Why is it just the coolant that is forcing Li Auto to proactively recall 10,000 units of the MEGA?

This is an unprecedented recall event among new - force car manufacturers.

Last week, Li Auto suddenly initiated a proactive recall. Starting this week, it will recall 2024 models of the MEGA, a total of 11,411 vehicles.

According to the official announcement, the reason for the recall is that the corrosion - prevention performance of the coolant in this batch is insufficient. Under specific conditions, it may cause corrosion and leakage of the cooling aluminum plates of the power battery and the front motor controller in the cooling circuit, resulting in the vehicle's fault light illuminating, power limitation, and inability to power on. In extreme cases, it may cause thermal runaway of the power battery.

The recall measure is to replace the coolant, power battery, and front motor controller of the vehicles for free. Li Auto said that it takes one working day to replace the parts of a single vehicle. For these more than 10,000 vehicles, the total cost of replacing all the battery packs and other components will definitely exceed 100 million yuan.

This recall is related to a recent spontaneous combustion accident of a MEGA in Shanghai. However, before the investigation of the accident is completed, Li Auto has stepped forward to admit its mistakes.

It has to be said that this attitude of facing up to the problem is really rare.

Then the question arises: Why does Li Auto have to pay such a high price, even replacing the batteries, just because of an issue with the coolant? Brother Neck talked to several industry insiders related to vehicle thermal management and found that although the coolant seems insignificant, it is actually crucial for new - energy vehicles.

As we all know, whether it is a fuel - powered vehicle or an electric vehicle, coolant is an essential thing. As the name suggests, its function is to quickly dissipate the large amount of heat generated by parts, and it also has functions such as anti - freezing and anti - corrosion.

Experienced drivers of fuel - powered vehicles should be familiar with this. Brother Neck once witnessed someone stepping on the accelerator too hard, causing the engine to overheat and smoke, and then pouring some water into the coolant and continuing to drive. (Of course, Brother Neck does not recommend doing this.)

This is because water is indeed one of the components of the coolant. Generally, the main components of coolant are two types: ethylene glycol (or propylene glycol in some cases) and water. The proportion of water is about 40 - 60%. The amount of water determines the freezing point and boiling point of the coolant.

In fuel - powered vehicles, there are not many strict requirements for coolant. Otherwise, the situation of using water instead of coolant would not occur.

After all, in a fuel - powered vehicle, the engine is the only major heat source. The coolant mainly circulates around the engine block, which is a relatively independent mechanical system that does not involve high - voltage electricity. The coolant only needs to focus on this large component. Occasionally adding some water can work for a while.

However, in electric vehicles, the battery, motor, electronic control system, and even the intelligent driving domain controller are all heat sources, and these are all high - voltage electrical components. Different parts have different operating temperatures. Automobile manufacturers connect these parts that need heat dissipation through cooling water channels to form a circulation system.

The working environment is different, so the requirements are obviously different. The biggest difference between the coolant for electric vehicles and that for fuel - powered vehicles is the electrical conductivity, that is, the ability of the liquid to conduct electricity.

Fuel - powered vehicles mainly focus on the heat - dissipation index and do not care about electrical conductivity. After all, the 12V small battery will not cause much harm. So the electrical conductivity of the coolant for fuel - powered vehicles is relatively high, about 2000 - 5000 μS/cm.

However, there are a lot of components in electric vehicles with high voltages of 400V or 800V. Once a collision causes the coolant to leak, an electric shock can be a major accident. Therefore, the electrical conductivity of the coolant for electric vehicles must be very low, less than 100 μS/cm, only a few dozen times lower than that of fuel - powered vehicles.

In addition to electrical conductivity, because there is more cast - iron material in the engine of fuel - powered vehicles and more aluminum material in the cooling system of electric vehicles, their formulations are also different.

Perhaps because this is a relatively new field, the first national standard for the coolant of electric vehicles was not released until October this year. Before that, the standard for fuel - powered vehicles in 2013 was used for the coolant of electric vehicles.

However, there is no need for us to panic. Brother Neck consulted relevant personnel from an automobile manufacturer, and he said: "The previous standard was too low, and automobile manufacturers would not follow it. Although the new national standard has been improved, generally, the enterprise standards are higher than the national standard."

