Maybe 15-20w and I can't see any issues with vanos etc as you're still in the range (starting viscosity), just a bit narrower.
I also don't see how going above 40w is going to help? Is your motor overheating? I don't think I'd go as thick as 50 myself.
Try watching this
https://youtu.be/48pviPLgaPQ?si=jFG6OG8oBkCxEOD7
Quote:
20W-50, 5W-30, 0W-20... These viscosity grades are all available at the local auto parts store, but a 0W-20 is not a Zero Weight oil. The "W" in 0W-20 actually stands for Winter.
Because viscosity is the most important characteristic of any lubricant, understanding SAE grades is critical to optimizing engine performance and durability.
World renowned Tribologist and Certified Lubrication Specialist, Lake Speed Jr explains the SAE J300 viscosity grade classification system in this video.
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