The Engine and Transmission: How They Work and Common MalfunctionsUpdated Jan. 2, 2021
The energy used to propel your vehicle along the roadway is created in the engine. Most vehicles have internal combustion engines (ICE) which produce power by exploding fuel in combustion chambers or cylinders. How much power a vehicle can produce depends on how many cylinders the engine has. More cylinders equal more power.
There are many different combustion engine configurations on the market today, though they all rely on similar principles. Most modern vehicles have 4-cylinder, 6-cylinder or 8-cylinder (V8) engines. A piston connects each cylinder to the engine’s crankshaft, which converts the thermal energy produced in the cylinder to kinetic, rotational energy, or torque. This energy is then transmitted to the wheels via the transmission and driveshaft. Let’s take a closer look at how these components work and what the driver can do to maintain them.
The four-stroke cycle
Power is produced in an engine cylinder through what is known as the four-stroke cycle. The piston in each cylinder moves up and down while the engine is running; each upward or downward motion is called a “stroke”. Below the cylinder, the piston is connected to the crankshaft. Every two piston strokes move the crankshaft one complete 360-degree rotation.
Here is how the four-stroke combustion cycle works:
The piston moves down while the fuel intake port is open, and the exhaust port is shut. This creates suction which draws fuel and air into the cylinder.
The piston moves up while both the fuel intake and exhaust ports are shut. This compresses the fuel-air mixture in the cylinder. When the piston reaches the top of the cylinder, the compressed fuel is ignited by a spark from the spark plug.
The piston moves down, powered by the force of the explosion. This keeps the crankshaft rotating. Both the exhaust and fuel ports are still closed.
The piston moves up, as the exhaust port opens. This pushes out the waste gases that were produced during the explosion. Then, the entire four-stroke cycle begins again.
As every cylinder firing (creating explosions) simultaneously would damage the crankshaft and the combustion chambers themselves, each cylinder’s piston is built to fire according to a set firing order. In a four-cylinder engine, the firing order might be something like 1-3-4-2, or 1-2-4-3.
You can see how fast the crankshaft in your engine is rotating by looking at the tachometer on the instrument panel. Most modern gasoline-powered engines perform well when the crankshaft is spinning at 5,000 to 6,000 revolutions per minute. This equates to about 100 revolutions every second and 3,000 explosions in each cylinder, every minute!
The four-stroke cycle relies on the opening and closing of the fuel and exhaust valves in each cylinder being perfectly timed. The timing belt which connects the crankshaft to the camshaft coordinates this operation. If something goes wrong with the timing belt while the car is running, the engine may be irreparably damaged.
Timing belts are built to be hard-wearing, using high-quality rubber and reinforced with nylon cords. Unfortunately, timing belts are subject to incredible forces inside the engine and will eventually wear out. Usually, a vehicle will need a new timing belt every 60,000 miles or so. You can find the manufacturer’s recommended timing belt replacement frequency in your vehicle owner’s manual.
Quite often, timing belts break with very little warning. For this reason, it is important to get your engine checked out by a mechanic when you’re getting close to the 60,000-mile mark. If you notice any of the symptoms listed below, get it looked at right away. These problems may indicate that the timing belt is starting to wear out or is damaged:
- A “ticking” sound coming from the engine. This can also indicate low oil pressure.
- Turning the key in the ignition activates the starter motor but the engine will not turn over. This indicates a broken timing belt.
- Oil leaking from the front of the engine. If the oil is coming from the timing belt, it may indicate that the cover is loose.
The transmission mediates the transference of power from the engine to the wheels. This is necessary even though the engine’s power has already been converted to torque (rotational force) when it reaches the crankshaft, as the crankshaft rotates too rapidly to directly rotate the wheels.
Using a series of gears, the transmission adjusts how much power makes it from the engine to the driveshaft, which is attached to the wheels. By moving up through gears as the vehicle accelerates (either automatically or with input from the driver) the transmission allows for precise control over wheel-speed while maximizing engine performance. The difference in speed between the wheels and the engine is greater in lower gears and less in higher gears. This is not something you need to worry about this too much if you drive an automatic vehicle, as the torque converter between the engine and the transmission will select an appropriate gear for you. In a manual, the driver must move up and down through gears using a stick shift next to the driver’s seat.
