1994 GMC 6.5L Naturally Aspirated Diesel K1500
When I got to the parts store for oil the tell me to get 10w-30 for my 6.5L diesel but thd oil cap says 15w-40 which would be best option
I run Rotella 5-40 synthetic in almost everything I own!I switched to Rotella full synthetic. I seen better mileage with it and when I had the head gaskets go, I was told that is what saved my motor from the coolant damage. I was changing it every 7000 miles. Then had the oil tested at 6000, 8000 and again at 10,000 and it came back good each time. They said I could go around 20,000 miles. I stuck with the 7000. I can tell you that if you use the Rotella T from Wallies, don't let it puddle on a smooth garage floor and step in it. There are some body parts that don't like being slammed onto a concrete floor that hard.