>I've always used distilled water with the coolant.
Wise practice. There's enough precipitatable carbonates in drinking water in most places to really clog up fine passages.
>My question is that is the MB coolant the sam as the newer coolant called Dexcool (which is orange) that is used in the newer GM cars? I have been told that in older cars which have used the old green stuff should not use the mewer Dexcool type coolant because it can actually create sludge in the system.
Let's see if I can remember this correctly:
Both Dex-Cool and MB coolant use organic acid technology for anticorrosion. MB uses a slightly different spin on OAT called Glysantin. Dex-cool is totally nonsilicated. MB coolant has a slight silication. Classic green Prestone is heavily silicated, which is why it tends to eat water pumps.
And yes, dropping Dex straight into a system can really mess it up, especially if there is residual green silicated coolant around. The OAT will react with leftovers and turn into ugly brown sludge.
MB was twice the price of Dex last I looked. But how often does one change coolant, anyway? Even once a year, that's not a huge price hit.
That said, I have an MB V8 here which is happy after a Dex conversion (it was overheating on the Prestone that was in it when we received the car at second hand; it is now cured on Dex.)
What I was told was absolutely critical was to completely flush any remnants of the original coolant, including the often forgotten heater core contents. I did three successive distilled water flushes with a hearty hot drive in between each, and with the heater on full blast to circulate it out. By the third, the flush water was crystal-clear, no hint of any green.
I then installed 50/50 Dex/distilled. No Water Wetter used, as I was experimenting with how well Dex alone would function. Happy car. I have noted no signs of cooling system deterioration or problems at all in a year of service.