I have a 2019 C63S AMG, which has done just under 20,000 miles, so very low mileage for a 6 year old car.

In early 2023 a coolant hose split and had to be replaced and at the same time the coolant system was filled up (obviously). I've just contacted the local garage that did that work and have been informed they would have used MB 325.6 for my car, which is pink/red. So, from Googling, I see this is the recommended coolant for newer engines and therefore all is good! Or is it?

My dilemma is that last year I noticed the engine was running hot and the fans stayed on after turning off the engine, sometimes for upto 20 mins. I could see the coolant level was down slightly, as was the oil level, so I topped both up and since then I haven't noticed any issues with the fans running after the car has been used and the engine stopped.

I'm now looking to purchase some more coolant, for use in emergencies i.e. topping up, as I always like to keep a litre in the garage. I've now realised that the coolant I used was MB 325.3 (a cheap UK brand called Bluecol). I have no idea why I would have purchased that, unless directed by a Merc dealers when I originally purchased the car!

I believe I have probably used 0.25 to 0.5 litres of this 325.3 coolant when topping up (mixed with a similar volume of distilled water i.e. 50/50) since my coolant system was refilled in 2023. I'm now reading that it's not a good idea to mix 325.3 and 325.6.

So, a couple of questions:

1. Is the top up using 325.3 likely to cause any issues? I suspect not as it was a small amount and the car has been driving okay, with no obvious heating issues.
2. Is 325.6 definitely the correct coolant to use on this model and age car? I would hope so, since this is what I was told by the mechanic, although it was 2.5 years ago when he did the work and re-filled the coolant system.

I would appreciate your feedback.

 

I also have a 2019 C63s coupe. This past February, 2 months before my MB Extended expired, I had an experienced Indy do an inspection on the car. He discovered and photographed the lower radiator hose was leaking and advised also that the radiator be replaced.
. The Dealership made the repairs as noted below.
As noted on the Invoice the Anti-Freeze used was MB 325.6.



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325.3 from what I can find is primarily for vehicles built before 2014 and mixing coolant types is not recommended as it can lead to problems with corrosion and cooling efficiency.

 

thought coolant was good for minimum 10 years?

Nothing to do with mileage but more about time as chemicals break down over time not distance traveled thru passageways inside coolant system.

 

The radiator hose that was replaced in my car was due to the pipe rubbing against something and causing it to wear a hole. The replacement hose had been re-designed slightly, so the area that rubbed was re-enforced. Clearly, this is a common issue with this hose.

 

Yes, Googling determined that 325.3 is for use in older engines and that mixing coolant types can cause issues. However, I believe both 325.3 and 325.6 are silicon based and as I only added 0.5 litre of 325.3 to the cooler system, which holds a volume of 7.5 litres, I was assuming it would be okay.

 

I've read that Mercedes recommend changing the coolant every 2 years or 30K miles. Checking through my service records, this has certainly not been done by the Mercedes dealer that has performed major services on my car! It is due another major service next year, so I will note what fluids they replace with interest!

 

Just posted this when I had the same question.


Posted at my mb dealer.

 

. This post just reminded me that maybe 2 years or so my low coolant light warning appeared. So went to local Indy/gas station where they just top off reservoir with the anti- freeze that was there. Not the MB 325.6. So I am wondering if that may have cause the radiator hose/radiator issue that I noted above? Or could it be from winter driving with salt conditions that corroded the radiator hose/radiator? Now if needed to top off coolant I will get the correct MB 325.6.



. Photo above list the MB required Service schedule. As noted: 1. Replace main circuit coolant and 2. Replace low-temperature circuit coolant every 12 years/120,000 miles.

 

Please read what I posted above. Mercedes states mixing is ok with the types they mention. They have superseded their recommendation to not mix. I was just at a dealer and went through this…I have a 2013 and always used blue and dealerships can no longer use “blue” due to regulatory issues.