With all these differences, the coolant for electric vehicles is obviously more complex than that for fuel - powered vehicles. Therefore, different from the relatively universal coolant in the era of fuel - powered vehicles, new - energy automobile manufacturers design their own coolant according to the characteristics of their own models.

Although their approaches vary, generally speaking, once an automobile manufacturer selects a certain type of coolant, it is unlikely to make changes. At least, models on the same platform will use the same coolant.

Firstly, the development cycle of coolant is relatively long, and automobile manufacturers cannot use a new coolant for each new model.

Secondly, there are too many parts involved in the coolant in the vehicle. When selecting materials for the battery system and the front and rear motors, it is necessary to consider whether the coolant is compatible.

How big an impact can this have? A R & D personnel from an automobile manufacturer directly said, "Determine the coolant first, and then develop the parts." They first determine which coolant to use, and then develop and match all parts according to this coolant.

"Because once the coolant is changed later, all the tests of other parts have to be redone, so this is basically not done. For example, if there is a leakage problem in the test of the cooling water pipe, the formula of the rubber of the water pipe will be modified instead of changing the coolant."

It can be said that the coolant affects the whole vehicle...

The tests here also include the anti - corrosion problem that occurred with the MEGA this time. Note that this anti - corrosion problem is not about preventing the coolant from rotting, but about preventing the coolant from corroding other parts.

To avoid this situation, there is a certain amount of corrosion inhibitor in the coolant to slow down and inhibit corrosion.

The formula of the corrosion inhibitor is a secret of each company. So how do we know if the corrosion inhibitor works? In the national standard, there are two corrosion tests for coolant: static corrosion and circulating bench corrosion.

Static corrosion means soaking the material in the coolant and observing whether it corrodes after 14 days of standing. The circulating bench test involves connecting parts such as the radiator, water pump, and power battery cold plate together, simulating the actual working conditions for about 40 days, and then checking the results.

However, tests are one thing, and the actual situation is much more complicated.

For example, in the national standard, only a few specific materials such as red copper, brass, and 3003 aluminum are used for corrosion tests. A cooling system engineer named A told me that the materials actually in contact with the coolant in the vehicle are far more than these. During development, they need to conduct corrosion tests on all the materials in the vehicle that are in contact with the coolant.

Another example is that the national standard requires the test to be carried out in a high - temperature environment of 80°C. Engineer A said that they also conduct a high - pressure autoclave corrosion test under more severe working conditions, adding high pressure on the basis of high temperature and using more rigorous means.

However, after all, these tests are to compress time and strengthen working conditions, using one or two months of testing to simulate the long - term use results of the vehicle. Passing the test does not mean that there will be no problems later.

In addition to corrosion, the compatibility and stability of the coolant with rubber materials are also long - term tests. From this, it can be seen that developing a suitable coolant requires considering many aspects and is not an easy task.

Let's return to Li Auto's recall this time. As the first pure - electric vehicle in the market to use a 5C battery, the MEGA has a high demand for heat dissipation. Some industry insiders believe that this may be the reason why it did not use the same coolant as the L - series models.

Currently, all automobile manufacturers are compressing the development cycle and competing for the speed of new - car launches. The coolant problem of the MEGA may also be related to the new technology and the limited development cycle.

The MEGA is standard - equipped with front and rear dual motors, both of which are in contact with the coolant. However, Li Auto's recall only involves replacing the front electronic control system and does not involve the motors. Engineer A speculates that this may be due to the different aluminum - alloy materials of the motors, but the reason may be very complex.

"Doing more road tests, covering 100,000 or even hundreds of thousands of kilometers, is the most suitable way to verify problems."

Li Auto has indeed handled this problem very efficiently. However, from the perspective of the problem itself, new - energy vehicles, as large electrified devices, cannot be taken lightly.

An insignificant part may cause a huge spontaneous combustion accident. Perhaps all of us should be more patient and careful when dealing with this new thing.

Source of pictures and materials:

Li Auto official

GB 29743.2 - 2025, "Motor vehicle coolant - Part 2: Electric vehicle coolant"

This article is from the WeChat public account "Chaping X.PIN", author: Daydream, editor: Mianxian & Brother Neck, reprinted by 36Kr with authorization.