst will result in leaks and disrupt the flow of engine coolant. This can result in overheating.

Bad Radiator Fan A fan blows air across the radiator fins to assist in reducing the temperature of the coolant. A fan that wobbles, spins freely when the engine is off, or has broken shrouds will not be able to reduce the temperature to proper level, thus possibly resulting in engine overheating.

Loose or Broken Belt A belt is often the driving link that turns the water pump at the correct speed for proper coolant flow through the cooling system. If a belt is loose or broken, it cannot maintain the proper speed, thus resulting in poor coolant flow and ultimately, engine overheating.

Faulty Water Pump Known as the ‘heart’ of the cooling system, the water pump is responsible for pressurising and propelling engine coolant through the cooling system. Any malfunction of the water pump, including eroded impeller vanes, seepage or wobble in the pump shaft, can prevent adequate coolant flow and result in engine overheating.

Leaky Head Gasket: A leaky head gasket can allow coolant to seep into the engine's cylinders or crankcase. Symptoms include a loss of coolant with no visible external leaks, and white steam in the exhaust, especially after restarting the engine when it has sit for awhile. A leaky head gasket can be diagnosed by pressure testing the cooling system, or by using a "block checker" that pulls air from the cooling system into a cylinder that contains a special blue coloured leak detection liquid. If there are any combustion gases in the coolant, the colour of the liquid inside the detector will change from blue to green. A leaky head gasket can often be temporarily sealed by adding a sealer product to the cooling system. But for bad leaks or ones that cannot be stopped with sealer, the head gasket has to be replaced.

Dragging brakes -- A disc brake caliper that is sticking or a parking brake that is not releasing may be making your engine work harder than normal to overcome the friction. Check the brakes and fix as needed.

POSSIBLE CONSEQUENCES OF ENGINE OVERHEATING

If your engine is overheating, it may start to detonate. The engine may rattle and ping and lose power. If detonation continues, it may damage the rings, pistons and/or rod bearings.

Overheating can also cause pisto scuffing. As the engine gets hotter and hotter, the pistons may swell to the point where there is no more room for expansion and they scrape against the cylinders, damaging the pistons and cylinders.

Exhaust valves may also stick or scuff in their guides. This can damage the valves, guides and
lead to a loss of compression.

Another consequence of engine overheating may be a blown head gasket. Heat makes aluminium swell almost three times faster than cast iron. Thermal stress can distort the head and make it swell in areas that are hottest like those between exhaust valves in adjoining cylinders, and areas that have restricted coolant flow like the narrow area that separates the cylinders. The typical aluminium head swells most in the middle, which can crush the head gasket if the head gets too hot. This will usually cause the head gasket to leak compression between adjacent cylinders, or leak coolant into the cylinders.

Engine overheating can also cause an overhead cam to seize and break.

Engine overheating may also stress old radiator and heater hoses and cause them to burst under the additional pressure. Steam that is generated inside the cooling system can also damage radiators with plastic end tanks.

WHAT TO DO WHEN YOUR CAR SUDDENLY START OVER HEATING.

At the first sign of overheating, shut off your air conditioner and open your windows: Doing so decreases the load on the engine and helps it cool off.

If you’re stopped in traffic and the temperature gauge is rising, shift into Neutral or Park and rev the engine a little: Doing so makes the water pump and the fan speed up, which draws more liquid and air through the radiator. The increased air and
liquid circulation helps cool things off.

Try not to ride your brakes: In stop-and-go traffic, crawl along slowly, on little more than an idle, rather than moving up and then
braking repeatedly. Brake drag increases the load on the engine and makes it heat up. If traffic is crawling, move up only when the gap between you and the vehicle in front of you gets too large.

If you think that your vehicle is about to boil over, drive to the right-hand side of the road, open the hood, and sit there until things cool off. Remember, don’t open the radiator cap under these circumstances, and if your engine has boiled over, don’t add water until the engine is quite cool again.

Use the heater to disperse engine heat. It may sound crazy, but it actually works. Flip the climate controls to vent, turn the heater all the way up, and turn the fan all the way up. If the
weather is hot, the inside of the car will heat up quite a lot. Point the vents out the windows as
much as possible to help reduce the temperature.
Why this works: The heater in your car uses engine heat to warm air in the cabin. Running your heater full blast takes a
significant amount of heat away from the engine, making it significantly cooler.

Www.everydaycarz.com

This reminds me of my escapade with my Nissan almera. My car temp Guage was already on the top I just parked and I was telling my buddy not to open the radiator cap but he said since there was no vapour and to enable the car cool down we should open the radiator cap.
Since I know what will happen, I just took three steps backwards and let him be stubborn. He used a cloth and started opening the cap. Wuuussshhh, hot boiling coolant all over his face and hands, I just laughed a little, the hausa guys around were just calling him "Dan kauye"