Do you really have to warm up an engine?

Fewer and fewer new cars are being delivered with a temperature display. Even a symbol that indicates a cold engine is rarely found. Especially in winter, many people ask themselves the question: Do engines have to be brought up to operating temperature carefully? And if so, why shouldn’t you give a cold engine the spur right away? AUTO BILD explains what warming up is all about and why you should do it.

Warming up the engine: myth or necessity?

Not only regular slogans, but also many car manufacturers claim that an internal combustion engine no longer needs to be carefully brought to operating temperature. While the regulars’ slogans usually have no justification for this claim, car manufacturers justify it with the high manufacturing standards with which engines are manufactured and the choice of materials. But if you want something from your engine for a long time, you shouldn’t listen to it. Every engine should be warmed up for the following reasons in order to minimize wear.

Cold engine oil

It depends on the type of oil and the viscosity, but usually cold engine oil is much thicker and more viscous than engine oil that has reached operating temperature. While it was common practice many years ago that engines were filled with thinner oil for better cold start behavior in winter, modern engine oils are so well structured that this is no longer necessary.
Topping up engine oil

Oil is the lifeblood of an engine. When it is cold, it is significantly more viscous than when it is warm. The result: the oil film can tear off.

But even modern engine oils cannot overcome one hurdle: With a cold start, it takes a little longer for the oil to be pumped from the oil pan to the bearings and lubrication points of the engine and turbocharger. If you accelerate immediately after starting, you risk insufficient lubrication on important components. The result: greater wear and tear, and in the worst case there is even a risk of engine damage. Of course, this also applies to cold starts in summer, but especially in winter temperatures. A tip: first start the engine, then buckle up.

Those who stick to this little rule are doing a lot of good for the engine. But even if the oil has reached all the important lubrication points in the engine or in the turbocharger, the engine should not be spurred straight away. If you turn a cold engine too high, it can happen that the oil film tears off, because the engine oil is still quite viscous after all. This can also lead to increased wear and tear or to major engine damage.

Temperature differences in the engine

An internal combustion engine, regardless of whether it is diesel or gasoline, consists of well over 1,000 parts made from a wide variety of materials. But this also automatically means that the components expand at different rates when they get warm.

Increased wear on pistons and cylinder walls

This is particularly critical in the area of ​​the pistons. The pistons are heated up very quickly by the combustion that takes place in the cylinder, which means they expand more quickly, which means they become larger in size. The cylinder walls, which are part of the engine block, take longer to do this. On the one hand, this is due to the fact that an engine block is significantly more massive and can therefore dissipate the heat better, and on the other hand, it is flushed through by the still cold cooling water. The result: the clearance, i.e. the distance between the piston (rings) and the cylinder walls, becomes a little too small.
Change the cylinder head gasket

If an engine is run at high speed when cold, the pistons (rings) rub against the cylinder wall. The result: heavy wear and tear, and even major engine damage threatens.

While this doesn’t really matter at lower speeds and lower loads, it causes problems at high speeds, because the pistons expand even more at high speeds due to the higher load and the higher temperature. The result: The pistons become too big for the cylinder bores. And that means that the engine wears out faster and consequential damage such as piston tilting or loss of compression can occur. In the worst case, there is even a risk of major engine damage in the form of a piston seizure.

Stress cracks and leaks

However, the different thermal expansion can not only become a problem in the area of ​​the pistons. The cylinder head is now mostly made of a different material than the engine block. Between the engine block and the cylinder head is the cylinder head gasket, which was made from a different material. If you do not warm up an engine gently and thus do not give the components the chance to expand evenly, leaks in the area of ​​the cylinder head gasket and / or stress cracks in the cylinder head can quickly occur.
Change the cylinder head gasket

Because the cylinder head gasket, cylinder head and engine block expand differently, leaks can occur when driving at high speeds in a cold state.

Another cause of stress cracks can be the selective generation of heat. The easiest way to explain this is with the example of the cylinder head. As a result of the combustion, the cylinder head at the combustion chamber warms up more quickly, while the rest of the cylinder head is flushed through by the still cold cooling water. The same applies here: a cylinder head can withstand this at lower temperatures and low loads. However, if you turn up the engine when it is cold, there are a lot more burns in a shorter time. This makes the area around the combustion chamber much hotter faster, while the rest of the cylinder head is still quite cold. These high temperature differences can lead to material fatigue and stress cracks in the cylinder head in the long term.

Warm up the engine gently

If you don’t want your engine to suffer from all these things, you should always warm it up carefully. Compare your engine a little with yourself, because you wouldn’t like to have to sprint right after getting up. If the engine has not yet reached operating temperature, the speeds should rather remain in the lower third of the speed range. In addition, high loads such as full throttle should be avoided – Of course, this also applies to vacuum cleaners, but especially to engines with a turbocharger. When the load is high, the combustion pressure in the engine compartment rises, which is further increased by the use of the turbocharger. This also causes the pistons to expand faster and become too large for the cylinder bore. A parking heater can also help: if it is switched on, it automatically warms the engine a little.

Prohibited and harmful: let the engine warm up

Under no circumstances should you let your engine warm up while it is stationary, because not all components get warm enough and can expand as quickly and as much as they should. In addition, a mixture that is too rich is always injected into cold engines in order to bridge the condensation losses. These condensation losses are fuel that cannot be burned because it condenses on the cold cylinder walls, which means it becomes droplets again. These droplets wash – and this is particularly important for gasoline engines – the oil film from the cylinder wall and thus also cause greater wear. Warming up the engine while stationary is also harmful to the environment and it is actually prohibited.
Cold start

Do not let it warm up: If you let the engine warm up while stationary, you risk significantly increased wear and tear, and it is also prohibited.

However, if you make sure that you start the engine first in the morning and then buckle up and handle your engine carefully when it is cold, the wear and tear should be limited and you will have fun with your car for a long time.

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