Originally Posted By: Gokhan
Why did you put 0W-40 in a Toyota? It's too thick for it.
No, it probably isn't.
Originally Posted By: L_Sludger
Follow the oil cap for your viscosity. I bet a thousand dollars that 0w40 is not specified.
Is this engine also used in other models, which are sold in other countries? If so, then wx-40 might well be allowed ouside of CAFE-area.
Apart from that, it may well be possible that a 0w-40 may be "thicker" at start-up than a 5w-30. It may also be the other way round. Take a "thin" 0w-40 and a "thick" A3/B4, and you won't find much difference. With very cold temperatures, the 0w-40 will win. Now take a more stout 0w-40 like perhaps the Rowe, compare against thin ILSAC 5w-30, and at startup temperatures the 0w-40 may have the higher viscosity. In any case, the difference in cold-start viscosity between them should be smaller than what the differences in viscosity due to a slight change in weather conditions.
Were it the viscosity of the 0w-40 to cause start-up rattle, then I'd bet at least half a crate of beer that te OP would experience a start-up rattle with the 5w-30, too, should outside temperatures just drop a few degrees.
Conclusio: there is probably a different reason. Weather change, faulty ADBV on the new filter, or perhaps some dirt came loose, somehow managed to get around the bypass valve and restricts oil flow to one of the hydraulic tappets, or whatever.