For most oils, stay away from the wide-viscosity-range oils. In a synthetic oil not as much so, but synthetic oils are not all the same, they come from different basestocks (better = more $$) and some are actually "synthetics" from regular oil cracked enough times to be labeled as a "synthetic". Better synthetics (ex: RedLine = polyolester basestock) use better basestocks.
Mobil 1 used to be the standard, with some more expensive oils a little above them (RedLine, Amsoil, etc) and only mimimally better. Now Mobil 1 has messed around with what Mobil 1 is, undoubtably market/price pressure, and not all Mobil 1 grades are what they used to be. I still run Mobil 1 "extended drain oil"? oil in some cars, Delvac 1 in another, and Amsoil / Redline in still others depending on how much I want to keep them and how hard I run them. For the LR which is a bit of a rich/dirty engine and many say is prone to sludge production, I would use Mobil's Delvac 1 synthetic (a diesel oil, has a better additive package to make the diesel approvals but also approved for gasoline engines) for its increased ability to handle soot. Unfortunately it is available only in 15W-50 I believe, which works but IMO is not ideal. I run Amsoil Heavy Duty Diesel and Marine 10W-40 in my LR engine, works well for all temps here in Michigan (harder to find and a little more $$).
I like the 10W-30 synthetic, good protection with resonable economy. If you want slightly better economy you can go with a 5W or 0W I suppose, but I believe that they are recommended only in the NAS engine fluids in the RAVE manual, other countries' recommendations are 10W for the same climates, LR is probably using the thinner oil in the US to get better EPA economy numbers or better emission numbers, very common in the automobile business these days, ... it's all about numbers. The bean-counters run Engineering here in the auto biz these days, we engineers are the decision makers of the past.
In many oils (including some synthetics) viscosity modifiers are used to stretch the viscosity range, for example you might start with a 5weight oil and add some short-chain polymers to gain the 5W-40 ratings. This works okay, but the short-chain polymers break down quickly and in high-shear areas such as camshaft lobes or rings the polymers aren't effective so you are essentially running an oil with the protection of a 5weight oil in those areas. A bad thing. Multi-grade dino oils are a very short-term solution IMO and even low-end synthetics are much better, but still stick with the smaller ranges as a rule-of-thumb (the original Mobil 1 5W-30 for example needed no viscosity modifiers to achieve its 5W-30 rating, a very good oil).
The other part of the story is that only a few anal-retentive engineer types among us are likely to run engines long and hard, and have oil analyzed regularly to see how much longer than the truck's useful life we can make the engine run without failure, ... in which case most premium oils will work fine if changed regularly, it's probably overkill, but someone asked (again).
Is the K&N vs paper filter question next?
- Jeff Miller
. The truck still runs, what more can you ask from an engine with such mileage?