gosney,i own a 2004 trailblazer LS with 164000 km,s on it and i just use reg mobile 1 oil,all is well so far, but im sure others here will help you out.
i use synthetic in my 91's10 but thats only got 64,000 miles on it. but if you do start to use synthetic, do not switch back to conventional, because its bad for the motor. hope this helps
Just make sure you use an oil to the manufacturer's recommendation. I believe by 03 GM was on 6094M which most semi-synthetic and full synthetic 10w30's meet or exceed. (They usually say right on the bottle) IMO if you change the oil yourself I recommend mobil 1, it has a fairly low ash content compared to most (less than 1%), and can be bought cheap, but is frankly over priced at a quick lube shop.
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