Okay folks, I'm new to the board and have been reading good things about Delvac. Here is my question- Which would be better for my 2000 LS1 Firebird, 85 Mustang, and my Kia. In my 1st post I stated that I had been using 0W30 M1 in the LS1 and the Kia with no oil consumption problems. I reckon I really need to step up to 10W30 at least in the summer-right? So which is it-5W40 Delvac or M1 in 10W30 or maybe 10W40? Inquiring minds need to know from Knowlegable minds!