In 1991, the GMC K1500 had four engines to choose from. The base truck included a 4.3-liter V-6 with 150 horsepower and 230 foot-pounds of torque. Available as options were a 5.0-liter V-8, a 5.7-liter V-8 and even a 6.2-liter, diesel V-8. All of the gasoline engines shared oil requirements, but the diesel engine had its own specific oil needs.
In all of the gasoline engines, GMC said that 5W-30 engine oil was the preferred oil in all temperatures, but you can opt for 10W-30 if the outside temperature did not fall below 0 degrees F or SAE 30 oil if the temperature stayed above 39 degrees F. In the 6.2-liter, diesel V-8, GMC said that 15W-40 diesel engine oil was preferred, but you could opt for SAE 30 if the outside temperature stayed above 32 degrees F or 10W-30 if the outside temperature stayed above 61 degrees F.
Including the oil filter, the 1991 GMC K1500 pickup's gasoline engines all held 5 quarts of oil. The 6.2-liter diesel engine held 7 quarts of oil.
