Diesel engine speed is one of the most common questions for diesel car owners. There is only one answer - it all depends on the parameter of the power unit, its power and torque, which together determine the maximum speed limit for diesel engines. In order to open this topic widely, we will give some information about the features of diesel engines and their speed.

The first reason for low revs in diesel engines is the increased mass of the piston and connecting rod compared to gasoline ones. Further, these are the features of the ignition of diesel fuel. Incomplete combustion of the diesel mixture does not allow the engine to develop high speeds.

The mixture simply does not have time to burn out in the cylinders and the power unit does not have time to complete its full duty cycle. For this reason, at exorbitant speeds, the working cycle is disrupted and the specific power of the diesel engine per liter of volume decreases.

By the way, it is because of this that special diesel fuel is produced for sports diesel cars, which has the ability to quickly ignite and burn out completely.

The next factor that reduces the ability to revolutionize a diesel engine is the so-called compression ratio, which occurs at exorbitant revolutions. Compression requires extra effort and starts stealing some of the engine's power, some of the engine's energy simply starts to go into spinning itself. Both of the above factors increase with increasing rpm, as a result of which the ability to peak in diesels is usually limited.

For these reasons, it is not recommended to accelerate the diesel to the maximum, since after overcoming the so-called torque revolutions, the thrust will not increase further. The desire to increase the speed can only lead to wear of the cylinder-piston group and to excessive consumption of fuel and engine oil.

Power simply decreases after 3800-4000 rpm. For the reasons described above, owners of diesel cars need to reasonably adjust their driving style.

Turbodiesel units with which heavy KAMAZ vehicles are supplied have a speed limit of -1800 rpm. As for diesel small cars used in cars, they have a maximum reserve somewhere in the range of 2200-2500 rpm.

Here is a small table (let's imagine that we are dealing with a 6-speed transmission):

• 3rd gear - from 30 km/h to 50
• 4th gear - from 50 km/h to 70
• 5th gear - from 70 km/h to 100
• 6th gear - from 100 km/h

Note that in 6th gear at a speed of 100 km / h, the revolutions become 2000 rpm, beyond which the increase does not make sense, since diesels have an optimal torque in the range of 1500-1900.

The general strategy is that if the engine is running smoothly, then you can slow down a little. Gearshift scheme: first gear - all revolutions, starting from second - 1500 rpm. after third gear - 1700 rpm, and in fifth - 1900. If you violate the rules for shifting, you expose the power unit to excessive shaking and vibration, and at low speeds, the oil does not lubricate the far gears enough.

According to the above facts, it follows that the diesel engine does not need to increase speed to achieve high torque. It is this feature of diesel engines that makes them indispensable for use in freight transport, for which high speed is not essential.

For comparison, gasoline engines can be cited as an example. They are much more powerful than diesel ones, they need high power at maximum speeds to achieve high speeds. The gasoline engine does not increase power immediately, reaching a peak at increasing speeds. With a diesel engine, things are different, they gain maximum power much earlier, but already at medium speeds, the thrust of the diesel engine weakens.

Idling speed of diesel engines can give different values, which depend on the viscosity of the oil or the load on the generator. High RPMs are best measured at idle with full throttle. According to the instructions, they can be 4900-5000.

Many drivers, for the sake of experimentation, try to adjust the cable on the automatic transmission, which is better left untouched without urgent need, as the transmission system can be upset. When experimenting with idle speeds, it should be remembered that reduced speeds have a negative effect on the diesel engine as a whole, especially on the turbine.

Let's continue the topic of idle diesel engines. There is a belief that a diesel engine does not like starts, so it is better not to turn it off often. If you follow this advice, there is a risk of damage to the rings, they simply begin to wear out. This happens from the abuse of idling at speeds below 2000. This often happens in the north, where drivers of heavy diesel cars do not turn off their engines for days.

There are basically two problems with this. The first is coking injectors. The problem is solved by loading at operating speed, which cleans the nozzles. The second problem, which is related to the coking of the rings, is also solved. It is necessary to increase the speed while maintaining oil pressure, and in case of frost, cover the radiator with cardboard.

In general, with good oil pressure and uninterrupted operation of the cooling system, a diesel engine is able to withstand idling for a long time, but we must not forget about good regassing with an increase in speed, as mentioned above.

But you can’t overdo it, you, of course, will eliminate deposits by increasing the speed, but the rings will still gradually wear out, as the oil pressure drops at idle. Hypothetically, if the oil pressure did not fall, the diesel engine could work forever devouring all the available diesel fuel.

If heavy-duty diesel engines can hardly withstand a decrease in load of 20 percent below the calculated one for a long time, then for light automotive diesel units the norm is completely different.

For diesel cars, the consequence of prolonged work on idling not as catastrophic as for trucks. For passenger diesel vehicles, there is a different risk. The maximum allowable speed can lead to self-ignition in the form of detonation, which is fraught with the destruction of the piston group.

In the process of modernization, diesel units in terms of speed are increasingly approaching gasoline ones. however, they will always be inferior to gasoline ones. A powerful diesel can be accelerated up to a maximum of 4500-4800 thousand rpm, and 7 thousand rpm for gasoline units from sedans is something common.

