I just found this forum and instead of changing the water pump on my daughters '98 Blazer I will first try back flushing the heater core. Glad I read the dexcool stuff.
My problem has been a persistent P0173 (bank 1 rich) code. It has been intermitted since around 70,000 miles. It is a 1995 4.3L . I have an auto x-ray scanner. Both O2 sensors and EGR valve have been replaced. It seems to light the check engine light after highway driving more the 2 hrs. I do not see any decrease in performance or fuel economy. I currently have about 90,000 miles on it. Any Ideas ???