a while back i bought a 4 gallon case of d1 5w40, but having a few second thoughts about using it now in one of my cars.. engine is the old 2.5 'iron duke' gm motor - old school pushrod design, gear driven cam too (no chain, no belt). all metal gears were used in the rebuild. (factory is one fiber/one metal). it's regularly driven to redline rpm (ok, so that's only 4500rpm, it doesn't pull past that) and summer temps can get to 110*F and maybe higher. typical commute is an hour at 3000rpm. definately sees more 'abuse' than your average car. motor has 40k miles on it, all with m1 5w30, 5000mi intervals. no UOA's. lowest PSI i see on a hot summer day at idle is about 30psi. any chance that the D1 5w40 is unnecessarily thick and not to my advantage to use? any other comments?