I've got a '98 GMC 1/2 ton with the 5.7 engine with 182,000 miles. What I'm wondering about is whether or not to use 10W-30 or 5W-30. 5W-30 is the spec, but with the miles that are on it would it be advisable to use 10W-30? Any knowledgeable input is appreciated. The prior owner had been using 10W-30 Mobil 1. I use Mobile 1 in everything else I have, so that's what I'll be using in this.
Ken
The main reason 5W30 is factory spec oil is to gain a tiny amount of fuel mileage increase for the EPA mileage test stats to increse the overall CAFE rating for the manufacturer. I've used 10W30 on my GM trucks and cars after the first change. In winter I go the 5W30 because it dips to -35 here and typically is -10 to -20 for three months. If it rarely got below freezing I wouldn't even do that. I just go to Wally World or Target and buy the no-name stuff.. As long as the oil has the approved API level certification (SJ, for example) it meets or exceeds the manufacturers standards. I change both oil and filter every 5000 miles in warm weather, every 3000 in winter.
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