Aug 17, 2011. #3. from shell's site; Shell Rotella® T5 is formulated and designed to energize the oil's performance and provides fueleconomy benefits*, improved low-temperature flow, and delivers an advanced "Low-SAPS" formulation which helps control the blocking or poisoning of exhaust after-treatment devices. The oil is graded based on the coldest temperature the oil is at, as SAE viscosity grade 0W, 5W, 10W, 15W, 20W, or 25W. The lower the viscosity grade, the lower the oil temperature. For example, if an oil passes specifications for 10W and 5W but fails for 0W, you must label the oil as SAE 5W. At operating temp. The two oils are very close in viscosity. Good plan to change oil early. An early change gets all the break in metal too fine for the filter to catch out of the engine. Put a magnet on your filter to trap even more break in metal. Use magnet till about 3000 miles or so. For instance, since a lighter base stock is used in the 5W formula, the lubricant may have more evaporation than a 10W or 15W. The 5W might also cost more than the 15W and break down more of the viscosity improver additives in the formula. You may also decide to use a synthetic lubricant with the same viscosity and quality claims. With temperatures going down to 20F a 10W oil will not be an issue. Should you be faced with that kind of "extreme" cold you can just let your car warm up for 30 to 60 seconds before you start rolling. There is a small benefit of using a 10W instead of a 5W oil in that the 10W will normally have less viscosity improvers in it. BsBE.

difference between 10w and 15w oil