Audi Repair: Used incorrect radiator coolant in 93 Audio 90CS, antifreeze coolant, radiator coolant

Question
I would like to thank you in advance for any suggestions you may have to the following matter.

I recently bought a '93 Audi 90CS, my first Audi.  Today a small hose under the overflow reservoir burst while my wife was driving it.  I left work, replaced the hose, and filled it with a 60/40 solution of Prestone® Extended Life Antifreeze/Coolant, which claims to be compatible with ANY antifreeze/ coolant – regardless of color.

Fortunately, this evening I discovered your numerous responses in this site.  I now believe I should have used a coolant specifically formulated for an Audi/VW.  I believe this is the Blue version.

I am concerned that my mistake may be causing some serious corrosion issue for the cooling system.  I assume I need to completely purge the cooling system and refill with the proper fluid.  I'm just not sure how quickly this needs to be done and if there are any methods for doing this that are specific to this vehicle.

Do you mind letting me know what the best course of action is to resolve this problem?

I plan to purchase a repair manual over the Internet as none of the local repair shops seem to carry manuals on Audi.

Thanks again for any suggestions you may have to this question and also for the significant time and effort you have afforded everyone else on this site.

Answer
Hi,  thank you for your question.  For a 1993 90CS, the different metals in the engine can give rise to premature corrosion if the wrong antifreeze is used.  Personally I think that if you used a brand which is "Safe for all Engines" then it should be just that, if there was a serious issues, then it would say "safe for all engines except Audi's"  Think of the power steering fluids, which do in fact state exactly that, and is much more sensitive on your car.  It may be worth a phone call to the manufacturer of the antifreeze you used; I would say that the urgency level of this is not the highest; if they do state that it may be incompatible, then it is best to drain the whole system, which means locating the drains on the engine block and the bottom of the radiator.  Once drained, flush the system with clean water and then let it drain again; then refill with the recommended fluid and bleed the air from the system as per the manual.  Good luck,  Jan