Since I am doing a valve job on my '90 300E, and I have to replace the coolant anyway, is there any particular coolant that has to / should be used in these engines ?

 

Yes, the antifreeze must be an HOAT (hybrid organic acid technology) type. Valvoline Zerex G05 is what you need. It's the same thing as the MB dealer antifreeze, but cheaper, and available at most auto supply houses.

 

Thank you.

 

I'd stick to MB dealer coolant. It's pH neutral and, according to those who know better than me, that is important. It's hardly a large outlay, even if it isn't as cheap as alternatives. However, if it really is 100% identical to Valvoline Zerex G05, then fair enough.

 

do a coolant flush first to get rid of all the built up corrosion and junk in your system. then add zerex and water, 50/ 50.