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But if a 5w40 is better than a 5w30... then isnt a 5w50 better than both?

I thank everyone for their info... I am now MORE confused... So the number before the W in no way reflects how thick the oil is at room temp???? I understand that the rating is based on flow at -30 degrees to meet the definition of the rating. But how would that inherent viscosity at -30 NOT...

Per Castrols website... The low temperature viscosity of the oil is a measurement that simulates starting a car on a cold winter day. That value has the letter “W” after the number and has a dash after the W. For example, if the oil is a 5W-30, the 5W part describes the viscosity of the oil at...

Hypothetically, if an older engine has .003 bearing clearance, and new was .001, why wouldn't a higher viscosity oil fill the gap better and lower wear? We have all heard of car salesman throwing in very thick oils or honey goop to quiet rod knock just to sell a car... It does affect the rod...

That makes sense. Just watched some video's. I think the curve explains some of what I was asking... So when an engine is starting, its in "Dry Friction." Surface irregularities on the bearing need to be compensated for by the oil thickness as hydrostatic pressure hasnt kicked in. At higher RPM...

When we took our CRV to the dealer, AFTER the warranty ran out, they suggested going to a 5w20 due to possible fuel dilution issues. I thought Europe used 5w20 as their default? Not sure.

Wouldn't a high mileage older car have greater bearing clearances than new? Even though its not being raced, wouldnt a thicker oil have a benefit?

My error, Toyota never officially recommended this. Looks like there is plenty of discussion on the internet that in Europe they use the thicker oil as thats what recommended, but here, due to MPG/regulations, thinner oils are specc'd... No?

Question... A thinner oil flows faster, so gets to the bearings faster... But a thick oil "clings better" so its already there on start up? I thought that was one of the reasons toyota starting recommending 5w over 0w oils? To clarify my question, I am interested in what can be done to keep...

Not sure I understand your reply? So a 50w is better, or not? Toyota initially spec's 0w20, then with increasing bearing failures went to a 5w20 Honda had bearing issues in the CRV (fuel dilution), and then recommended a thicker oil, and eventually increased the motor running temps... As cars...

Ive read tons of threads on here, and still don't get it... For any given car, the owners manual spec's possible oil grades... Lets take the Mercedes m113 engine for example (used from 2002-2014 or so)... Mercedes specs that you can use anywhere from a 0-30W, to a 20w50 in the owners manual...