Yeah 5w-40 is quiet the spread... such a spread that the SAE allows for 0w-40, 5w-40s and 10w-40 to have a slightly lower high temp high shear rating of 3.5 compared to 3.7 minimum for 15w-40m 20w-40, 25w-40 & 40wt oils.

SAE J300 | Widman International

Wow, we haven't had a good oil battle in what, a month? Any bets as to how many pages this one runs?

Time for another page... So I've had the truck now a couple of weeks and have about 800 miles on it. The temperatures are dipping to around -4C (24F) at night. I know the oil that came in it from the factory is fine for these temps. Just wondering if, and it will come, the -20C (-4F) temps come around if I should change to synthetic. OR should I leave the factory oil in? Thinking break in period (which I know varies from anyone you ask, but I'll ask... how long is the break in period for a 6.7?). I won't be doing any heavy towing over the winter, maybe 5000lbs a couple of times a month.

I guess this is a case of break in period vs cold weather temps... will prolly put on another 1200 miles before the temps start to really drop. Do I wait or go ahead and change the oil sooner?

I have 7 vehicles to keep track of and like to keep things as simple as possible.......I adopted the practice of changing oil twice a year during daylight savings adjustments. I never come anywhere near the miles intervals and dont think the old school every 90 days is really needed for synthetic,,,of course...when my vehicles where under warranty....i did what ever the service schedule said was needed.

Lee...
Put synthetic in it and forget about it.

As far as what brand....any of the normal...
Rotella T6 blue jug stuff......Mobil 1 turbo diesel truck...

People treat oil brands like their grand daddy's shotgun ......
Watch your monitor and change when it says. If you can afford it run synthetic all the time. It's benefits are less in the summer than winter but if you can run it year round. Any of them. Get on their website ..Put your vehicle in....and get the oil they recommend.

Good luck

all im saying is that syn oil is thinner yes? if you have high mileage. beware you may blow a oil o-ring or two...thats all the syn oil did help with over all running temp... it did keep the temp lower than convent oil,but it is thinner and will blow out any weak oil o-rings under a heavy load such as a large 5th wheel mine did .....joseph

stop. See this is the problem. Please explain to all of us how you came to blame the oil on that.
Like as in there could be no effing way that was purely coincidental.
This is the the silliest argument when people say this stuff. So in other words what you are saying is your truck had components that needed replaced in the first place and synthetic brought that to the forefront??? Something like that?

Dear Lord. Good luck proving that .

The oil viscosity is exactly the same regardless of conventional or synthetic. The only difference is the makeup of the synthetic over conventional oil. I have only used full synthetic oil in all my cars and trucks and have no oil leaks from the motor. I have a car with 275,000 miles on it and not a single seal failure or gasket leak. A synthetic blend is useless because they dont say how much synthetic they mix in.

WOW, I have been using synthetic oil since 1974... in cars/trucks/motorcycles/generators/lawn tractors/lawn mowers...

I have never had a seal or "O"ring failure... even cars I have drove over 250,000 miles from NEW....

my 1983 Motorcycle from new to 155,000 miles never leaked ... or used oil...

and most had an oil change at 10,000 mile intervals., or every year...

and the weight... 5w20 is the same regardless of brand or type of oil...
same will all other weights of oil or fluid.... like 75w90 .. etc...

Education... is becoming a lost art....