I've been using Zerex G-05 in pretty much everything for quite some time now. This is a thread I started about 9 years ago > (Is G-05, a good "one" coolant solution?) I haven't had any problems with it. It's coolant change season now, and I wonder what has changed in the last almost decade. In looking to buy my trusty Zerex G-05 concentrate, and I see for whatever reason, the Zerex Heavy Duty Extended Life coolant concentrates are much less expensive., and has a claimed longer service life, at least in the nitrate free formulation. It's available in yellow (nitrate free) and red (nitrated). They are clearly marketed to the heavy truck and equipment market, but what qualities would make these coolants inappropriate for passenger vehicles? Are either one of these a better choice than my existing G-05? Is either one compatible with G-05 if not fully flushed? How about with a complete flush? Thanks, I more curious than anything else.