Again, it is religion. Some owners use Zerex only as this saves $5 over MB coolant.
I read too many topics with engine overheating issues and too often it turned out Zerex was involved.
Maybe my impression is biased, maybe not, but for 5 bucks I am not going to Guinea pig.
Thanks Kajtek1. Very interesting discussion. This forced me to take the time to look closely at this. The guys here may already know what I'm about to spew. I'll just go with the MB fluid... if I can. I'm not that interested in the $5 savings... obviously. My only coolant flush that was done at this point was done by the dealership many miles ago (at least 4 years ago perhaps), so yes, they used MB coolant. It is green, so it is the 325.0 spec that is equivalent to G-05. Below is the spec sheet from the manual. At the bottom, it shows the Zerex fluid, which is part of the MB spec.
As far as cooling goes, all the MB spec coolants are 99% ethylene glycol, minus the water, with the 1% being additives. So the heat transfer capability of each one is identical. Zero difference. So the only thing that can make for a problem is the additive package, which is about anti-corrosion and anti-oxidation.
If you get incompatible additives, you can have a BIG problem. Zerex G-05 uses a HOAT additive package, as does the MB 325.0 spec fluid. But it does appear that the the newer 325.0 MB fluid is akin to the Zerex G-48 spec, both of which also use a HOAT additive package. Regardless, all should be compatible and not cause any reaction with each other, as they are on the factory spec list. Is one as good as the other for protection? I don't know.
One thing to be careful of that I need to look into more - The newer MB coolant that is pink (325.5 spec) that uses a Si-OAT additive package that is NOT compatible with the original 325.0 spec coolants that use HOAT additives. It does look like I can get the 325.0 spec from FCP Euro, so it must be available. It is the Blue, so it is the G-48 equivalent.
But point taken and I'll do a bit more research.