I have over 400,000 miles on my 2000 Silverado 4.8 engine and in the last three years my oil pressure has gone down to about 20psi at hot idle now with a little more cold start noise . I Have been using mobil 1 10w30 extended performance and was wondering if I could blend in some of their new 5w40 blend with it to help bring back some pressure and prolong the life a little. Im not sure which of the mobil 1 blends are compatible or incompatible, I was told that some blends would cause separation