Local garage mixes pink & green coolant in my C-Class: My learnings

Now ideally, they should have drained the whole coolant and then refilled it with the appropriate type. However, they did not bother with a coolant flush

BHPian Sanidhya mukund recently shared this with other enthusiasts.

It has been raining heavily for the past few days here in Delhi. The roads are all waterlogged and the traffic comes to a standstill everyday. Yesterday, I was stuck in a traffic jam while it was pouring heavily and the roads had become like rivers. This was when I noticed that my Mercedes C-class was displaying this warning on the instrument cluster:

This is the warning for low coolant level, so I assumed that the car could possibly have hit some debris leading to a coolant leak. I was sure that the coolant level was okay otherwise because I had it replaced at the Mercedes dealership in April 2021.

However, I found no physical leakage, so I continued driving. The warning disappeared after about 30 minutes, but I still didn’t want to take a chance, so I stopped at a petrol pump and waited for sometime for the car to cool down. I had gone away from the car for merely 10-15 minutes to attend a phone call, and by the time I was back, I was shocked to see that the fuel pump attendant had unscrewed the drain plug and had drained all the coolant! Apparently, he had a word with my driver and they somehow, without my consent, decided that the coolant will have to be replaced!

Since he had already drained all the coolant, I had no choice but to ask them to fill the coolant that was available for sale at the petrol pump. They filled in about 2 litres of green coolant and commented that they have filled it for the time being, but I will have to get it replaced ASAP since this one isn’t suitable for this car. I was already worn out, so paid up and went my way without arguing.

Anyway, since he had commented that this coolant isn’t suitable for my car, I decided to take it to a nearby FNG and get the “suitable” coolant filled. Now this independent garage has all sorts of tall claims about being “specialists” in luxury cars and even has a YouTube channel. Now ideally, they should have drained the whole coolant and then refilled it with the appropriate type. However, they did not bother with a coolant flush, and simply drained the coolant from below and filled in 4 litres of pink coolant. However, there already was green coolant in circulation inside the engine, so now my car has a mixture of green and pink coolant.

A little bit of research on Team-BHP tells me that mixing pink and green coolant is a very bad idea because it leads to a reaction between inorganic and organic components of the respective coolants, leading to a coagulated sludge being formed. This sludge can have devastating effects on your engine and the cooling system.

I will now be sending my car to the Mercedes dealership for a proper coolant flush, followed by filling of the right coolant in the right amounts. I’ll also ask them to see why this warning appeared and disappeared on its own. This was the first time I trusted a non-authorised garage with my car, and is definitely the last.

My takeaways from the above incident are as follows:

• Petrol pump attendants sometimes can have vested interests of selling their oils/coolants etc. Never let them do stuff to your car and never leave it unattended at a fuel station even for a few minutes. “We checked your coolant and the level is low” or “Your coolant is finished and your container only has water” is a very common thing nowadays. Please ignore them.
• When choosing an independent garage, be VERY careful. Rely on word of mouth rather than YouTube videos or Google reviews. These guys are thugs, they mishandle the cars (mine got damaged) and don’t even have basic mechanical knowledge. Seeing a premium car, all that they care about is milking the customer for money. Any mechanic worth his salt will tell you that one shouldn’t mix two different types of coolants. These thugs on the other hand think that it is okay to do so on someone’s Mercedes!
• Always know about what colour and grade of coolant your car uses. If possible, carry around a small container of the same.

I do agree that most of this was my fault; I was ignorant about what was going on with my car, but I was preoccupied with a zillion other things.

Recommended further read: This lovely thread by D-BHPians Vishy76 and Vigsom. It covers everything one needs to know about coolant.

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