I have a 2009 Ram 2500 HD 4X4 6.7 cummins 240K miles. Book calls for 6K oil change intervals but all I do pretty much is run highway so it seems I'm changing the oil a ridiculous amount. Would it be safe to extend intervals out to 8K? I use Rotella T6 Full Synthetic oil. Thanks!
If all you do is highway speed driving that's perfectly fine. You don't get much wear when you're driving 670 miles an hour. Some guys even push it to $10,000 miles if they're doing all highway driving
Potentially, but don't forget that loss of viscosity isn't the only potential problem. You also can have oil consumption and leaks. The mistake people often make with extended oil change intervals is to not check the oil more frequently and end up running low. As long as you are checking the level often you should be fine.
