Should I warm up the engine?
There are as many opinions on this issue as there are people. Some argue that you need to warm the engine to 40oC only in winter and then go, others — that up to 40-50oC warm and summer and winter, others just start the car and go. There are claims that do not need to warm the revs started to fall and all need to go slowly, because other nodes are still cold, that's all and heat. Let's try to understand this issue in more detail.
The operating instructions and service book supplied with the car say different, especially over time:
Previously, twenty years ago, the instructions were written clearly: "it is not recommended after starting at low temperatures to warm up the engine on a stationary car." It was recommended to do it in motion, with minor loads.
Then the instructions began to write: "Quickly warm up the engine when driving . Use the maximum engine power only after the operating temperature has been reached." And here is unclear - is it possible to stand up to warm the motor up to 40 degrees, then slowly moving to heat up to operating temperature. Or starting revolutions went down to idle - and all, went, without using the maximum power?
If you look in the service book, for example, Mercedes-Benz, there you will find the phrase: "do Not warm up the car during Parking" (see photo on the right). But then you need to pay attention to where this phrase is printed in the section on the protection of the environment, so there is an obvious concern for the environment.
So the manufacturers have not given us clear guidance.
What is dangerous with the cold start and the subsequent warm-up of the engine:
- increased wear of engine parts in friction pairs, the gap in which differs from the design (both in the larger direction, for example, in the piston-cylinder wall pair, and in the smaller, for example, in the piston-piston finger pair);
- insufficient supply of oil to the friction pairs in the first seconds of start-up and after start-up, especially in remote oil pipelines;
- the negative impact on the engine oil - here and getting into it a large amount of unburned fuel, combustion products through the increased gap between the piston and the cylinder; water ingress as a result of condensation of the engine.
From all of the above, it can be concluded that the faster the engine, and hence the engine oil, warms up to operating temperature, the less engine wear and the correspondingly less will be the consequences for the oil. So, the speed of warming up of the engine depends on:
- serviceability of the thermostat. Settings clearly vary from car to car, but it must be native and working - it is assumed that for example, at -20oC coolant uniquely circulates in a small circle;
- the material of the cylinder block or cast iron (for example ОМ601) or aluminium (like the M113). Obviously, the aluminum block will warm up faster;
- engine oil viscosity - the thicker the oil, the greater the friction and rolling resistance it creates, the faster the heating;
- fuel quality. If we are talking about gasoline, an important indicator is the evaporation temperature of 60% of the volume of gasoline. The smaller it is, the easier it is to evaporate the gasoline, the more it will burn. In addition, the amount of heat from the combustion of such fuel is much more, and accordingly the engine will warm up faster;
- availability of pre-heater;
- driver behavior – or you immediately turn on the stove, taking the heat from the engine, or stand before the "tropics" in the cabin, or warm up 30 seconds and drive as soon as the speed fell a little and continue to warm up in motion.
Low-temperature performance of engine oil
Let's make a small digression in the field of terminology, in order to clearly understand the essence of the terms relating to low-temperature moments. So, there are temperatures:
- solidification, otherwise Pour Point - the temperature at which the oil ceases to flow and it can not be poured from one container to another. For example from the canister to the engine. Not to be confused with the temperature of "freezing". In petrochemicals, the term "freezing" refers to light petroleum products, such as diesel fuel, "solidification" is applicable to oils. Often in the information sheets manufacturers indicate some crazy temperature Pour Point. There are also indicators of minus 54oc. This does not mean that at this temperature it is still possible to start. No and again no. The pour point is generally below the pumpability temperature by 5 oC. For reference: when the temperature decreases by 5 ° C, the viscosity of the engine oil increases by about 2 times;
- the limit of pumpability - viscosity characteristics of the oil at low temperatures and low speed of shift of an oil layer. Below this temperature, the oil pump simply will not be able to pump oil from the pallet and push it along the oil lines, i.e. we will get dry friction and the death of the motor. According to the SAE standard, the pumping limit is the minimum temperature at which the viscosity of the engine oil is not higher than 60,000 MPas, providing pumping through the oil system). The pumpability limit is usually 5 degrees above the pour point and 10 degrees below the cranking limit;
- cranking limit. Checked on a "cold crank simulator" CCS (Cold Cranking Simulator). Is 6200 MPas for oils 0W-XX at a temperature of-35 ° C; 6600 MPas for oils 5W-XX at a temperature of-30 ° C; 7000 MPas for oils 10 W-XX at a temperature of-25 ° C. In fact, these values do not mean the minimum temperature at which it is possible to crank the pin shaft. The cranking temperature is a very conditional value, which means that the starter is able to spin the crankshaft to the starting speed, i.e. a successful start is achievable.
