This is from a GM EMD Locomotive Maintenance Instruction dated 1991:
Also, I found this from GM TSB 83-I-26 dated 01/17/1983:
So it seems that there were once high-silicate formulations that were designed to protect aluminum engines. The only reference I've found to silicate levels found in these coolants is a patent from 1985, which suggested that levels of 1400ppm in undiluted coolant were typical (resulting in 700ppm in a 50/50 mix).
Given that any IAT silicated coolant you buy these days will have a max silicate limit of 250ppm because it meets ASTM D4985, has the need for additional silicates for aluminum corrosion protection been determined to not be required?
SILICATE DROPOUT
With the increased use of aluminum in automobile engines, many of the antifreeze coolant manufacturers have
introduced high silicate antifreeze formulations. The primary purpose of the new formulations is to prevent
corrosion of the aluminum heat rejection surfaces as well as other aluminum parts.
Also, I found this from GM TSB 83-I-26 dated 01/17/1983:
Chevrolet Motor Division has in past model years recommended use of ethylene glycol base anti-freeze that meets GM Specification 1899-M. This recommendation has changed for 1982 and 1983 vehicles which are factory filled with coolant which meets GM 1825-M specifications. It is required that any additions of coolant to these vehicles be done with GM 1825-M. This change was necessary due to the use of aluminum components on some engines which required a different formulation of anti-freeze to prevent corrosion. This anti-freeze is available from WDDGM in gallons and drums as P/N 1052753 and P/N 1052754.
So it seems that there were once high-silicate formulations that were designed to protect aluminum engines. The only reference I've found to silicate levels found in these coolants is a patent from 1985, which suggested that levels of 1400ppm in undiluted coolant were typical (resulting in 700ppm in a 50/50 mix).
Responsive to such increasing use of aluminum, manufacturers of coolants for internal combustion engines have generally increased the silicate content therein. Silicate levels in many commercial coolants have increased about three- to eight-fold in the past several years. A typical undiluted coolant contains about 1400 ppm silicate as SiO2.
US4707286A - Coolant stabilizer - Google Patents
A stabilizer for glycol or glycol ether based aqueous coolant compositions comprising a combination of certain organic phosphonate compounds and certain organic silicon compounds, and coolant compositions containing such a stabilizer and methods of stabilizing coolant compositions by the...
patents.google.com
Given that any IAT silicated coolant you buy these days will have a max silicate limit of 250ppm because it meets ASTM D4985, has the need for additional silicates for aluminum corrosion protection been determined to not be required?