I read the factory recommends 15w-40 but many on the forums recommend the 5w-40 instead. I read the thinner oil is better for stiction and cold weather start up but is it adequate protection when it gets warmer?

 

I've been running 15-40 for years with no probs, then I took the FTE help on oil now I run a rottella syn 5-40 and the Injects are likeing that. OEM filters.I do see a little higher oil temp when pulling but I dont think thats the oil doing it. its the other Internal word (dont make me say it) I'll just say its plugging

 

5w40 will provide similar (enough for automobile applications at least) protection to 15w40 when at temperature. Automobile XwX oils are multigrade, meaning that they can provide the same protection as essentially all of the grades between their range. This is a gross oversimplification, but you can get the full explanation at wikipedia if you want : http://en.wikipedia.org/wiki/Motor_oil.

FWIW, I prefer the Rotella, and since I currently live in a higher temp climate I just stick with the 15w40 that is cheaply and readily available at WallyWorld.

 

I use T6 5W-40 all year. It works well. It will be just fine in the heat.

 

Actually, since the 5W40 T6 is fully synthetic it has a far higher tolerance to high heat than the 15W40 will have, since 15W40 is non-synthetic usually. You can run a high quality synthetic oil about 50 degrees hotter than a non-synthetic oil, even if we don't see those temperatures in the 6.0.

Brian

 

I run 10w30 pretty much all year long. Unless I know I am going to be doing some real heavy towing I would switch to 15w40 otherwise I stick with 10w30. I run all motorcraft as well.

 

You'll get as many opinions as there are folks on the forum on the topic of oil

I don't think there's much benefit to synthetic unless you are running in cold climates or are doing oil analysis and are extending your OCIs to get the value out of the more expensive oil.

I've done some recent research, and if you want to get sort of lost in the subject, go check out the website bobistheoilguy -- you'll learn more than you can imagine. Anyway I've been running 15w 40 and after reading over on BITOG and here on FTE it seems the 6.0s will be happy on a good 10w 30 HDEO (Heavy Duty Engine Oil). So I'm going to switch to that for the foreseeable future.

Some common thinking is that the 6.0 is so hard on oil in the shearing of viscosity improvers (little polymer strands that make the oil flow slower when hot, hence the second number, the first being the oil's base weight), that if you feed it a 15w 40, it'll shear it down to a 15w 30 pretty quick, so why not feed it that to begin with.

I'm not a big rotella fan, but that's just me from stuff I've read -- like I say you'll get lots of opinions. But if you happen to like it or don't care, They also make a T5 semi-synthetic that's a 10w 40...

A friend of mine that used to design oil additive packages often told me to run an acceptable oil with the smallest delta between the base weight and the hot weight, 'cause VIs do nothing to lubricate your motor...

Clean oil and racor or motorcraft filters will do more than a lot of other things will for your 6.0.

My $.02 worth...

 

Anybody ever notice a difference in their deltas by switching oil weights or brands? I have always ran Delo 400LE 15w-40 and it seems alright.

 

A dino oil starts as the cold viscosity and uses viscosity improvers to "thicken" it up as it heats. So you'll have a 15 weight oil that acts like a 40 when it's hot.

Synthetic oil is the hot weight and uses viscosity improvers to achieve the cold weight... hence you'll have a 40 weight that behaves like a 5 weight when cold.

That's why a dino can experience shearing whereas a synthetic will not. The shearing destroys the VI of the hot weight, a synthetic doesn't experience that.

As for myself I use all of it. 5W40, 10W30 and 15W40. Overall I think 10W30 is the best compromise on price and durability.

I am really looking forward to Rotella's new CJ4 0W40, hopefullt this coming winter to those of us South of the Canada border.

Josh

 

Even though my 6.0 has some kind of valve train damage, I just switched to Rotella T5 10-30wt and added Archoil 9100 and did the 10K resistor FICM mod. Man what a difference it makes at start up, almost instant like my Triton 5.4L. I'm betting most of the improvement is from the FICM mod though.

 

i'm a converted believer in 5w40 T6 fully synthetic from shell rotella. tat oil always my baby purrs....... roar?

 

sorry, i meant to say "tat oil always makes my baby purrs". lol. must be something in my worm juice.

 

You know Josh, it just sux to get old. And worse to have old data floating in your head...

 

I would sure like to see the source substantiating this perspective.

One thing that stands out is that there is plenty of shearing in synthetic oil.

Now, maybe Rotella T6 and Mobil 1 TDT oil don't qualify in your definition of synthetic oils (I agree that they are making the synthetic claim based on the fact that severely hydrocracked oils can now claim to be "fully synthetic"). But - even Schaeffer and Amsoil, who claim to be REAL synthetics, experience shearing - at least in our 6.0L's.

 

It's called bobistheoilguy.com for starters.

Start reading in the Motor Oil University.

Josh