What type oil to use for 1999 suburban lt 1500?

Answer 1

It depends entirely on the condition of your engine. If the bearings are in good condition, use a lighter weight oil (lower numbers). If the bearings are getting a little worn, use a thicker weight oil (HIGHER numbers). Watch the oil pressure gauge. If, after the engine warms, the oil pressure starts to drop to near zero during idle, use a thicker oil. If the oil pressure stays up when the engine is warm and idling, you might be able to use a lighter grade oil. As related to the brand, use whatever has been running in the engine in the past, so long as it's a respected brand with the SAE certifications.