How to warm up a cold engine? Cold start and engine warm-up.

It's warm and pleasant at home, but it's cold outside, like in Russia. Just like us, when we need to get dressed and prepared to deal with this harsh winter outside, we need to prepare - the engine also warms up well. Cold start of the engine occurs in winter at much lower temperatures than in summer, so it is very important to properly warm up and drive the car during the first few minutes after starting. Insensitive handling of a cold engine greatly increases engine wear and also increases the risk of serious damage to the engine and its components.

The process of properly warming up the engine is especially important for motorists who park their dads on the street. Cars parked in a heated garage or equipped with a self-contained heater reach operating temperature much earlier and their engine is thus much less likely to be excessively worn or damaged.

The problem of cold start and subsequent warm-up is a relatively discussed topic among motorists, while, on the one hand, there are supporters of the start-up and movement theory, and on the other hand, start-up theory, wait a minute or two (clean the windows), and then go. So which is better?

Some theory

It is well known that coolant heats up much faster than engine oil. This means that if the needle of the coolant thermometer already shows, for example, 60 ° C, the temperature of the engine oil can only be around 30 ° C. It is also known that cold oil means denser oil. And thicker oil gets a lot worse/slower in the right places, meaning some parts of the engine are weaker/under-lubricated (various lube passages, camshafts, hydraulic valve clearances, or turbocharger plain bearings). Therefore, it is very important that each engine contains only high-quality and recommended engine oil. Automakers often specify in their service plans the SAE standard for a particular engine and depending on the climatic conditions in which the vehicle is likely to be operated. Thus, one oil will be recommended in Finland and the other in southern Spain. As an example of the use of the most commonly used SAE oils: SAE 15W-40 suitable for use from -20°C to +45°C, SAE 10W-40 (-25°C to +35°C) , SAE 5W-40 (-30°C to +30°C), SAE 5W 30 (-30°C to +25°C), SAE 0W-30 (-50°C to +30°C).

When starting the engine at winter temperatures, increased wear is observed compared to a "warm" start, since the piston (mainly made of an aluminum alloy) at this moment is not cylindrical, but slightly pear-shaped. The cylinder itself, made mostly of Fe alloy, has a much more stable shape depending on temperature. During a cold start in a small area, short-term uneven wear occurs. Increasingly better lubricants, as well as improvements in the design of the pistons / cylinders themselves, help to eliminate this negative phenomenon. use of more durable materials.

In the case of gasoline engines, there is another negative aspect associated with the richness of the flammable mixture, which dissolves the oil film on the cylinder walls to a greater extent, and also due to the dilution of the oil filling with gasoline, part of which condenses. on a cold intake manifold or cylinder walls. However, in modern engines with improved steering, this problem is minimized, since the control unit sensitively distributes the amount of fuel based on information from a number of sensors, which in the case of simple engines was quite difficult or. in the case of a simple carburetor engine, this was not possible. 

So much theory, but what is the practice?

Based on the information above, it is recommended to start and leave the method. The reason is that the oil pump generates a higher pressure when driving, and cold oil, which is thicker and flows, in principle, due to higher pressure, reaches all the necessary places faster. At idle speed, the oil pump generates significantly lower pressure and cold oil flows more slowly. In some parts of the engine, oil will get into some parts of the engine or less, and this delay can mean more wear. The start-stop method is especially relevant in cases when the nearest kilometers will pass as smoothly as possible. This means do not crank or understeer when the engine is cold, and drive for the engine type in the 1700-2500 rpm range. The starting and starting method also has the advantage of continuously heating other stressed components such as the transmission or differential. If, soon after starting off, an obstacle in the form of a steep hill appears on the road or if a heavier trailer is switched on behind the car, it is better to start the engine, slightly depress the accelerator pedal and let the engine run for about a few tens of seconds at about 1500-2000 rpm and up to how it starts.

Many motorists drove a vehicle that, during normal driving, began to heat up to about 10-15 km. This problem mainly affects older vehicles with direct injection diesel engines that do not have so-called electric auxiliary heating. The reason is that such motors are very economical, have relatively high efficiency and, as a result, generate little heat. If we want such an engine to warm up faster, we must give it the necessary load, which means that such an engine warms up much faster only while driving, and not idling somewhere in the parking lot.

The heating rate differs significantly from the type of engine, respectively. what kind of fuel does it burn. Despite the many improvements and improved thermal management of diesel engines, as a general rule, gasoline engines heat up more easily and faster. Despite a slightly higher consumption, they are much more suitable for frequent use in the city and in more severe frosts they also start up better. Diesel engines take longer to warm up and, from an operating point of view, they also lack various systems designed to trap pollutants in the exhaust gases. Simply put, one can write that while the small petrol engine is quite sensitive and still warms up after about 5 km of smooth driving, the diesel needs min. 15-20 km. Keep in mind that the worst thing for the engine and its components (as well as the battery) is repeated cold starts when the engine does not have time to warm up at least a little. Therefore, if you have already had to turn off and start a cold / frozen engine many times, it is recommended to let it drive for at least 20 km.

5-rule summary

• if possible, start the engine and leave it on for a few seconds
• idle the engine only when necessary
• depress the accelerator pedal smoothly, do not understeer and do not turn the engine unnecessarily.
• use high quality oils recommended by the manufacturer with a suitable viscosity
• after repeatedly switching off and starting a cold / frozen engine, it is advisable to drive at least 20 km.