Jim,
I need to add some caveats to your statement.
First, you need to draw a line between Synthetics and Mineral oil. The Used Oil Analysis (UOA) shows most mineral oils breaking down in 3000-5000 miles depending on use and application. Synthetics in the same application will usually double the life to 6000-10,000 miles. Note that the new european cars with long change intervals specify synthetic oils.
Second, the long intervals specified by some manufactures are really pushing the limit, and exceeding it to a certain extent. There have been UOA's of BMW's running BMW Branded Synthetic (A group III+ castrol oil) for the full 15,000 mile interval, they are not pretty. The oil appears okay for about 10,000 miles.
Third, the length of time you can go between oil changes is a function of 1) oil capacity (more capacity, more additives to deplete), 2) how highly stressed the engine is, 3) engine condition, and 4) driving conditions. Short trips, cold weather, heavy towing = shorter changes, highway driving= longer changes.
Fourth, I would not recommend going the full 7500 mile interval on a mineral oil in the cruiser, I would expect 5000 to be the limit. I will be changing out the M1 0w-40 on mine at 6000 and taking an oil sample for analysis to get an idea of how long the oil should be lasting.
Finally, concerning bypass filters. I am still not sold. If any of you want, go to bobistheoilguy.com under the used oil analysis and read the discussion of the 30,000 mile oil change with a bypass. I have my concerns because I have not seen any side by side comparision testing between having a bypass and not.
The summary of the discussion on bobistheoilguy is, the guy using the bypass is draining 1-1.5 quarts every 3000 miles and changing the bypass filter (a roll of toilet paper, still strikes me as funny, but I guess it keeps your s**t clean

). So he drains and adds a quart every 3,000 and by 30,000 miles has done 2.5 oil changes in essence. My concern is that it is not the bypass filter doing the cleaning but in fact the constand draining and adding of a little oil.
I also question the economics of bypass filters. By the time you spend the $200 or so for the filter, plus the time and mess of constantly changing the filter element, why not just run the oil 6000-10,000 miles and change it out.
Cary
As always my opinion is worth the proper use of a bypass filter.
