Anyone switch form 15w40 to 10w30 in 12.7 Detroit’s?

I wouldn't change oil weights and viscosity between inframe/overhauls, I've always been told not to. Why are you wanting to switch?

 

Friction changes in engine oil is meaningless.

What you do need to do is use the rated oil for a particular engine. Any other oils might cause the destruction of same. That's like putting water into your blood vessal system because it flows better than your blood. You wont be liking it too long because then you be dead.

 

It may work. But if engine is not just been rebuilt I would not do it. Any full synthetic oil will most likely weep past al gasket seals.

 

but you will be on cloud 9 until then.

 

Has your current oil let you down in any way? You probably won't realize a significant increase in fuel economy, whereas a company with 100+ trucks might.

It's good to think about these things. It's possible that there are other ways you can increase your revenue without possibly jeopardizing the heart of your bread and butter.

 

To add a little perspective: The megas get away with 50K oil changes using standard 15-40 for 350K - 450K miles and the truck's engine is still usually very serviceable.

 

I have gone from 10 to 20 k in the last 22 yrs. In long haul operation . 50 k sounds crazy I know they change filters and monitor oil . Oil has improved and Diesel no longer has a lot of sulfur . Same with cars no lead means engine runs cleaner. I think the lighter oil would burn or blow by rings or through seals easier. A lot of people swear by Motorcote to accomplish what you want. Never tried it myself. Tried slick 50 once on an old Cat trying to increase mpg. All I got was a leaking rear main seal that stopped when I got rid of the snake oil.