Oil

I use Mobil 1 5W30 in my '02 TJ, I have since 800 miles.

CDG

It is attemting to apply a rule of thumb to one type of oil chemistry to an entirely different chemical formulation... The folklore for dinosaur urine is that the extended viscosity range is gained by adding a witches brew to a base stock derived from cracking crude oil. And that the components of this witches brew break down due to both time and load... lowering the effective viscosity range. Whereas the Mobil One synthetic is made from a different type of base stock [which may also come from dinosaur pee] of a different chemical composition entirely that needs less brewing to obtain a wide viscosity range, thus being a slightly less complicated witches brew so the different components will decay at a fairly uniform rate, so the viscosity stays stable over a longer service interval.

On this side of the pond, oil viscosity is only measured at two temperature points... so at lower temps it may thicken quickly [or may not] and at higher temps it may thin non-linearily [or may not]...making viscosity range of limited usefulness in describing much of real interest about the oil.

The synths tend to have better lube qualities at low temps and at high temps...with lower overall friction that stays a bit more constant over the service interval... and that alone may make it worth considering.

I haven't noticed any odd results of cutting a 4.0 over to synth over 2.5 years... oil consumption is extremely low and I would guess a few percentage better oil mileage particularly on longer trips. ...and I still change it rather aggressively.

Why? Is there something about a Mobil One 5w40 oil that makes it less suitable than a 5w30? Note that the original question was specifically about Mobile One, not dinopee.

I change every 3000-3500 miles, and over that time oil consumption is not discernable really.

Dave Milne, Scotland '91 Grand Wag>

I used to burn about a half quart or less in that 3-4k mile change interval, but then a miracle occurred. I finally got a round tuit and changed the rear main seal and the valve cover plus gasket and the consumption is now undetectable--go figure. Didn't really notice any difference in leakage between the dino and drugstore versions before finally fixing the leaks. Main benefit other than slight increase in mileage appears to be a bit better holding of oil pressure in triple digit desert temps and observably smoother starting on frozen winter mornings in the mountains. Haven't really changed the oil change interval much, as it gives a good excuse to crawl underneath and look for other stuff.