Is there a thread about engine wear using 5W-20 etc.?

Any threads regarding engine wear using 5W-20 or lower engine oil vs say 5W-30? I've never been able to find info regarding this, other than using the lighter oil is to help meet gas mileage requirements. Only seen one place where it was said engine life is about a third less. Forget the terminology, sorry. CAFE? My computer can only do one thing at a time.
Duane

 

The viscosity difference is *very* minimal.
Compared to a conventional 5w30, a synthetic 0w20 will yield LESS wear. In fact, after a few hundred km of running, a synthetic 0w20 will probably even have a higher viscosity than a conventional 5w30.

 

I'd done a little research a few years ago when I got my 07 Civic new. What little I could find mentioned most oils lost viscosity (got thicker) over time. I need to do a oil analysis sometime on the Civic's Mobil 1 5W-30 and see what the metals in it show. Around 70,000 miles now. I could only see one source online that mentioned about 30% more wear using the thinner oil. Just can't find any studies.
Duane

 

Uhm, well you definitely have *something* backwards there, because viscosity *is* "thickness". Well sort-of. Its a bit more complicated, which is why it has a separate word. But basically think of it like this; the number... 20, 30, 40, etc., is the number that represents the viscosity. The higher the number, the MORE viscous the oil is. As the number gets higher, the fluid has a greater resistance to flowing.

https://en.wikipedia.org/wiki/Viscosity

So I'll give you a bit of an explanation about the *reasons* why an oil loses viscosity;
An obvious one, can be fuel dilution. It isn't a very big one though, unless there is something really wrong with the engine. Not much worth worrying about. The *big* one, is because we use multi-viscosity oils. I.e. 0w20 rather than SAE20, which can also be expressed as 20w20. Multi-viscosity oils are typically made by adding a polymer called a "Viscosity Index Improver" to a single viscosity oil. As the oil warms out, these polymers *stretch out*, thus *increasing* the viscosity. Cooling down causes the opposite. So the two numbers; 0w: the viscosity when *cold*, 20: the viscosity at operating temperature. Means that when the oil is cold, it has the characteristics of an SAE0 oil at the same temperature. As the oil warms up, the polymers stretch out so that at operating temperature, it has a viscosity equal to that of an SAE20 at the same operating temperature.

As the oil "wears", the polymers break down. This means that the operating temperature viscosity drops (thinner), BUT, the cold viscosity remains constant.

 

That's about what my old boss (Chevron Jobber) said about the two numbers showing oil weight. Thicker oil is what I meant by a higher viscosity.
Duane