Quote:
Originally Posted by The Master Cylinder
15w40 is only "thin" when the oil is cold which is a good thing because it flows to the bearings faster at start up. 15w40 oil doesn't stay at 15 when the engine warms up. When the engine is at operating temperature it is 40.
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No harm meant , I know that with multi viscosity oils that the only time that the low number is used is when the oil is cold . Thin oil flows quicker .Usually a cold engine will have more clearance than a hot engine and can be subject to knocks at start up . It doesn't get very cold where I live . I would prefer 20W for cold flow here .. Quick flow isn't the only thing that is important . I feel that more viscosity to a point will better cushion the bearings . The owners manual recommends 20W in winter and 40W in summer . 20W 40 would be ideal . I feel that 50w would be good for older engines with some wear . I feel that most engines over 85 years old will have some wear unless they have been rebuilt recently . I use 20W50 and it seems to work well for me .