OK - understood. The question is: any brand recommendations? I assume that all "heavy duty" coolant is not the same?
Experience? Brand recommended / to avoid?? Thanks!
A heavy duty truck forum would yield better information.
In the US and UK, heavy duty means it passes ASTM D 6210 and in general contains nitrite to protect the liners (though this can be done with other chemistry). It can be green or any other color, though generally the conventional life coolant (3-5 years) will be green and the long-life (5-7 years) will be red. While many will rave for long-life coolant, on an older engine with a history of conventional products (Prestone green) there is NO reason to believe a long-life product will be better than a conventional. In fact, there is considerable reason to believe it will be worse, as the inhibiting layers are different.
BTW, some OEMs still use conventional coolant for factory fill, as some large trucking companies request it that way. It is NOT obsolete, not like conventional automotive coolant is.
Good brands? In no particular order, Fleetguard, Texaco, First Brands (Peak), Penray, Recochem, Dober Chem, Caterpillar, Prestone (they make a good HD line), and a whole bunch of others. Many are relabeled for other folks. All of these make both long-life and conventional coolants.
Get any salt water (~ 150 ppm) in ANY of these and they are immediately condemned.