Ruralmedic

FWIW, my latest used oil analysis report from Blackstone Labs. Schaeffer's Supreme 7000 15W-40

Miles on oil: 14,301
Mile on engine: 139,276
Filter: Fleetguard StrataPore LF3894
Air filter: Fleetguard BHAF w/Outerwears water repellant pre-filter
Use: March-Sept. '05

Elements in ppm:
Aluminum 2
Chromium 1
Iron 16
Copper 2
Tin 1
Moly 78
Boron 6
Silicon 3
Calcium 3106
Magnesium 42
Phosphorus 1021
Zinc 1235

SUS viscosity@212F 78.3(SAE 40 grade)
Flashpoint 425F
Fuel <0.5%
Insolubles 0.4%
Total Base Number 8.3

This oil is a semi-synthetic, contains 20-25% PAO basestock, the rest is group II+ petroleum and an excellant additive package. It's designed for extended drain service, and according to this I could have gone with it longer. Cost was less than $12 a gallon delivered. I changed it out and running their full synthetic 5W-40 for the tundra winter.

Also, used up to 50% blend of bio-diesel fuel during this change interval.

smokindog

I have been sending my oil to Blackstone since my truck was new. I regularly change my oil at 15K mile intervals. I have customers with fleets of 15-500 trucks and not one of them ever drops oil before 25K miles. Granted the big trucks have 10+ gallon capacity, but it's relevant to the size of the engine. I've never understood why certain fellas feel they are doing something better for their units by changing at 3K mile or even 7K mile intervals. Just because the oil changes color doesn't mean it loses its lubrication properties. The lube manufacturers like when you replace more often, but ask any of their technical support guys and they will tell you that it doesn't make a difference.

infidel

My feeling and oil analysis experience is that good quality dino oil in a Cummins can easily go 10k before changing. Oil quality has changed immensely since the service intervals were written even for engines just a couple years old.
Total waste of money, time and natural resources to be changing at 3 or 5k.