I've also been doing a bit of investigating to learn a bit more about engine oils.
This web site talks a lot about it:http://en.wikipedia.org/wiki/Engine_oil
This one suggests that it's not a good idea to use a multigrade oil with a wide operating range, like 0W50, for example.www.uponone.com/howtos/18.pdf
The reason why is that the way they make an oil into a multigrade oil is by adding polymers called "viscosity index improvers". Basically, these are really long molecules, which coil up when they're cold, and unravel when they're warm.
When they coil up, they have less effect on the oil they're dissolved in, so the oil behaves much as it would if they weren't dissolved in it. However, when the oil warms up, these polymer molecules unravel and effectively act much like a hair clog in a drain. They impart drag on the oil molecules so that they can't move as easily, and the result is that the oil doesn't loose it's viscosity nearly as much as it otherwise would. That is, the long chain spagetti in the oil makes it artifically "thicker" at warm temperatures. But, that spaghetti coils up when cold, so as not to increase the viscosity at low temperatures.
Apparantly, the problem is that these polymers can precipitate out and cake up on the metal parts of the engine, causing things like sticking rings and valves.
The wider the temperature range you want the oil to work well over, the more polymer you have to add to suppress the natural thinning of the oil with heat, and the greater the POTENTIAL for problems.
Another great site is this one:http://minimopar.knizefamily.net/oilfilterstudy.html
The guy simply bought oil filters and cut them open to find out how well they were made. Basically, the prime selection criteria he looked at were as follows:
1. Filter element size - basically the larger the surface area of the filter, the more dirt it will catch before becoming clogged. When a filter becomes clogged, then there's a bypass valve that allows oil to flow through it unfiltered to ensure the engine at least gets some oil (albeit potentially dirty oil).
2. The kind of filter element - paper filters have larger holes than synthetic media, so they don't filter the oil as clean as synthetic media. Synthetic media also has MORE holes than paper, so even though the holes are smaller, they don't present a flow restriction. Some high performace filters have a hole size gradient in the filtration media so that the largest holes are closest to the upstream face of the filtration media and the smallest are downstream, thereby being able to catch much MORE dirt before needing replacement.
In general, most good quality oil filters use a paper filtration media between 300 and 350 square inches in size. Some oil filters have filtration elements that are 400 square inches in size.
Surprisingly, the filter company that spends the most on advertising, FRAM, spends the least on making good oil filters. The two FRAM filters tested had a paper filtration media of only 193 and 248 square inches; the lowest of all the filters he tested.
The BEST filter and best value oil filter tested turned out to be the same one; the Purolater Pure One filter with a synthetic filtration media that's a whopping 400 square inches in size for only about $5. (the "Nordic Group" web site referred to later on in this post says that a synthetic filtration media has not been shown to provide any tangible benefit over paper filtration media in oil filters)
The best inexpensive filter was the STP filter (made by Champion) with a paper filtration element that's 360 square inches in size (well above the average for inexpensive oil filters) for about $3 (which is typical for a cheap filter).
I particularily like the guy's approach. He throws away all the racing stripes emblazoned on the packaging, and cuts the filters open to see what's inside. Then, he uses good old fashioned common sense to reason that the larger the area of the filtration element, the more dirt the filter can hole, and so the longer that filter will last. We need more of that kind of horse sense in consumer advocacy, and fewer racing stripes on the manufacturer's packaging.
I think what I'm going to do is stick with 5W30 for all my oil changes. The amount of extra polymer in the oil needed to make for the wider temperature range isn't much. Also, the reason why newer cars call for thinner oil (5W30 instead of 10W30 is because engine tolerances have gotten smaller, so they need a less viscous oil that can flow through those tighter tolerances during start-up better (http://www.nordicgroup.us/oil.htm) And, I'm simply going to buy whatever motor oil I can find with an API SJ rating or higher (SL) cuz it's the sludge that forms in motor oil that's much more of a concern than metal-to-metal contact in the engine. So, according to this guy (http://www.nordicgroup.us/oil.htm), it makes a lot more sense to buy ordinary oil and change it on a regular basis to eliminate the sludge in suspension than buy premium oil (like synthetic oil) and not change it as often. The synthetic oil doesn't break down at high temperatures and flows better at low temperatures, but sludge accumulates in it just as quickly as a cheap oil. Apparantly, even though synthetic oils are better at holding sludge in suspension, they're not that much better that you can change your synthetic oil every 25,000 miles as some synthetic oil manufacturers were originally suggesting.
And, I'm going to phone around to find out who sells STP oil filters (and maybe Purolator oil filters too). I think Wal-Mart sells STP oil filters if I'm not mistaken.
I thank everyone for their time and input.