How can you tell (w/o a used oil analysis) if an engine is hard on oil? Is it mechanical complexity such as DOHC and multi-valves. Is it sump capacity? Is it a combination? The reason I am asking is my 1994 Nissan truck has the 3.0 SOHC and a total 3.5 qt capacity. Summer is coming and I am ready to get the 5w out of there. I use dino in it now but may switch to a syn such as M1 T&S. I have used the Mobil blend in 10w-40 and it did fine last summer.