Driving with a broken AC would make you uncomfortable, but a damaged engine? Let’s hope you don’t find out.
But car engines are unpredictable and can flip your day over on its head when it comes knocking. Grinding, squealing and knocking are classic sounds associated with a troubled engine; but these are not the only things you should be wary of. For one, something as simple as a dead car battery can make you late for a meeting in the morning, but even that can be fixed if you know how to jump start a car.

It can be easy to overlook signs of potential engine trouble, or dismiss them as unimportant—but doing so could prove fatal, and your car’s performance is at risk. Fortunately, you can save yourself the hassle, headache, and money when you know what to look out for. 

These seven telltale signs would tell you when something is off under your bonnet.

Freaky noises
Be super conscious of knocking noises in your engine. Slapping, rattling, hissing or backfiring are common signs that show there’s a problem somewhere, and car problems are no good. It could be anything from a few screws loose to bad ignition wires, or a broken exhaust pipe, a carbon buildup, wrong fuel/too low octane levels, a bad spark plug or even a bad fan-belt. It could be more, it could be less, but it certainly is bad news.

Some of these may be easily fixed if spotted on time, and would generally cost you less money than it would if left unchecked. Just to be sure, and save yourself compounding trouble and expenses, seek out a mechanic or visit your local auto repair shop.

Excessive Smoking
Any kind of exhaust smoke is bad; not just for you, but for your car too. There are many reasons why your car exhaust may be smoking.

Black smoke could mean your engine has incomplete combustion, and as a result, burns too much fuel. A few things may cause this;

A clogged or damaged air filter
The sensors are out of order
Leaky fuel injectors
Mechanical damage in the engine

You should get the damaged parts replaced, and the engine fixed ASAP to cut down on all the smoke and fuel burning.

Grey/White smoke means a lot of things and is difficult to diagnose; but it could be a warning that either antifreeze (coolant) or water condensation has been mixed with your car’s fuel supply, it could also mean you’re having problems with a stuck PCV valve and excessive oil consumption.
Dark blue smoke simply means your engine is leaking oil into the engine’s combustion area and burns next to the fuel. Possible causes include. 
Damaged valve seals
Rusty or worn out engine components
Worn out piston rings.
A quick remedy will be to keep applying engine oil to the crankcase, - but you should consider taking the car in, to patch any rusty or damaged seals.

Check Engine Light Comes On
Check engine light is a dashboard warning light that is activated by the ECU  (electronic control unit) of your car. Some common reasons why you might be seeing the engine light check include:

Damaged or broken spark plugs
The fuel cap is not replaced or screwed on tight.
The Oxygen sensor has been damaged and needs to be replaced
The mass airflow sensor is damaged and needs to be replaced
Faulty or worn-out spark plugs
Other related electronic sensor issues

It is vital that you look for the source of any strange light on your dashboard array and fix it as soon as possible, as some faults can stop your car on the road. Of course, you can always troubleshoot why your car is not starting, but how long before your car completely packs up?

Because there are so many reasons your ECU may be giving you a check engine light, you should get your engine checked to avoid further issues.

To run, your car engine needs to remain at a certain temperature. If it gets too hot, the engine and its components could get damaged, rendering them unusable. To avoid situations like these, it is important to regularly test the cooling system of your car. 

Some of the reasons your car may be overheating are:
A bad thermostat
Leaks in your cooling system
Wrong coolant concentration
Burst hoses, and lots more.
If you are driving and you notice that the temperature gauge is starting to slide into the red or that the engine temperature light is switching on, pull over and switch off your car immediately to avoid engine damage.

Car Is Sucking Up More Fuel Than Usual
Higher fuel consumption may also be associated with a flaw in the way your engine processes fuel. When combined with noticeable engine light and other car engine-related symptoms, the problem could be more severe.

Once you notice that your car uses more fuel, check it out and have a professional look at it. This is going to save you money in the long run.

Strong Engine Smell in Your Car
If you can perceive a strong engine emission smell - exhaust, engine fumes or any other unusual odour in your car, then that’s a red flag for potential engine damage, and you need to get it checked ASAP.

Loss of Engine Power
Does your car feel different after you push the accelerator? Perhaps a slight stall, or an off-revving or rough sound? That’s a classic-tell-sign that something is inherently wrong with the internal workings of your engine. Do not ignore it, go get it checked and save yourself future headache and expenses. 

A Final Word
The engine is the soul of a car, and it is impossible to drive a car without one; much less a faulty engine. It may seem like nothing important on the first day; but do not ignore it on the second, or the day after that. Just like you would your body, routine car maintenance and check-up are necessary for its longevity. Prompt repairs would get it working better and have it back on the road faster.