Notice that 30 weight is not listed in the original specs.
Why? A joke:
"The number before the W of a multi-weight oil (or the only number of a single weight oil) is the time in seconds it takes for full pressure to reach the farthest bearing in the engine".
5W30: 5 seconds
20W50: 20 seconds
50: 50 seconds
As mileage increases leakage from the bearings, it takes even longer...
Heavy weight oil is a good idea, if the oil and the engine are both at 212 degrees when you start it.
