My MF4610 requires 15w-40. I see people have been using Rotella 5w-40. Has anyone tried that. Summer okay, hot hay work? Is it a synthetic? any issues in newer engines?
If it calls for 15w40, any 0w40, 5w40 or 10w40 will do. They'll all be 40w at operating temperature but will be lighter at startup, which is better for getting oil quickly to the valve train.
We have run T6 5W40 (which is a full synthetic BTW) year round since our 50 Hour service. If it is good enough for a $30,000+ truck engine, it will be good for your MF.