You will notice little difference in economy if any at all, unless you go to a real synthetic like Amsoil. Then you might notice a few tenths of a mile increase.
It has everything to do with technical data. How well it will protect your engine, and how long you can run it (the drain interval). Rotella T carries the new CJ-4
API rating which provides more protection. Yet it is the same price as the Delvac you're running now, but it is better oil, and that's based on facts not just my opinion. The new CJ-4 Rotella is superior.
Basically when you go to the store to buy oil, ignore everything written on the bottle except for the letters in the little API circle on the back. Everything else is marketing.
Even if it has other certifications written on the bottle, you go by what is in the circle.
It will say
CJ-4, or CI-4 plus, ect. The oil is certified to meet that spec.
** What you want is CJ-4 **
If you do research you might find one or two negative opinions about CJ-4 oils, mainly because people are ignorant, and they bashed the new rating before the oils were tested. I understand the motive behind that, because the CJ-4 spec does limit the amount of certain additives which are added to oils when they're made, since CJ-4 was designed to meet 2007+ diesel engine specs which run on
ULSD. It is safe to run CJ-4 in older engines, because
it exceeds all previous ratings! Many
oil analysis reports have been done on it and the CJ-4 oil is proving to be great oil.
In simple terms the CJ-4 oil is a semi-synthetic, but with a real cheap price tag.
Now synthetics are a different ball game. It gets way more technical and other things come into play. You have to determine the
base stock the oil starts out with. Rotella 5w40 is a
group III (3) oil, which is just a highly refined (
hydrocracked)
petroleum base oil (comes out of the ground). Amsoil is a
group IV (4) (
100% synthetic PAO, made in a lab) and is WAY, WAY better! The better the base stock (base oil) the more resistant the oil is to break down, the better protection it offers, and the longer you can run it. The viscosity, and additives in the oil however are also very important when it comes to drain interval. The
additives in the oil that allow you to go a while between changes make up what's called the
TBN (or
Total
Base
Number). The total base number is the oils ability to resist alkalinity, or acidic, which softens bearings, causes pitting, ect. The viscosity of the oil is the "thickness" or
pour point at a given temperature. A thick enough
viscosity (but not too thick) will provide a film on the moving parts in the engine. As the miles accumulate the oil gets
sheered down, becoming thinner and thinner. If you start with a 5w40 for instance, it will become too thin much faster than a 15w40 would. This has a lot to do with the fact that a 5w40 is made with a light base oil and it has additives that cause it to thicken after it warms up. To make a make a longer story short those thickeners, called
polymeric thickeners, are only good for so long, and after a while they can no longer thicken to the proper weight. Combine that with normal break down (as the oil "wears out"), your 5w40 that would normally be a 40w when fresh may only become a 20w (half of what it should be) at operating temperature unless it is changed frequently. In the 6.0L for example, this will cause the fuel injectors to not function properly.
So, stick with a
15w40 unless you are in a cold climate, decide what type of you want to run, and make your decision based off that.
If you want to run a cheap oil (by cheap I mean inexpensive) run Rotella T 15w40. I believe it is made up for group II and III's so it's equivalent to a semi-synthetic.
If you want a
REAL synthetic, run
Amsoil AME 15w40
https://www.amsoil.com/storefront/ame.aspx
To get it cheap, sign up as a preferred customer for 10 bucks, and you can get it for dealer price.
Probably more info than you wanted, but you asked for it.
I could explain a lot more and in better detail but don't want to type anymore. I made some key words
BOLD. If you want to learn more about oil type the bold words into a search engine and see what you can find to read.
