Ive always used Synthetic, in my class 8 tractor Freightliner with Detroit and my F450, 6.7 and my old F350 6.0L The 6.0 had just over 300,00miles when I traded it in, and still running strong on a local ranch, Two reasons Synthetic does not break down as fast, confirmed by oil samples, the other reason, ITS NOT FOSSIL OIL so I'm not paying "Big Oil" I give them enough with all the fuel I use. As previously stated, it kind of depends what your using your truck for, mine are over the road hot shots, and yes I pull heavy quite often, I know guys who use conventional oils, they claim a cost savings, but using a good oil sample I run mine longer therefore less oil changes, (less time in the shop for oil change) I could install a bypass oil system and run even longer, but sometimes I like to come home for a day off to get my oil changed. Run what your comfortable with..its your truck, your money. I guess you could strattle the fence and go semi synthetic like we put in the gassers.

 

I use conventional in my Kenworth with a cat c15. The company I am leased on with buys their oil in bulk and I can get Mobil delvac for $8.95 per gallon. I get my filters at a 50% discount through them too, so both fuel filters, oil filter and 10 gallons of oil only costs me $112. Synthetic oil alone would cost twice that much.

I use synthetic in my super duty, but that is 7 quarts once a year instead of 10 gallons every other month.

 

Unless I am missing something here, my TBN # is good

 

This does scare me a little now though & maybe I should just change the damn OIL once a year even if I don't hit 5,000 miles just to be safe. I thought I was doing the right thing by having the oil tested & listening to them as far as extending the changes

You guys really got me thinking now, good timing though as my next 1 year mark is in about 1 month

 

This is my basic philosophy on engine oil:
You'll never end up with regrets down the road that you over-changed your engine oil. Its not a marathon race.


I know the diesel service is more expensive and we all like to save what we can, but in my 6.2 gasser I run Penzoil Platinum and change it when the OCI reads around 40%. I don't bother with analysis because the testing costs half the price of my oil change.

 

Not to criticize anyone's opinion on time vs mileage, or synthetic vs conventional oil, but really anyone who considers these issues is ultimately taking good care of their vehicle.
With my 7qt gas truck I use full synthetic, changed once a year (about 10k miles).

 

I switched from conventional oil to Rotella T6 full synthetic. I couldn't believe the HUGE difference it made just with my cold starts every morning living here in the Northeast!

 

What weights are you using? The diesel supplement recommends certain weights for different temperatures.
Where I am, its not uncommon for the temp to go down to -15 to -20C for a month in the winter. In summer it can range from 10 to 30C
Looks like the 5w40 is a good choice for that temp range?

Would you still use 5w40 in summer hauling a 14k fifth wheel? or go lighter?

 

Welcome to the site! I'm using 5w40 all year long..

 

Only -20C? Southerner...

 

Well if your getting a UOA report look at the wear rates on the report and not just the TBN. All that scenario is illustrating that TBN isn't the end all be all of oil analysis metrics. In the days of ULSD, wear rates are more important than TBN IMHO.

A 5w40 should be fine... a 10w30 should be fine as well. -4F isn't that cold, I ran T5 in my 7.3 below zero and it started great.

 

lol that probably should have been months... but yes, southern Canada. We have had -40C and lower but usually only lasts a couple of days. the rest of the winter is usually high teens.

I'll use the 5w40 until the engine is broken in then switch to synthetic.

 

Who makes a 5w40 dino oil? I've never seen one that's not fully synthetic, but I don't often travel to Canada either.

 

Well look at that... Just learned something new. I was unaware 5w40 was only synthetic.

I'm not sure what will come in the new truck, but I'll revise my statement to say I'll be switching to synthetic after the first oil change lol

 

I believe that's because conventional base stocks require too many viscosity improves when you have such a high increase in viscosity. Going from a 5 weight to a 40 weight without shearing down right away isn't easy!