what is the best anti freeze/coolant for 1991 525i?

Just to be clear I use Castrol oils (grade dependent on vehicle) changed at half indicated intervals, genuine coolant and PBR (Australian brand) DOT4 brake fluid changed on BMW intervals. To paraphrase the article (no author) Behr radiators supplied in the USA are prone to AlPO4 (phosphate) coating on the radiator tubes, if the wrong coolant is used. The author also thinks that the standard radiator is on the small side across the range. The BMW coolant is termed G-48 (which means nothing to me; maybe some one else knows). Behr know AlPO4 is an insulator and will cause overheating problems. Brass is not affected. IMO radiator flush compounds do not seem capable of removing the AlPO4 coating. I GUESS that anything that will dissolve the coating will also dissolve the radiator with it, but that is a GUESS. Any chemists out there??

AlPO4 is aluminium phosphate. Some investigative searching and deductive reason (surely not what I'm infamous for) brought me to the following potentially insightful article :

http://www.ehow.com/how_8442658_remo...aquariums.html

I believe most phosphates are too stable to be removed except by scrapping them off.

Cummins sells a hard core radiator flush. Perhaps it is time to check that out and see if they will sell it to the general public:

http://www.cumminsfiltration.com/pdf...LI33024-GB.pdf

Zerex G-05.

Buy the concentrate, mix it 50/50 with distilled. Perfect.