How are you sure?I didn't run the oil 20k miles. I ran the cheap tensioner. My comment was mostly referring to German luxury car owners. I never said mine was a diesel either. I bought the car with 90k and sold it at 150k using 5w30 when it reached 100k. If 50k using w30 didn't hurt it, I'm sure it could go 150k since new. Like I said, the manual also said 5w30 was suitable.