CONTROL IS THE BEST PREVENTION
Blood pressure is said to be a silent killer that can do great harm to the body. The same is true for cars, so anything to do with pressures must always be kept under control.
Pressures in the car are necessary for the operation of many systems. They are crucial for safety, comfort and also for the car's start-up, so this is actually an interesting chapter. Find out what each pressure means and how they affect your driving – can you monitor them to prevent potential breakdowns?
Oil pressure is crucial for the engine to work properly. Oil is constantly circulating in all parts of the engine, so there is an oil film between all the metal parts that rotate or slide on top of each other, ensuring operation with minimum friction and overheating. The slightest lack of oil in the sliding bearings of the crankshaft or camshaft can severely damage or even completely destroy the engine in seconds. Similarly, the lack of oil film on the cylinders, on which the pistons slide with their rings, causes high friction, overheating of parts and destruction of the engine, whether diesel or petrol versions. To ensure the oil pressure is sufficient and the oil from the lowest point of the engine – the sump or crankcase – reaches all parts, the oil pump is needed to provide the necessary pressure. The oil circuit is equipped with pressure sensors that react to a drop in pressure and immediately illuminate a red light on the dashboard. If the pressure drops below the permissible limit and the oil light turns on, the vehicle must be stopped immediately! In engines where drivers do not check the oil level (which is definitely a bad thing), the oil can run out as the engine more or less uses it up. Newer vehicles also have oil quality sensors that detect impurities and moisture in the oil and warn when it's time to change it.
Brake pressure
In a hydraulic braking system, pressure is the basis of its operation. Applying pressure to the brake pedal creates pressure in the brake master cylinder (pump), which transfers this pressure to the cylinders in the wheels (brake shoes or drums), which in turn apply pressure to the brake pads or linings on the discs or drums. The ABS also works in this circle and can reduce or increase this pressure as needed, redistributing it to the individual wheels to a greater or lesser extent to prevent their blocking. Of course, the prerequisites are that the system is leak-proof and that the brake fluid is at the correct level, which can be read on the reservoir itself. A slight decrease in oil level over time is normal as the brake pistons in the cylinders move longer due to wear of the brake pads or linings. Any significant drop in brake fluid level should be checked by a technician, as this can be a sign of a leaking brake system, which is extremely dangerous. If the brake fluid darkens, it is due to ageing and needs to be replaced. It is recommended to change the brake fluid every two years because it is hygroscopic (absorbs moisture), which lowers its boiling point.
Pressure in the air conditioning system
The coolant pressure in the air conditioning does not affect the driveability and performance of the vehicle, but if lost, the ride quality is significantly reduced. For the air conditioning to work properly, it is essential that the system contains enough R 134a refrigerant gas or the new, more environmentally friendly R 1234yf. At rest, the pressure in the air conditioning is typically around 5–6 bar (depending on the size of the system), but can reach 15 bar in the high-pressure section of the system when the compressor is running. This is a very high pressure, which requires the system to be sealed perfectly. Unfortunately, we can't do anything ourselves without a specialised controlling and charging system and a professional workshop. Every air conditioning has a sensor that automatically switches off the compressor when the pressure is too low or even too high, and passengers will notice that the air conditioning is no longer cooling. There is no warning light for such a fault, and the low pressure information can be read using the diagnostic tool in the workshop. Air conditionings need regular maintenance. However, topping up the air conditioning occasionally or seasonally is not the right solution – a drop in pressure means the system is leaking somewhere, which can ultimately damage the compressor and the whole system. If everything is OK, the pressure is stable and refilling and servicing with a suitable device is only necessary after a few years. The device extracts all the gas, weighs it, vacuums, cleans and de-moisturises the system, and then returns a prescribed amount of purified gas to the system.
Tyre pressure
Tyre pressure is extremely important for the safety and driveability of a car, but it is often neglected. It may be hard to see, but the whole vehicle has a surface area of four palms on the road surface. If the tyre pressure is not adequate, this surface is deformed and the contact between the tyre and the ground is not optimal. As well as making it harder to stay on course, the vehicle's handling characteristics change, especially when driving in the rain, making it harder to displace water. It is therefore very important to check the pressure with a calibrated pressure gauge at least once a month and adjust it to the factory-specified value. If the pressure in one or more tyres is dropping rapidly, it is best to visit a vulcaniser. He will check whether there is damage to the tyre or whether the valves only need to be replaced. Vehicles with a newer production date (as of 2015) have a pressure monitoring system that alerts the driver when a tyre is leaking, making it much easier to control. Tyre pressure should always be set according to the vehicle manufacturer's recommendations, making sure to adjust it to the load (higher pressure with higher load).
Pressure in the cooling system
Pressure in the cooling system causes the coolant to heat up and expand due to the engine heat it absorbs. For a long time, cooling systems have been using a coolant suitable for year-round use, rather than water. Besides cooling, the coolant also provides corrosion protection, while its boiling point is higher than that of water. If the pressure is too high, a valve, usually located on the filling plug itself, reduces the pressure and releases the excess liquid. This happens when there is something wrong with the cooling system and the coolant is not cooling sufficiently. When the coolant overheating warning light turns on, you should take this warning seriously and stop the vehicle immediately. The liquid level depends on pressure and temperature and is monitored at the expansion vessel. The vessel is usually made of white or clear plastic with clearly visible minimum and maximum markings. The level fluctuation between the two marks is normal and also depends on the engine temperature. Check the fluid level when the engine is cold. If you notice that the engine is losing coolant, visit a workshop immediately to avoid major damage.
Compression pressure
To put it simply, compression pressure gives power and life to an engine. Without it, there is no necessary explosion of the gas mixture in the cylinder, which is a prerequisite for pushing the pistons hard and providing the necessary mechanical force to turn the crankshaft. The most favourable air–fuel mixture is 14.7:1, which means that in such heated air only little fuel is needed to produce an explosive mixture. The air warms up it these pressures to several hundred degrees Celsius. Cylinder pressure rises to several tens of bar in diesel. But we have come to express compression in terms of the so-called compression ratio. For petrol engines around 12:1, while for diesel engines the ratios are higher, e.g. 30:1. This is how we denote the ratio of the largest and smallest volume in the cylinder – the cylinder volume when the piston is at bottom or top dead end. The higher the ratio, the higher the pressure in the cylinder. As the piston rings that seal the space between the piston and the cylinder wall age and wear, micro-leakages form and, as the piston rings become less tight, the pressure drops accordingly. An engine with low compression will gradually lose power and liveliness, and the exhaust gases will generally contain more smoke. Compression pressure is tested in the workshop using analogue or digital pressure gauges. When the engine is turned to "cold" with an electric starter and without ignition of the mixture, these read the pressure reached by each cylinder. A slight drop in compression pressure over time and after high mileage is normal. It is more important that the pressure is even so that one cylinder does not lag behind the others. Proper engine maintenance, regular oil changes and quality fuel, together with the maintenance of the exhaust gas cleaning system (AGR, DPF, etc.) are the only ways to ensure "high" compression of our engine for a longer time.
This article was published in Bartog INFO No. 3, Summer 2022. Read the magazine HERE.