Mobil1 synthetic oil

While best to stick with manufacturer-recommended oil viscosity, I doubt you're hurting anything, especially since it sounds like you ran the oil through the winter in Montana. I would, however, avoid running thinner oil during the summer, especially in warm climates.

 

Yeah, I went ahead and changed it with the recommended 5w30 with Pennzoil Platinum synthetic.

 

If you read this article closely you will see the agenda is from a tree hugger's view not a true engine longevity view. the only way synthetic is cost affective in an engine is through greatly extended drain intervals and 90% of the daily drivers do not take advantage of this feature. As for racing engines depending on type of race they only run 1/4 mile to maybe 1000 miles between tear down's hardly time to develop sludge or deposits for evaluation. synthetic oil would make sense in these apps due to higher temps involved.