I have been using mobil 1 clean 5000 for 5 years now? yeah sounds right. same with a mobil filter. on my green OBS i had a slight itty lifter tick. i wonder where i put the pics of the inside of the top end when i was doing work but under the valve covers, clean. when i had the pan off, just the usual brown tinted metal but absolute no spot of varnish or sludge. that and i change it every 2k miles(its about 3 months driving for me). in my 07 NNBS same oil same interval. pull the stick and it looks pretty good. at 2k miles im at the same level and put new oil in, usually gotta use a flashlight to find the oil mark cuz its so clear. working at jiffy for 3 years you start to laugh when you put fresh oil in a car and you run it check the stick and its black or brown already. the thicker the oil, the harder it is to push through your push rods and bearing holes in the rods. However, the better it works at keeping itself between the bearing and crank journal. my thinking is you run heavy oil in a diesel for its thermal attributes and since its thicker its harder to squeeze out of bearing journals under boost. Just my thought, but the diesels i would think have larger, much larger, orifices for oil to pass through. newer cars are made under muuuch tighter tolerances(like bearings tolerance) and thus only need 0w-30 or 40. that and its 1-2% more efficient since the engine fights much less to pump thin oil around it comes out to better efficiency, heat transfer, lubricity and anything else the scientists say did you know jiffy lube is owned by pennzoil, and shell owns pennzoil. crazy.

 

I've put my trucks (and cars) through some brutal driving conditions, the likes which not many of you do as well.

I find that straight motor oil will usually result in more engine noise on cold start up (-20* and colder). This goes for all my GM's and my oddball Civic as well. Lucas additive is generally the better additive for reducing valve train noise with a slight reduction in oil consumption. It's not gonna fix an oil burner, but it will keep it sounding smoother and protect better.

Some will call BS, but I live in the arctic circle, with many high mileage engines. They get put through their paces and some don't even get plugged in for times when it's -60*. Thinner, straight motor oils were the noisiest and thicker oils with a simple additive was, counter-intuitively, the best for healthier cold start ups and oil use.

Whether the noise is a sign of any harm being done can be debated. I don't think it's anything bad, but it doesn't sound good and I'd rather simple peace of mind of hearing nothing. Even after hundreds of thousands of kilometres on every car/truck I have and none have given me a full failure. I've killed everything but any of my engines, including my 2.0 88 Cavalier, which I could not kill.