What happens to the engine when working with low oil temperature?
Let's try to understand what happens to the engine, its internals, at low-temperature start-up. And in General, what is considered a low-temperature start? It is clear that starting a conversation about the oil, we mean the absolute serviceability of the battery, starter, ignition system and fuel. We believe that the fuel also corresponds to the season. I. e. start itself should happen without problems. Consider two cases of cold start:
- the temperature of the air, as well as the engine that has had time to cool down normally during the night, is equal to or below the so-called cranking limit. OK! Somehow managed to scroll - for example carrying the car on a tie. But this does not mean that everything is in order: if the oil temperature is below the specified (see above) another five degrees, then we are stuck in the so-called pumping limit, i.e. the viscosity of the oil reaches a value of 60,000 MPa. This means that the oil can not be pumped by the oil pump through the oil channels to the crankshaft bearings, in the timing mechanism, does not fall on the cylinder walls and pistons. I. e. the engine will just die. Yes, I saw and blowtorch under Carter and boiling water in the engine, but You need it? I think, understanding the consequences, it is better to sit at home at such temperatures.
- the second case is when the temperature of the oil (ie engine or outside air) cold winter morning above the temperature of provorachivayut. It is clear that the situation is the most common, because everyone who lives in regions with cold winters for these winters prepares and uses oils (by their own decision or the advice of older comrades), able to ensure the launch at the lowest temperatures, which can only happen in his hometown. It is believed that a confident start can be provided with an oil viscosity less than 6500-7000 cSt . In this case, and disagreements - you can (or need to) immediately after you start to start a movement? Or need a long warm-up to the operating (or acceptable) temperature?
So what happens to the engine and the oil in it during the cold start? What can be dangerous cold start for the engine?
- long time of filling the oil lines of the engine. The essence of the process: if you take the power of the pair "battery+starter" at a temperature of +20 ° C for 100%, at a temperature of-30 ° C it will be only 20%. I. e. the starter will slowly rotate the crankshaft, start in such conditions, taking into account the reluctance of gasoline to burn at such temperatures will occur later. And all this time the barely rotating oil pump will work with low productivity, which will lead to a slow increase in pressure in the oil system. And the pressure I needed! From the hydraulic point of view, a friction pair (e.g. connecting rod or main bearing) can be considered as a gicler, through section. It is known that the flow rate (read flow capacity) through the passage section is directly proportional to the cross-sectional area, the pressure difference "before-after" and inversely proportional to the viscosity of the liquid. Well, the cross-sectional area does not change with temperature, but the low pressure in the oil system (we are talking about the first seconds of operation, when the starter barely turns the crankshaft) plus thick oil will lead to the fact that the oil through the liner will pass much less than necessary. The result may be a rupture of the oil film and dry friction, ie bullying on the crankshaft. In engines M278 Mercedes did interesting - installed on the oil supply line to the cooling nozzles of the piston bottom shut-off valve, which at low engine temperatures blocks the supply. Killed "two birds" - turns off unnecessary consumer of oil and the pistons warm up faster. Of the minuses - removed the extra source of heat for the fastest heating oil;
- then the oil begins to heat up and it is heated the more intense the oil is more viscous. Relatively speaking, when using 10W-40, the oil itself will warm up faster than 0W-40 . But here we are faced with another feature of the Mercedes-Benz engines: with rare exceptions, all of them are equipped with water-oil heat exchangers. This heat exchanger is an additional point where the oil loses much needed heat in this situation, giving it much slower than the heating coolant. Therefore, on machines with such a heat exchanger, the oil is heated much more slowly. So, the more viscous oil is used in the engine, the faster the oil heats up: the more viscous oil causes high friction in vapors. It should be noted one thing – the influence of the presence of fuel in the oil. Very often it is necessary to hear stories that on oil 10W-40 or even 15W-40 the engine is quite good started at temperatures minus 30 and below. Owners of these cars it makes sense to think:
- if 5.5 liters of engine oil M271 gets 500 ml of gasoline, the viscosity of the oil at a temperature of 40 ° C will be only 43% of the viscosity of pure oil;
- if in 5.5 liters of engine oil M271 gets 350 ml of gasoline, the viscosity of the oil at 40 ° C will be only 50% of the viscosity of pure oil;
- if 5.5 liters of engine oil M271 gets 190 ml of gasoline, the viscosity of the oil at 40 ° C will be only 63% of the viscosity of the pure oil;
- if 5.5 liters of engine oil M271 gets 100 ml of gasoline, the viscosity of the oil at 40 ° C will be only 78% of the viscosity of pure oil;
- if in 5.5 liters of engine oil M271 gets 44 ml of gasoline, the viscosity of the oil at 40 ° C will be only 87% of the viscosity of pure oil;
Moreover, 10% of the fuel caught in the engine oil, after 24 hours of engine operation will not turn to zero, but only 0.7...1%. I. e. fuel evaporates extremely hard.
