Questions on oil

Most any oil will need polymeric viscosity improvers to do the spread between the low number and the high number, so it all depends on what the actual base oil is. Don't want to break it all down technically, suffice to say, a 10w30 tends to be more shear stable and a 0w40, 5w40, or 15w40. There are many 10w30 synthetics that are actually a straight 30w oil, but qualify as a 10w30 because of their low cold flow properties. The point being, it takes far less VI in the oil formulation. And VI is what breaks down in an oil and can shear. And the additive package makes up 20% of any motor oil. How the add pack is formulated has as much to do with how the oil will "perform" in an engine as the oil itself.

I have a pile of used oil sample reports from many oil changes where I used 15w40, 5w40, and 10w30 all in a 2000 factory remanned Detroit Series 60 12.7L. The 10w30 performs just fine even on that old motor that is over 600,000 miles into its second life. The change in viscosity (representing shear going on with the oil) was less with the 10w30 than either the 15w40 or 5w40. Over at the BITOG website, in their used oil analysis section, there are several that have posted used oil reports of using 10w30 long term in all kinds of class 8 engines and various brands of oils.

How the numbers look on an oil sample may be "fine" to a lab, but it is the patterns between oil samples and how the numbers interrelate with each other that tell a bigger picture. A lab will tell you its fine, just because the sample still is within the limits. It's the variations that show up in comparing samples that can tell you if things really are all that "fine". Used oil analysis is as much an art form as it is a science.

All the major oils are pretty good. Nothing wrong with using a XXw40 over a XXw30, but the 30's will do a good job. Some feel that "thicker is better" and that fits in their comfort level. first off, that is a misnomer. A 40w oil is not "thicker" than a 30w oil, it just more resistant to flow. That is what viscosity is.... flow rate. Ask Isaac Newton in the next life and he will explain.

 

Thanks for the advice seems like the shop has a limited amount of different type of oil. I am looking at a Mobil Delvac 15w 40. At about $360 with fuel filter and lube job plus some other little extra work. I think trans oil check. I think i will run that for my base what do you think?

 

Well, where you run and ambient temperatures should be taken in to consideration. A 5w40 or as was mentioned, a 0w40, would be advisable if you stay in cold weather a lot and shut the engine down often. The cold flow is much better with those two oils over a 15w40 and the oil can get moving thru the engine better on a cold day start up.

You can even switch back and forth seasonally. 5w40 in the winter months and 15w40 in the warmer months. I do. I am using 5w40 right now, but use the same brand of 15w40 in the warmer months.

 

Thanks i will order a few boxes the place was limited on oils. Seem like getting your own stuff is way better then the shops stuff filters didnt seem oem or even right. No label or brand. I am considering doing it myself i dont trust these Grease Monkeys. Just wondering how hard is it. My last truck was a 379 with a c12 one huge big oil filter and one diesel filter was about my only worries. This thing has about 5 or so.

 

There are 4 fuel filters on yours. They MUST be done in a particular order to be done properly and not have any complications. I don't have a DD15, but was watching and asking about the procedure at a Mack dealership truck lube place I use on occasion. They showed me the steps they went thru and said it was critical to get it right on the DD15. I would get with a good shop that a mechanic can show you the procedure. I don't want to try and describe it here and give inaccurate information. Maybe someone else can chime in and help guide you.

 

Thanks the shops around here seem to not know how to change it. I asked one and he didnt even know these trucks can spin bearings if you change fuel and oil filters at the same time. As well i saw them use starting fluid to prime a dd15. After seeing that i was out of there. I will find a better shop. Or just learn to do it myself my truck does not run very hard. So changing the oil twice a year is what i am looking at for the amount of work i do.