I've owned my 2003 GMC Sierra 1500 with a 5.3L Vortec since brand new. It had nothing but 3k Conventional 5w-30 OCI's up to 63,000 miles. It had nothing but 4-7k Synthetic 5w-30 OCI's up to the last fill. Then, knowing the stout additive pack, and knowing I'd pull my heavy boat a lot, I thought what the heck: I filled it with Mobil 1 Turbo Diesel Truck (TDT) 5w-40 last Spring, close to 200,000 miles. - On 5w-30: Each cold start for years (at 32F & under), the engine would clack like crazy until it warmed up, then it slowly went quiet. - On this M1 TDT 5w-40 fill: Each cold start (at 32F & under), there is NO engine clacking. I have repeatably started this engine in cold weather to prove eit's consistent. It sits and sat outside for the past 5 years. It's 7F this morning and it started quiet as can be (and has all this season). ...and before anyone gets on this kick... I have had zero bias on engine weights. Amazing.