Manufacturers of diesel units are constantly improving the characteristics of engines. Power increases, torque improves, ways to save diesel fuel are improved. Note the modernization of the fuel supply system to the cylinders. This is the so-called preliminary fuel injection, it reduces the impact moment and improves the combustion of the fuel-air mixture. All of these innovations combine to help the diesel run less harshly.

We can also note the refinement of the gas distribution mechanism, leading to an increase in the number of valves. Yet, the real revolution was the addition of a turbine to the diesel engine. These small deviations from the main theme were intended to remind car owners that diesel units evolve year after year. RPM characteristics are constantly improved, gradually equalizing power to torque.

A separate word deserves the Japanese contribution to diesel technology. The owners of jeeps on diesel units of the latest models drew attention to the presence of the “Turn on the warm-up mode” button. According to the instructions, the button should be activated during winter frosts. Its function is that it raises the idle speed to 1300-1400.

The revs are kept only in idle mode, if you add gas by engaging the clutch, the revs will automatically take on the standard value of 800-900. In other words, the Japanese design offers an increase in idle speed solely to warm up the engine.

After starting, a cold diesel or gasoline engine may vibrate slightly at idle, especially in winter. The diesel engine is more prone to vibrations initially due to a number of features. Idling (idle speed) is the operation of the engine when the clutch is disengaged and the gearbox is in the "neutral" position. In other words, no torque is transferred from the engine to the wheels of the car.

The idle speed for most diesel engines is around 680-780 rpm. Gasoline units may have a higher rate. Vibration at idle is noticeably felt on the steering wheel of a fully serviceable engine, especially when the car is warming up. After leaving for operating temperature the engine should start running absolutely smoothly. Also, the vibration should significantly decrease or completely disappear with an increase in speed, both on a cold and warm engine.

Causes of diesel vibrations

If this does not happen, then the vibration of the diesel engine at idle can be caused by a number of reasons, among which the most common are:

• malfunction or in one cylinder;
• large in cylinders;
• damage to the engine mounts;
• malfunction or diesel injectors;
• errors when setting timing marks;
• incorrectly set injection advance angle;

In some cases, the diesel engine vibrates intensively at idle without any signs of malfunction, allowing the car to operate normally under load. With more serious problems, the diesel engine frankly and smokes, does not develop power under load, and the consumption of diesel fuel and engine oil increases.

Diesel engine mounts

This malfunction should be determined by analyzing the intensity of vibrations at idle before and after warming up, as well as during the operation of the diesel engine under load. Often, the diesel shakes due to the fault of the pillows, regardless of temperature. Vibrations appear not only at idle, but noticeably decrease in the medium speed mode.

Diagnose the problem as follows. The hood is opened, the driver starts off on the car, moving forward, then repeats a similar movement back. This is necessary for the buildup of the internal combustion engine on the pillows. At this time, the assistant stands nearby and evaluates the displacement of the motor. It is necessary to identify possible deviations when swinging on the pillows forward and backward.

If the motor moves noticeably forward, but shifts less back and vice versa, and also sharply sinks when jerking to one side or the other instead of a smooth return motion, then the engine mounts need to be replaced. It should be noted that the outwardly serviceable appearance of the pillow cannot be guaranteed to indicate the absence of malfunctions of this element.

Stopping one of the cylinders

In this case, the diesel engine idling vibrates much more strongly (troit). There can be many reasons, ranging from diesel injector coking or failure of a glow plug to burnout or. The problem of a non-working cylinder can go away after warming up the diesel engine, and manifest itself in the process of further driving. For a more accurate determination, it is necessary to check the presence of fuel supply to the cylinder, and also check the compression by measuring the pressure inside the cylinder.

Analysis of compression indicators

During operation, the motor wears out unevenly. Different compression in the cylinders of a diesel engine can cause vibrations at idle. All cylinders are working at the same time, but the ignition of the mixture can occur both ahead of time and with a delay. This leads to an imbalance, especially noticeable at idle during warm-up.

After the engine reaches operating temperature and under load, vibrations decrease or disappear, since an increase in thermal clearances with heating of the internal combustion engine increases compression in the cylinders. To determine the malfunction, it is necessary to measure the compression in each cylinder and compare the indicators with acceptable standards.

injection pump and diesel injectors

In idle mode, the injection pump is responsible for supplying fuel and maintaining idle speed. Insufficient amount or overfilling of diesel fuel will lead to vibrations at idle. Often, after warming up the engine, increased vibrations disappear. If the motor shakes strongly or the shaking does not go away at operating temperatures, then the pump needs to be adjusted.

Many constructively have special adjusting screws. These screws determine the amount of diesel fuel supplied to maintain the idle speed of a particular engine specified by the ICE manufacturer. It should be noted that it is not recommended to independently regulate the speed without proper experience.

