14 September 2022
Dos, Don’ts and Whys of an overheating engine

Reserve overheating for flambé desserts, not your vehicle’s engine.

One of the last things that any driver wants is to be faced with an overheating engine. Putting aside inconvenience and loss-of-use, an overheating engine can quickly cause costs to spiral out of control if not attended to as quickly as possible. However, shtuff happens, so it’s good to be prepared and know what to do if and when faced with such a situation.

Do NOT do this… read on…

How to identify an overheating engine

One of the first things to be noticed is the coolant temperature gauge in the instrument cluster would be seen creeping toward the red zone. If said gauge is unavailable, a coolant warning light may illuminate on the dash instead.

DANGER ZONE!!!!!1!!11!!1ONE1!

This would likely be followed by an unmistakable sickly-sweet smell of coolant that permeates the interior of the vehicle. This could also be accompanied by steam billowing out from under the bonnet. Good-Samaritan motorists may also be urgently pointing at the car to indicate something has gone awry.

What to do

The first thing to do in the face of an overheating engine while on the road is to pull over, turn on the hazard lights and shut off the car as quickly as possible. This is because, if left unchecked, an overheat-situation can literally cause the engine to melt and distort, and this would mean breaking one’s wallet to shell out for a new engine.

Pull over, turn on hazard lights and shut off engine as soon as possible

That’s the best-case scenario.

The worst-case scenario involves one’s vehicle being engulfed in flames while the owner sadly watches their car literally burn to the ground. ‘Nuff said.

Don’t be THIS guy

Next, get behind the crash barrier, if any, or onto the sidewalk and stand away from the vehicle’s engine. Most passenger cars are front-engined, so this would mean standing past the rear of the car. In the event that something decides to erupt or explode, one is at least not directly in the line of fire, and the closed bonnet would keep help things contained.

Finally, whether or not one is car-savvy, the best thing to do at this point would be to contact an automotive concierge service like AutoApp to arrange to have the vehicle towed to a partner-workshop for further diagnosis and repair.

What NOT to do

Never EVER open the bonnet when an engine is already overheating. Should the radiator cap, coolant-overflow tank, plastic radiator end-caps or coolant hoses fail while the bonnet is open, extremely hot, scalding coolant and steam can shoot out like a geyser and seriously injure anyone in its path.

Scalding hot coolant and steam erupts like a geyser

Remember, the cooling system is pressurised and coolant usually sits around 75°-105° Celsius, and higher in an overheating scenario. If hospital-stays and skin grafts are not on one’s itinerary, leave the bonnet firmly closed and await the tow truck.

There’s a good reason for this warning on radiator caps

Do not ignore the coolant temperature gauge and keep driving when the engine is overheating. This will most likely lead to the aforementioned melted-engine at best and a flame-engulfed vehicle at worst leaving its occupants charred beyond recognitio ’nuff said.

There is ONE scenario where driving MAY be continued, but with a proviso that this applies ONLY to car-savvy folks who know what they’re doing.

If coolant temperature remains relatively normal during driving, and only starts to rise when the vehicle is stationary, then turn off the aircon compressor via the A/C button, wind down the windows, set the aircon thermostat to full heat and set the blower to maximum fan speed. This will allow for some additional cooling through the vehicle’s heater core within the interior, and help to mitigate rising coolant temperature somewhat. The engine would likely need to be turned off and restarted at traffic lights though, but it MAY be possible to limp the vehicle to the workshop in this manner. Again, the best thing to do would be to shut the engine off and get the vehicle towed.

Press ‘AC’ button to turn off aircon compressor, then set temperature to full heat and blower to maximum fan speed for additional cooling through the heater core

Why do engines overheat?

The most common source of overheating engines comes from blocked coolant passages. If the engine’s cooling system is not properly maintained with coolant changes at mandated intervals, gunk can build up on the inner walls of the engine’s coolant jacket, resulting in poorer heat exchange from the engine to the coolant. If left unchecked, this in turn can lead to the rest of the cooling system gunking up, further worsening heat-exchange with the ambient air.

Gunk in coolant… ewwww….

A good example of a neglected cooling system can be seen on this ChrisFix video. The point is to never allow the coolant and cooling system to degrade to such a state. Automotive concierge services such as AutoApp can take the headache and worry out of the equation, advising car owners when it is time to do a coolant flush, with pictures to illustrate why.

Another source of overheating engines is low coolant levels. There are a number of reasons why coolant levels can run low. Here are two common ones.

Always ensure coolant level is topped off at the overflow tank, not at the radiator

The first is a faulty head gasket, which allows coolant to enter the engine’s combustion chamber and be burned away during the combustion process. This phenomenon is most apparent during first-start in the morning when the engine is cold. A noticeable and relatively large puff of white smoke will be emitted via the exhaust pipe when the engine is started, indicating coolant in the combustion chamber(s). The effect of burning coolant off causes air pockets to be introduced into the cooling system, thereby degrading its performance. Also, hot combustion gases can make their way past the faulty head gasket and into the cooling system, thereby over-pressurising the system and further degrading cooling performance.

Faulty head gasket can cause coolant loss

An unnoticed crack or puncture somewhere within the cooling system can also cause a leak, thereby running coolant levels low and degrading cooling performance.

Puncture in radiator leaks coolant

Said crack can be easy to track down if it is in the radiator, one of the radiator hoses, or in the radiator’s plastic end-caps. Many a Subaru owner would be familiar with the latter, yours truly included. Leaks caused by such cracks are fairly common due to wear and tear, and keeping on top of things is key to a worry-free motoring experience. AutoApp can help owners stay ahead of the game in this regard, where checks are done on the engine and running gear during servicing, with preventative maintenance issues caught and highlighted before they occur – a mere oil change is simply not enough.

Radiator hoses are wear items. Quick fixes are NOT the way to go. Replace when needed.

However, if the crack is located within the engine block or head, then it can be much more difficult to locate, and would require much more involved professional diagnosis. The usual cause of such cracking is one or more previous episodes of engine overheating where things were not properly handled in a timely manner. However, there have been instances of manufacturing defects that have also led to such occurrences.

A faulty thermostat can also lead an engine to overheat. The thermostat is supposed to open at a predetermined coolant temperature and divert hot coolant to the radiator to be cooled. However, if the thermostat is stuck closed, then hot coolant from the engine cannot make its way to the radiator, resulting in the engine overheating.

When a thermostat fails in the closed position, an overheated engine is mere minutes away

Finally, a fault in the cooling fans can also cause engine overheating. This may present itself in terms of a blown fuse, faulty fan relays, faulty fans or a combination of the three. This specific issue causes coolant temperature to rise while the vehicle is sitting stationary with the engine running at traffic lights or in a jam, and may not be apparent while underway because sufficient air is blowing past the radiator to keep things cooled. The aforementioned interior heater workaround combined with stopping and starting the engine would come into play in this scenario to limp the vehicle to a workshop, but best to shut down the vehicle and have it towed.

Failed cooling fans can wreak havoc, especially in slow-moving to standstill traffic

Keeping cool

No one wants to be caught out with a sizzling engine. However, as mentioned before, shtuff happens, so it is good to know what to do when the situation calls for it. Having AutoApp handy for such situations can mean the difference between being caught out like a deer in headlights, and catching and addressing the issue in a timely and proper manner. Less headache means more win for everyone involved.

Read more car maintenance tips and tricks here.