I'm moving to the Rotella camp from Castrol 20W50, to T4 or T6 15W40. I'm contemplating T6 for the next change, and am wondering what others, who are using Rotella, ended up with and why?

The T6 is more expensive ($23 vs. $16/gal), but cost isn't a factor given TCO. Anyone see a downside with the T6 vs. the T4?

 

I can’t advise you but wonder why you would change from Castrol? We always ran Castrol in the fleet of family Toyotas with no trouble. Now I usually use the high-mileage 10-40.

 

Personally, I'd stick with Castrol GTX 10W-40 conventional. Have been using it on 5000 mile changes for 37 years and 483K miles with no internal engine issues. Doesn't burn enough oil between changes to even check the oil dip stick. Admittedly, it's getting hard to find as Walmart stopped carrying it. I do check Home Depot's small auto section and see it occasionally, so I stock up. If I must, I will change to Castrol Edge Synthetic 5W-40. Stick with the brand that got me here.

 

I've had good luck with Motomaster 10W30 synthetic.