Originally Posted by djb383 (Post 945978)

Ok......if you're positive......'cause the 15W40 is plain ol' thick conventional motor oil, while the 5W40 is synthetic.

Originally Posted by FrankZ (Post 945994)

This link will explain why Zinc is important in a new motor.
http://www.hotrod.com/techarticles/e...l_summary.html

As I stated earlier, if the motor has already been run or has any miles on it at all, there's simply no need to use a high zinc content oil. Either the damage is already done or thr the lifters and cam are already broken in and will not benefit enough from the zinc in the oil.

Run a conventional oil, a Conventional-Synthetic blend, or straight synthetic if you like.

Originally Posted by ACCoffroad (Post 945987)

Alright buddy you gonna help me out or be critical of my thread? everybody else is being helpful here bro. i realize 15w40 is plain old DIESEL oil thats fine thats why i asked before i went out and bought 6 quarts

Originally Posted by s14unimog (Post 945917)

I don't think you actually need something that heavy but I will say I bet you'll see some cooler operating temperatures. I use the Valvolines equivalent in my 500hp turbo 4cyl. but that's a different story obviously. I don't see why you NEED to go to it. If you're wanting something heavier just use a 40 weight. Regionally, where are you located?

Originally Posted by djb383 (Post 946006)

Sorry, didn't mean to bunch up any panties. Here's some good reading http://www.bobistheoilguy.com/cms/in...d=84&Itemid=92. Afterwards, u may ask yourself, why would I use 15W40 in anything other than a lawnmower or a Harley. LOL

Originally Posted by ACCoffroad (Post 945997)

So i can go straight to a synthetic? No flushing or anything? Dumb question? hahaha :rofl:

Originally Posted by SamSissine2 (Post 946007)

I may be wrong but wouldn't a thicker oil cause increased temps and not lower temps since there is a higher fluid friction??

Originally Posted by FrankZ (Post 946000)

Drain the pan, replace the filter, fill it up with whatever you want.....run it.

Originally Posted by ACCoffroad (Post 946010)

No problem man, ive read some stuff on that website as well. Yea when i first saw 15w40 i thought it was a joke but theres alot of guys running it, i dont think ill be one though.

Originally Posted by djb383 (Post 946030)

I'm not talking about BITOG.......read the papers written by Dr. A.E. Haas starting with Motor Oil 101.

Originally Posted by prerunner1982 (Post 946051)

I have been running the Rotella T 15w40 for awhile now and have not noticed any harm to my engine yet. During the winter months I might switch to a lighter weight Valvaline, but typically in the summer time I will run the Rotella.

I have also read that the zinc is better for the flat tappet 4.0 liter.

Even if the extra Zinc is not needed, the Rotella is usually a bit cheaper..