ppcpilot

Been looking around, reading up on this...

W=Winter, or cold viscosity, correct? Thin is good at startup, correct?

Why in the world would anyone NOT want to use 0w-30 vs 5w-30?

Does the 0w, although getting to parts faster, not provide enough lube vs the 5w?

I keep getting scared about putting the GC 0w-30 in the RX vs some other 'synthetic' 5w-30 as recommended by Lexus. My manual also says 10w30 is ok if your temps don't get below 10degrees (which in south louisiana, doesn't ever happen.

Only thing I can figure, is that supposedly there is less shearing if you compare by the book standards SAE 30, vs 10w30, vs 5w30, vs0w30. Textbook, your oil would 'break down faster' if you used a 0w30 vs 10w30, the tradeoff being you could use your car in cold cold temps.

Does Castrol 0w30 break the rules in the shearing dept? Does it actually not shear down faster/more than say 5w30?

I just want the longest life out of my RX as I can get.

TunedRX300

SAE weight is a range. German Castrol viscosity is 12 cSt, thicker than most 5w-30 oil. See thin oil myth link
http://theoildrop.server101.com/foru...e=0#Post711581

ppcpilot

Ah. Ok..so the only time a 0w-30 would be 'thin' would be at extremely cold temps, when you need it to be thin..at 'room temp', a 0w-30 and 5w-30 should be about the same thickness. In conventional oils, given all else is equal, in a south louisiana environment, you would want to go with a 10w-30 because the temp never gets below 10 degrees, and there are less viscosity improvers, which means less shearing of the 'hot' viscosity over time vs a 5 or 0w-30.

With the synthetics, all bets are off, as they don't require VIs to have the wide range of operating temps. This would be why Castrol's only full PAO synthetic is a 0w-30 and they don't offer it in other 30wts...it won't shear or it won't shear as much as a conventional 0w-30 should over time.

Do I have it right? Do I pass Oil 101?

TunedRX300

You have been reading up on oil
SAE requies a "0w" weight to have a MAX viscosity of 6200 cP @ -35c. That viscosity won't be reached with mineral oil easily, even for highly refined Group III base oil. That is why GC needs to be PAO based and cheaper "fake" synthetic are mostly 5w weights.

The common misconception is one needs only the better flow of synthetic oil at the extremely cold temperature. But the ideal viscosity for ANY temperature is 10 cSt. In fact, no motor oil is too thin at room temperature.

Take a look at M1 5w-30, at 40 degree C it is 64.8 cSt http://www.mobil1.com/USA-English/Lu...bil1_5W-30.asp
M1 0w-30 is a little better 63.1 cSt, still too thick for lubricating engine parts, but better than 5w-30
http://www.mobil.com/USA-English/Lub...bil1_0W-30.asp

Now 40 degree C is over 100 degree F, no one is starting his car everyday at that temperature. More reasonable summer temperature is 60-70 degree F, but the difference is multiple magnitude larger than that 1.7 cSt difference at 40 degree C. Because the difference is non-linear: as temperature drops, the viscosity difference increases multiple magnitude higher.
Why does one care? Next time you drive the RX in the morning, time how long it reaches operating temperature, that is how long the engine has been operating with oil too thick for optimum lubrication. With synthetic oil, the oil pump will not work as hard, flow to critical parts of the engines are closer to 10 cSt, and you get slightly better mpg.
It is up to you to believe pure synthetic oil are needed. Most people could care less, at long as the car fire up.