Thank you for the explanation. My understanding was a viscosity at a higher level, its not as prone to thinning and overall thickness conventional motor oil has, which wouldnt you want a higher viscosity oil in terms of performace, where as lower viscosity numbers are thinner, running hotter. So Using average motor oil can technically lose viscosity quicker, because it’s thinner and will wear quicker. Where is if you use a synthetic-based, it’s more protective In protecting engine parts, and then it less susceptible to thinning at higher/extreme temperatures.
Sorry, but I'm having a really tough time even understanding what you're saying here.
All engine oils are prone to sheering, which, for lack of a better term, is where the oil is mechanical ripped apart by the extreme pressure and heat at certain places(namely the bearings and cam lobes). This phenomenon does reduce the viscosity of the oil. As technology has improved, oils have become more resistant to this, although as a rule of thumb the wider the viscosity spread the more prone it is to happening.
Still, any group III oil is good and perfectly safe for a modern engine unless you're just all out hammering on it. If you are, there are specialty oils for that application. You probably won't find them on the shelf at your favorite auto parts store either as they tend to not be suitable for street use(the "real" Valvoline VR-1 racing oil is one such oil-it's loaded with ZDDP and other anti-wear additives, but is very low in detergent content. It's what the doctor ordered for running pedal to the floor for a few hours since it gives protection in those extreme conditions and the lack of detergent keeps it from foaming, but you'd better not leave it in your sump very long unless you want to deal with all the crud it doesn't keep in suspension).
BTW, Ford specs 5W-20 for a lot of their passenger cars now for CAFE reasons. I run 5W-30(Mobil 1 usually) for better wear protection at the loss of a couple of tenths of a mile per gallon. That's a personal decision and not something I'd advocate everyone doing-when in doubt stick with what the manufacturer says, although 5W-30 is an approved "alternate" grade for my car.
Also, I think you might have a misunderstanding of how multi-grade oils work.
Let's take a monograde oil(aka "straight weight") like SAE 30. It is a general rule for any fluid that viscosity is inversely proportional to temperature-i.e. fluids are most viscous at lower temperatures and least viscous at higher temperatures. This is something you know intuitively-look at how easy it is to pour hot and cold syrup, for example.
If you were to graph the viscosity vs. temperature for something like SAE 30, you see a relatively linear decrease in viscosity with increasing ambient temperatures, or at least linear over the course of typical ambient temperatures up to engine operating temperatures. This CAN be a bad thing if you're at very low ambient temperatures, as the oil is very viscous at low temperatures, although it works fine at engine operating temperatures.
Multi-grade oils employ some special magic
. Basically, what they do is at typical non-running ambient temperatures-say somewhere in the range of 0-100ºF-they have a viscosity profile similar to a straight weight oil of the lower number marked on the bottle. At engine operating temperature-say in the 180-200ºF range-their viscosity profile is more like that of the higher weight marked on the bottle.
The end result is that multi-grade oils have a somewhat more "flat" viscosity vs. temperature curve than a straight weight oil. The net result of that is generally a good thing, especially if you live somewhere that actually has some semblance of 4 seasons, as you're putting a lot less strain on the starter, oil pump, crankshaft, and pretty much every other part when starting the engine. You're also making the sure that the oil gets where it needs to go a lot more easily. At the same time, the oil holds its viscosity at operating temperature so that you can maintain effective boundary protection.