- the gaps in the pairs and joints of the engine are far from calculated. Let's say a couple of "piston-sleeve" gap doubled against the nominal (specified for the build process, i.e., at +20oC). You understand that the calculated, ie at operating temperature the clearance is even less. But in a pair of "piston finger – piston" on the contrary - the gap tends to zero, ie we are talking about "snack". I guess all I have noticed that after low-temperature start of the engine is much louder. This is the result of working with non-design gaps, which eventually leads to excessive wear of the engine. It is believed that one warm-up from "- 30" to operating temperature takes away from the engine life of about 500 km.
How to warm the engine?
For AMG vehicles, it is not recommended to enter power modes until the oil temperature reaches 20 ° C. If the AMG oil temperature is displayed by the on-Board computer, conventional machines are deprived of such a system. But if you use these recommendations, it turns out that the AMG engines, which are allowed to fill only with oil 0W-40 or 5W-40, at 20 ° C overcome the viscosity of about 200...300 cSt. So we understand that at viscosity of 200...300 SST we have every right to ship the motor to the full, without fear of damage or destruction. Another thing is that this viscosity is achieved for other oils at very different temperatures. Since the viscosity change curves vary greatly in temperature from oil to oil, we assume the following assumption:
- XW-30 oils allow to pass to the mode of movement with high loadings at an oil temperature of 10-15°C;
- xw50 oils will have to heat up to 30 degrees, and XW-60 - up to 40°C.
AMG owners are good - you can just look at the display to see when you can "flood". What do the simple folk on the "civilian" cars? After all, the temperature of the oil is not equal to the temperature of the coolant! Output - warm the engine with a "margin" - up to 40 degrees (meaning the temperature of the liquid in the cooling system). This is usually the beginning of the temperature gauge scale. Ie arrow or the column steel above $ 40 - and you can "tap along".
So, we got three reference points of the engine oil warm-up modes:
- minimum engine oil temperature at which safe start-up is possible in principle;
- the point at which the engine can be output to power modes without fear of damage. It is clear that we are talking about the second phase of warming - warming up in motion. The point is that this phase is also divided into two parts - in the first part we are "sick", not raising the speed above 2000-2500, until the oil temperature reaches 20oC. In the second part of the warm-up in motion, we can afford to add gas and even overtake the bus;
- well, the third point - the operating temperature, when the oil temperature is equal to or slightly above the heated to the operating temperature of the engine;
- And here is where you need to find the fourth point. This is the temperature to which you need to bring the oil before you can start moving. Theoretically, this value can be found, calculated, logically assumed. But it will still be individually for each engine, depending on the material of the cylinder block, boost, oil, of course, and many additional parameters, and even a bunch of variables because there. Even if we derive a hypothetical temperature to which we are waiting for warming up on a stationary car, and then – warm up in motion. But very few cars have an oil temperature gauge except for tuned models. And to compare it with the temperature of the coolant means to make an additional error.
At this stage, we return to the polar points of view:
- warm not - start-revs dropped and went;
- warm up at idle speed at least before the coolant needle moves from the stop
- Well, some warm up to operating temperature.
Option to heat only in the movement
Has a right to exist - in the instruction manual said so, but:
- the phrase "do not warm up the engine during Parking" in the instructions of the plant is rather environmental in nature. Indeed - a rich mixture, incomplete combustion of fuel, not released on the temperature catalysts and lambda probes - all this leads to increased emissions into the atmosphere of the waste products of your motor.
- it is said about a faster warm-up of the engine in the driving mode. But I'm sorry, how does this usually happen? You start to go and realize that you do not see where you are going. The next logical action is to turn on the fan and heater to the full, in order to somehow provide a safe overview. But this way You take away the heat from the engine, thereby slowing down the heating process. I think many people noticed if you live a few kilometers from work that arrived, and did not warm up the car to the end during the trip. Is it a quick warm-up?