Both automatic and manual transmissions use transmission fluid to keep their moving parts lubricated and interacting smoothly. It is important to check your transmission fluid levels regularly – particularly as your car gets older – as a leak could result in insufficient lubrication and serious damage.
Common transmission malfunctions
Low transmission fluid is one of the most common causes of transmission problems. There may be insufficient fluid in your vehicle’s transmission if:
- The transmission is “slipping”.
When you attempt to change gears, the transmission slips out of the new gear and returns to the previous gear. Transmission slipping may also be accompanied by grinding noises and in automatic vehicles, abrupt up or down gear shifts that feel jerky.
- The transmission overheats.
This may cause loss of power, a smell of burning or smoke emanating from underneath the car.
- Irregular gear shifts.
If gear changes become sudden, delayed or not as smooth as usual, your transmission fluid may be low.
- Failure to shift gears.
If the transmission will not shift gears at all, it is likely that your fluid reservoir is either completely empty or on its way there.
If transmission fluid levels remain too low, for too long, the transmission may eventually fail altogether and need to be replaced. Transmission reservoir leaks are the number one cause behind insufficient fluid in the transmission. However, this can also be a result of a solenoid malfunction. The solenoid manages the flow of fluid through the transmission, so if you cannot find a leak, this component may be the culprit.
In automatic vehicles, unusual sounds and grinding noises coming from the transmission may be caused by worn bearings in the torque converter. If you cannot identify any other cause for your transmission problems, you may want to ask a mechanic to check this out.
One of the best things you can do to look after your engine and prolong your vehicle’s life is keeping the motor oil topped up. The engine is powered by gas but needs oil to stay lubricated and run smoothly. Without this lubrication, the crankshaft, pistons, camshafts and other moving parts in the engine would create enough friction to wear away and destroy each other. Motor oil also serves to cool and clean moving parts, maximizing the engine’s performance.
The motor oil in your engine is designed to be recycled, so you should not have to top it up too often. Though engine oil will eventually degrade and become less effective, so it does need to be replaced intermittently. Check your car owner’s manual for information on oil changes, as it will tell you how regularly you need to check and replace the motor oil. Unless you are certain you know what you are doing, it is best to leave complete oil changes to a qualified mechanic.
The moving parts and exploding fuel in combustion engines produce an enormous amount of heat – more heat than can be converted into kinetic power. If left to its own devices, the engine in your vehicle would become so hot that key components would start to fail. The engine’s coolant system is designed to prevent this, by circulating coolant fluid around the engine compartment in a network of tubes.
Engine coolant has an extremely high-boiling point, which allows it to absorb heat from the engine safely. From its storage tank in the radiator of your car, coolant travels around the engine and absorbs the heat it produces, allowing the engine itself to remain cooler. When the heated coolant fluid returns to the radiator, its temperature is lowered by the radiator fans and air passing through the front of the engine compartment as the vehicle moves. The radiator also has a pressure valve that releases excess coolant into an overflow tank, as the liquid expands as it gets hotter.
This entire process is managed by a thermostat, which detects the temperature of the engine and the coolant fluid. The thermostat allows the engine to heat up to the temperature required for it to function correctly, then maintains that temperature by releasing coolant into the system. When the coolant fluid becomes too hot, the thermostat ensures it is returned to the radiator to be cooled.
The instrument panel on the dashboard features a warning light that will activate if the engine becomes too hot. This can happen during extremely hot weather, or if coolant levels are too low. If you drive an older vehicle, you may also have a temperature gauge on the instrument panel which draws information from the engine thermostat. If this temperature gauge shows that the engine is regularly too hot, or if the engine temperature warning light remains active, you may have a problem with your coolant system.
It is essential to get this checked out by a mechanic immediately and stop driving the vehicle in the meantime. If your engine overheats, all its component parts are at risk of breaking down.
