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During my vacation, when my vehicle, a 2015 E220 S212, was stationary for the night, I received a notification from the Mercedes service shop in my vicinity indicating that the coolant level was insufficient. Due to the limited availability of coolant in the town, I was compelled to replenish the reservoir with around 400 millilitres of Organic Acid Technology (OAT) coolant. It is well acknowledged that the combination of IAT (Inorganic Additive Technology) coolant with OAT (Organic Acid Technology) coolant is not recommended. Based on my understanding, my Mercedes vehicle is equipped with SiOAT (Silicate Organic Acid Technology) or Lobrid (Long-life Organic Acid Technology) coolant, which is formulated using OAT principles. Is it OK to continue with running the 400mL OAT, which has been sufficiently diluted inside the cooling system, or is it necessary to do a flush and drain immediately? I had difficulties in locating definitive and reliable materials on the internet. To yet, there have been no observed further decreases in the amount of coolant.

Did Mercedes inform you that your vehicle's coolant level was low? How does that function operate?

The potential for digital telepathic mindreading is being considered.

When faced with uncertainty, it is advisable to do a drainage and flushing procedure. If the appropriate coolant was not available, I would have supplemented with water.

It would have been possible to augment it just with water.

Please make the necessary changes at your earliest convenience.

It is believed that the process is facilitated by the Mercedes Me platform. I get notified via email when a service is scheduled to be performed. The user makes a humorous remark on a potential surveillance situation.

If I had engaged in more contemplation beyond a few minute, it would have been evident that the aforementioned notion was indeed the most optimal course of action. I had a state of distress and anxiety as I contemplated the prospect of embarking on an extensive journey by automobile. Thank you for providing an answer.

Is it not recommended to use distilled water instead of tap water in the coolant?

Having used both options in previous instances, it might be argued that any alternative is superior than having no option at all. The use of an inhibitor will effectively prevent corrosion from occurring.

When acquiring "authentic" Mercedes coolant, the instructions provided on the plastic container indicate that it should be combined with regular tap water. The term "distilled" is not clearly used.
One possible reason is because the coolant composition effectively inhibits corrosion. Another reason is that some cars have a level detector that quantifies the Ohmic resistance present in the coolant. Distilled water has a significantly elevated level of resistance. Tap water has a comparatively lower resistivity. The use of distilled water may potentially lead to the occurrence of erroneous level warnings.