My last oil change was at 17,000 miles on my oil. It at about 13,000 miles in this change & still running strong.
No, I'm not crazy. It was just time. My father did the oil purchasing for a rock quary where he was an officer of the company and an civil engineer. For quite a number of years, they had instituted an oil sampling program to catch early problems with the off road equipment. Since they had the program up and running, they also sampled the company cars as well. Since the diesel engines in our trucks are a bit pricy to replace (about $8k for a long block installed) he suggested I may want to do the same. I ended up using OilGuard:
http://www.oilguard.com/
It costs me $8 per sample (plus $1.06 for mailing the sample). I am building up a history of the operating condition of my engine. I also sample the transmission and rear end. The advantages are:
If a problem begins to occur during the warranty period (but doesn't BREAK until after warranty) I have the ability to bring to the dealer/manufacturer evidence before the warranty is up. Second, when I sell, I have some proof about the condition of my truck from the inside. My Ford diesel mechanic is enthusiastic about what I'm doing. I have been working closely with him the entire time. Not surprisingly, I'm the only customer they have that is doing this.
The next advantage is the sampling can tell me when I NEED to change my oil. A way to extend the oil drain times is a bypass filter (also from OilGuard). It removes the smaller particles that the OEM filter leaves in the oil that accellerate internal engine wear. It removes moisture that results in the formation of acids that use up the additive package.
Oil change extention works well with the Ford 7.3 power stroke. However, the new 6.0 power stroke shears the oil enough that it appears that extended oil change intervals are not as feasable. Shearing the oil changes the viscosity enough that it needs to be changed closer to the 4-5k mile interval.
Having a Ford, I haven't followed how well the Dodge and Chevy/GMC engines do with it. A little web searching would likely give you some opinions.
I did a lot of searching before I did this and read a lot of oil industry publications on the subject, how to read the results, as well as publications by big industry on the benefits. BTW: This was all developed by the rail road industry to protect the diesel locomotives.
It is very common in big industry. For a gas engine that costs $2k to replace, it is perhaps not a big deal. A pickup engine that is $8k to replace, (and 15 quarts of oil/pop with oil prices rising) is a different matter in my NSHO...
BTW: Once nice thing about OilGuard is the results are published on a web page. A nice feature for someone who moves around a lot.
Eric