- OK, started up, left the yard, drove to the intersection and... have become in cork. Probably 80% of the time you're standing in it, i.e. idle, sometimes tearing forward, not to let another stupid boor climbing in front of you. It's warming up in motion?
- ask yourself the question - why the engine in motion warms up faster? That's right - because a load more! Thus, we try to avoid wear and tear as a result of slow warming up on a standing car, risking damage to the engine as a result of working with high loads on cold oil! And it does not avoid wear; Moreover - wear in this case is more intense, just reduced in time. In the equation "long but relatively small wear" and "intensive wear over a short period of time" can be put equal to;
- in addition to the engine, let's remember about such a unit as an automatic transmission, which is not less dependent on temperature. High loads at low oil temperatures can damage the torque Converter wheels. That's one. The second - in the brains of the engine control units has a function quick warm-up systems of neutralization of exhaust gases, which switch to high gear takes place at higher revs (I think many have noticed that in the cold box is "addictive", and switch much later, and often not comfortable with the shot). A trifle, but not the most useful for the health of the box;
One caveat: when warming up on a standing car engine oil itself suffers much more. Unsteady gaps in the CPG provoke a greater breakthrough of moisture, fuel combustion products and unburned fuel into the sub-piston space, i.e. into the oil. Therefore, supporters of a long warm-up, it makes sense to think about an extraordinary oil change with the onset of heat.So, on one side of the scale we have long-term wear plus environmental damage, plus disgruntled neighbors, where we "bask" under the Windows. On the other, the same wear but more intense, with the risk of engine damage (if you do not understand where the boundary of the "movement without load"), but shorter in time plus the discomfort (beautiful pictures of the frost on the glass, the peculiar feeling of the leather seats like you snowman fucked in the ass well, etc.). Conclusions? Very simple - from the point of view of the life of the engine there is almost no difference in the way of warm-up on stationary cars or on the move. All disputes, years of lasting among motorists, and then on the forums is akin to golovanovsky problems which end to break the egg. And there is no middle ground.
What is a cold start?
Let's try to understand for yourself, what temperature is the threshold above which the ongoing debate about the need or the dangers of excessive heating on the vehicle is stationary? Zero degrees? Or minus 10? Or minus... Maybe it depends on the viscosity or quality of the engine oil?
In fact, it does not matter at a temperature of-20oC You start the engine or at +20 - the engine works with no design gaps and we have all the same wear, albeit much less at plus temperatures. The fact that You are not cold does not mean that the viscosity of the oil has reached the estimated 10-20 cSt, which is designed for the ideal engine lubrication of all pairs. Warm the engine is necessary and at start-up in plus 10. It is clear that a long warm-up on a standing car is simply inappropriate, but some short time is still required to warm up the oil.
We conclude - still need to warm. Question - how? If simply following rules should be followed:
- always keep the battery, fuel system and ignition system in perfect condition;
- try to refuel only on proven gas stations;
- fill the engine with oils corresponding to the viscosity characteristics. They should correspond to the expected winter in the region of Your residence;
warm up the engine on a standing car is necessary. But this should be done without heat in the heating system (stove should be off). Warm-up time in this phase - at Your discretion - from 5 minutes (if frost -15 and above or oil is used 0W-XX) to 10 minutes. It can be heated until the coolant temperature indicator needle comes off the stop;
- further heating - in motion, according to the recommendations of the manufacturer. First, without load, slowly pouring in the ranks of the same as You, seeing nothing through the frosted window. Then, when the oil temperature reaches 20 ° C (on AMG-shnyh motors software removed "limiter" loads - you will feel it yourself. On conventional engines, where there is no eradicates or oil thermometer - on the behavior of the arrow of the pointer of the coolant. It should break away from the stop (unless You did it on a standing car, Smoking, scraping glass, swearing at the climate, the country, the parents who gave birth to You not in California, but here, etc.).);
- then - until the engine reaches the operating temperature, gradually increasing the load on the engine.
Do not forget about the viscosity - the engine is designed to work with oil viscosity of 10-20 cSt, and already at a temperature of 40 ° C it is under the cell, i.e. 5-10 times higher. Any deviation in the operation of the lubrication system can lead to a violation of the conditions of the integrity of the oil film, and hence to dry friction = engine wear. By the way, in Formula 1, the oil is poured into the engine already hot at the last moment, so that it works perfectly and immediately in the calculated gaps - that's how serious this is. So take care of Your motor during cold starts.
The article from the site benz-club.org is taken as a basis