Common engine malfunctions
Nothing throws a driver into a panic quite like the realization that something is wrong with their engine. Fortunately, many common engine malfunctions have easy and inexpensive solutions. Keep in mind that serious engine malfunctions usually start out as minor issues. If you monitor the health of your engine and get small problems checked out right away, you should be able to avoid dangerous situations and expensive repairs. Below, you will find descriptions of some common engine malfunctions and their potential causes.
The engine is overheating
Your engine temperature gauge is well into the red, steaming vapor is billowing from the engine compartment and a nasty smell is coming through your air vents; it’s safe to say, the engine is overheating. As mentioned earlier, this is usually the result of low coolant levels. Though, an overheating engine may also be caused by:
- A broken thermostat
- A broken cooling fan in the radiator
- A blockage in the air filter
- Damaged radiator hoses
- A broken or incorrectly fitted radiator cap
These are all issues that will need to be rectified by a mechanic, though fortunately, they tend to be relatively simple and inexpensive jobs. If your coolant levels appear to be fine, it is best to get your vehicle to a mechanic at the next opportunity. First things first however, you need to pull over to a safe spot and let the engine cool down.
You can help your engine cool down by switching off the air-con and cranking up the heating, as this will direct heat away from the engine and into the passenger compartment. Never mess with the radiator or anything else in the engine compartment while the engine is still hot.
The engine will not start
Understandably, this is one of the most frustrating and worrying engine malfunctions. If your car will not start, it is easy to assume that something terrible (and potentially expensive) has happened to the engine. Thankfully, this is not always the case. An engine that will not start could be caused by:
- A faulty battery or corroded battery terminals
- A failed fuelled pump
- Dirty fuel injectors
- A faulty starter-motor
- A faulty alternator (which is responsible for recharging the battery)
- A broken or malfunctioning ignition switch
If you have reason to believe that the malfunction may be caused by a dead battery (for instance, if you left your headlights on by mistake), you may be able to jump-start the engine using jumper cables and another vehicle’s battery. Otherwise, the issue will need to be investigated by a mechanic.
The engine is making a strange noise
A strange noise coming from your vehicle’s engine could indicate any number of problems, but it definitely suggests that something is amiss. If you hear odd noises in your car, make a point of noting what kind of noise it is. This information may help a mechanic know what to look for when diagnosing the issue. Do you hear rattling, squealing, ticking – or something else?
A rattling sound coming from the engine compartment often indicates a serious problem. If the engine oil warning light comes on while you hear the rattling sound, it may be that the moving parts in your engine are dangerously under-lubricated as a result of low oil levels. Rattling sounds may also be caused by poor belt tension, a problem with the air conditioning compressor or less seriously, a loose reservoir cap.
Squealing or screeching.
A squealing or screeching sound usually means a problem with one of the engine’s belts. The sound may be an indication that the belt is slipping, damaged or corroded. If the high-pitched sound is accompanied by a sudden rise in engine temperature, it may be that the water pump has failed and will need to be replaced. Make sure you get the engine checked out immediately. If you’re lucky, it could just be that one of the belts needs tightening.
Clicking or ticking.
A clicking or ticking sound may mean that the valve train (connecting the camshaft to the cylinder valves) has shifted slightly out of place and needs to be adjusted. Moderately low motor oil can also cause clicking or ticking sounds anywhere within the engine, so this is the first thing you should check.
A whining noise may be the result of wear to your transmission, so you will need to get the engine checked over by a mechanic right away. Problems with the power steering system can also cause whining sounds. It may be that your power steering fluid is running low, which is relatively easy and inexpensive to sort out.
Keeping your engine healthy
If your vehicle is relatively new, you are unlikely to experience any serious issues with the engine. However, even new engines can malfunction when they are not cared for correctly. All the information you need to keep your engine in great condition can be found in your vehicle owner’s manual. Take the time to read through it and try to develop good vehicle-maintenance habits! The extra time and effort spent now will save you a great deal of time, money and hassle later.
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