Progress has not stood still for a long time: the former low-speed, but noisy diesel engines began to work quieter, and their power, and, accordingly, their dynamics increased. Moreover, a noticeable breakthrough in this direction happened when turbocharging began to be installed on diesel power plants. Today, many cars equipped with diesel engines have a turbine in their design. However, not all owners of cars with such units know how to properly operate a turbodiesel engine so that it lasts as long as possible. We have prepared eight simple tips that will help current or potential owners of machines with similar units to avoid miscalculations in the operation of the turbine.

Council number 1. Keep the oil level under control.

All engines in general, and the turbocharged diesel engine we are considering in particular, are not recommended for oil starvation. After all, the oil in such a unit plays special role, lubricating the plain and rolling bearings of the turbocharger. When the engine oil level drops, the bearings do not receive the right amount of lubrication, which leads to their rapid wear and failure. Therefore, we recommend that you check the oil level in the crankcase as often as possible and, if a deficiency of lubrication is detected, you need to immediately top up the amount. In addition, it is necessary to find out the reason why the oil level in the system drops (this may be contamination or leakage of the oil system, failure of the oil pump, etc.) and eliminate it immediately.

Council number 2. Use only high quality motor oil.

Once you have purchased a car with a turbodiesel engine, do not skimp on refueling it with high-quality and manufacturer-recommended engine oil. Here, as in the well-known saying: save on fish, get a bad yushka. Above, we have already indicated what role engine oil plays for a turbine, so pouring any kind of oil into the engine means dooming the turbocharger of the power plant of your car to a slow death in advance. It is important to remember: oils recommended for turbocharged units are different in composition from conventional oils due to the fact that when working in a turbine they are exposed to where high temperatures and loads than in a naturally aspirated engine. Another important aspect: it is highly not recommended to mix oils of different viscosity, for example, add 5w-30 oil to the engine if 10w-40 has already been filled there. Therefore, we advise: fill in oil of the same viscosity coefficient and preferably of the same brand.

Council number 3. Monitor the quality of diesel fuel.

A diesel engine turbine is sensitive not only to the quality of the engine oil, but also to the quality of the fuel you feed your car with. When using low quality fuel, clogging of the engine fuel system is likely, which, in turn, affects the loss of engine power, due to which the turbine is forced to work at its power limit in order to fill this gap in speed. And this can lead to a reduction in its service life. Therefore, we recommend, if possible, to refuel only at proven gas stations. If you are not sure about the quality of the fuel, it is better to filter it further.

Council number 4. Avoid overgassing when starting a turbocharged engine.

This advice should be followed, first of all, by those owners of cars who do not have a Start & Stop engine start / stop system installed. The fact is that when starting the engine, the oil channels are not yet filled with engine oil, when you press the accelerator pedal, you give a load to the turbine, which rotates almost without oil, as a result of which its components (bronze-graphite sliding and rolling bearings) wear out quickly, which eventually leads to failure of the turbocharger. Therefore, we strongly recommend that you apply gas smoothly, and for some time (within 5 minutes maximum) after starting, let the engine idle, and then start moving at low speeds, gradually increasing the load. Let's make a reservation that this is important for engines that are not equipped with the Start & Stop system.

Council number 5. Keep the speed at medium speed while driving.

The engine turbine is a unit that constantly operates at high loads, so it is impossible to drive a car with such a unit for a long time at low revs. In general, it is recommended to let the engine turbine run at extremely high speed several times a week: in this way, you will activate the cleaning process of the turbocharger boost system, which will further help extend the life of the unit. It is important to avoid "twisting" the turbine, that is, a long drive at high speeds. At the same time, the turbocharger rotor experiences increased loads, which leads to an imbalance in its operation and, as a result, failure of its components. Therefore, when driving a car with this type of engine, it is best to stick to medium speeds.

Council number 6. Do not turn off the engine immediately after stopping the vehicle.

This advice is especially important for motorists whose turbodiesel engines are not equipped with a Start & Stop system. The fact is that when the engine stops immediately, the turbine impellers still continue to rotate, but the oil that lubricates them is no longer enough, which leads to overheating of the turbocharger components (rotor and bearings). And this, in turn, leads to increased wear of these parts of the turbine. Therefore, after stopping, let the engine idle for a short (no more than 5 minutes) time. During this time, the turbine will cool down and can be deactivated.

Council number 7. Avoid prolonged idling of the engine.

For a turbocharged engine, idling for 20-30 minutes is like death. The fact is that with this mode of engine operation, coking (in other words, clogging) of the turbine, namely the oil outlet tube, the drive for changing the geometry of the turbine, can occur. Also, during prolonged idling, engine oil can be sucked into the engine cylinders, which can lead to failure of the components of the cylinder-piston group. If you still keep the engine idling for a long time, then we advise you to keep the crankshaft speed at 12001600 rpm.

Tip #8. Spend on time Maintenance car.

Follow the manufacturer's recommended intervals for changing engine oil and filters, both oil and air. Remember that a turbocharged engine tends to have shorter service intervals than a naturally aspirated engine, as the turbine operates at higher loads than a conventional diesel unit and therefore needs fresh oil and filters more often.

Following this simple advice save car owners from costly turbine repairs.