Rotella T5 not what it used to be?

[racin4ds]

Hi guys, I have an interesting story for you all...

First let me say I've always been a huge Rotella fan and I have service records to prove it was put in my 05 6.0 PSD the day it rolled off the lot.

As many of you know, the infamous 6.0 PSD is very hard on oil with its HEUI injection system using a HPOP. Oil temps are critical in these trucks and so is oil quality.

Any way, I have a friend who owns 3 of these trucks, all work trucks with high mileage. I've recently began doing the maintenance on them for him in exchange for work (hes a farrier). I talked him into switching to Rotella 10W30 over the Motorcraft 15W40 he's ran forever. Long story short, he calls me the other day and tells me his oil temps are 10-20* higher on average! He closely monitors his vitals and drives this particular truck a LOT so he certainly knows the average range of temp.

Temps here in Central Florida haven't changed much, 90 and Humid as heck every day. He carries the same load on the truck all the time.

He dumped the Rotella and went back to Motorcraft and calls me to tell me the temps are right back where they were!

have any of you guys seen anything similar to this? How is it even possible??? I'm about to dump my Rotella and try some just to see for myself!

 

[FCD]

I woold try T4 or T5 15W-40 and see what happens.

 

[hatt]

Why were you trying to talk him into 10w-30 for 10+ year old trucks that are known to have issues?

 

[zrxkawboy]

I agree that it probably has more to do with the weight than the brand.

 

[andyd]

What was your reasoning to go with a thinner oil at the height of the FL summer?

 

[Snagglefoot]

We do know that oil temps are also heavily dependant on RPM. Is it possible that there was less friction in the motor and somehow that caused the transmission to allow a slightly higher rpm prior to shift points?

In any case I would go with what ran at a lower temp. Veryinteresting data. Thanks for sharing it.

 

[bullwinkle]

That's interesting, that's the exact opposite of what I would expect-a 30 weight should have less friction than a 40 weight, so the oil temperatures should be lower than a 30. Of course, the PSD tends to shear 40 weight into a 30 anyway, so it probably doesn't matter!

 

[Zee09]

When people are set in their ways it tends to be suicide if you change anything.
He probably would complain if you fibbed and used his oil even.
I never talk anybody into anything. It always goes wrong.

 

[clinebarger]

Try some Mobil Delvac 1 5W-40......LOL!

 

[Lolvoguy]

fascinating

 

[Lolvoguy]

Originally Posted By: andyd
What was your reasoning to go with a thinner oil at the height of the FL summer?


I agree. Seems silly to run a THINNER oil in summer heat and expect it to protect as well as a thicker oil.
OP should recommend 0w16 next time.

 

[dnewton3]

question 1)
What "temps" are we talking about here? Coolant temps? Oil temps?
question 2)
Where's the data; the proof? Under what reasonably controlled experiment did this take place?


I find it unlikely that a grade thinner will cause temps to rise by 10 degF. Very unlikely. What's the logic here? That somehow 30 grade is so thin that friction is driven up by some horrid factor and causing heavy wear to generate additional thermal stress? I call Bovine Manure on this claim. It's impossible to believe that the 30 grade would generate so much extra friction in the engine that it would cause a 10 degF spike (oil or coolant), and yet we see LOTS of evidence that 10w-30 proves out to have perfectly normal wear rates, right along with 15w-40 in the 6.0L. Additionally, the thinner grade will pump easier; less viscosity means less resistance to flow. Less resistance means less energy needed to overcome the parasitic drag at the low and high pressure oil pumps.

The 6.0L engines have proven to run very well on 10w-30, even under heavy loads. Wear data does not lie, and is objective rather than subjective. Show me proof that the thicker grade makes and engine run 10 degF cooler, because I don't believe it. It's way more likely to be a ruse or uncontrolled factors affecting this experimental claim.

 

[beanoil]

Nope. Your friend is gaming you and wanted Motorcraft oil back in.
Changing to a 30 weight in a 6.0 is NOT going to raise temps, not 10 degrees, not 20, not 1.
Baloney.
Anything that happens to this truck from this point on will be your fault as well.

 

[jstutz]

The only reasonable thing i can think of is that it is a function of the oil viscosity and not the particular oil. The increase in oil temp sounds very high. I have read some information stating that thinner oils conduct heat better than heavier oils. If this is the case then the oil , also being heat sink, would absorb more of the heat from the engine. This would lead to cooler metal parts with hotter oil temps. Maybe talking out my butt but this is the only thing that I could come up with. The 10-20 degrees sounds crazy though.

 

[racin4ds]

Ok, I'm NOT a thin oil guy whatsoever, especially not in my diesels but my personal 05 PSD LOVES the 10W30 oil. I switched to it awhile back and found easier starting, smoother running, better MPG's etc. After reading on here how quickly the 6.0 shears a 40wt oil to a 30 anyway, it only made sense. That is why I suggested he run the 10W30.

He may be pulling my leg, I don't think he would, very honest fella, been our Farrier for awhile.

He uses an SCT monitor and closely watches all the critical parameters through the OBD port. As many of you know, ECT (coolant temp) and oil temp are watched very closely on these trucks and delta is constantly monitored to indicate oil cooler/EGR cooler failure.

I don't see how that drastic of a change is possible either, thats why I threw it on here to see if any of you guys had ever experienced the same phenomenon.