"Oil Change Intervals - Why Try To Extend?"
For the simple reason that it's a wast of time and money not to. Today's modern vehicles are not your fathers 55 Chevy with a inline straight 6 engine and 3 on the tree. Today's modern engines, transmissions and other drivetrain components are held to much tighter tollerences then components of old. Cleaner running, more efficient and produce less contaminat byproducts. On the flip side today's modern engine, gear / transmission fluids and greases are also a vast improvement over older lubricants.
I run TRC's Moly XL Pro-Spec in all my engines. 5W30 in all gas engines and 15W/40 in the diesels.
1997 Ford E450 18 foot cube van w/7.3L Powerstroke. Average OCI 24,000 miles
1996 Ford F150 pickup truck w/V6 gas engine. Average OCI 11,000 miles.
1988 Chevrolet G30 12 foot cube van w/V8 gas engine. Average OCI 9,000 miles.
2001 Freightliner FL112 tractor w/C12 Caterpillar engine. Average OCI 33,000 miles.
1998 International 4900 straight truck w/DT530E engine. Average OCI 29,000 miles.
2001 Chevrolet Impala w/V6 gas engine. Average OCI 11,000 miles.
This is just a small sampling of my fleet.
I run UOA's on all vehicles, 3,000 for gas engines and 5-10,000 for the diesels. Transmission and rear gear oils are tested at 100,000 mile intervals.
To this date I have never had a lubricant related failure. A properly run UOA program will not only extend your drain intervals but will also extend the life of the vehicle or equipment by catching possible problems before they destroy a component and take it out of service for repair.