My coolant temp was 10* hotter going from Joe Gibbs 10-30
synthetic Hot Rod
oil to Gibbs 15-50 conventional. My
oil temp went up accordingly. My
oil pressure also went up 5lbs. because of the resistance that wasn't needed. ( stock clearances)
I am now back to Joe Gibbs 10-30
synthetic.
Go to a lower viscosity oil within the limits of adequate oil pressure and the temps will come down.