I dont know when last time my coolant has been change, its still gold clear color, it does not have a great sweet smell like typical prestone green coolant, so I dont know its bad or not, I test it with the sucking type hose thing and it still show at recommend range, I was thinking just take off the radiator plug drain, drain it complete and fill it with 50/50 mix coolant, but I dont know which coolant I should use.