oil analysis - 6k OCI on Delvac 1 in a 617 turbo - Page 3 - PeachParts Mercedes-Benz Forum

JHZR2 · #31 05-30-2004, 08:17 AM

Well, here is the thing... Rotella T synthetic and Chevron supreme synthetic are both Group III base oils. This means that they are more or less 'fake' synthetics, as their precursors are the byproducts of the crude refining. Gropu IV oils like mobil, for example, start with an ethylene gas to synthesize their oil.

Thats why group IV (PAO) and V (ester) oils are so $$$. And therein lies the problem. WHile mobil, amsoil, redline, etc were selling oils that had a truely synthesized basestock that probably costs $3 wholesale, castrol many years ago began selling a group III 'synthetic' oil that they could sell at $3/qt at the point of sale and still make a profit. Mobil sued castrol, castrol won, and so group III oils can be called synthetic, and sold right along side of the real ones. And castrol sells them at the same price.

Now what does this have to do with anything? well, rotella synth and chevron synth are both group III. Fortunately, these companies dont try to rip off the consumer as castrol does, and they sell their oils for ~13/gal. thats pretty fair.

However, group III synthetics can not match up to IV or especially V lubes in cold flow performance. Pour point is only a verylow level analysis of low temperature performance. This is because, at the pour point, the oil WILL be thicker than molasses. It will be just shy of being a solid. Do you want that in your engine?

Dont let viscosity index be a sole determination of a good oil. Often it can hint at the fact that a lot of viscosity index improver has been used, and regardless of how shear stablie it is, in applications such as turbo diesels, Id rather have a more shear stable oil. In an OTR truck its actually easier on the oil than our cars. An OTC truck will spin at 1500 rpm or something like that when cruising at 65. Where are we? 3000 rpm or so?

More important, and corresponding to how the design specs in engines are created with respect to lubrication, is the viscosity at various temperatures, and that reported in the 'ccs' (cold cranking simulator) an MRV (mini rotational viscometer), and in those tests, you can be sure that the true synthetic will show itself. LAst I remember, delvac bested chevron 'synthetic' by about 4000 cP on the test, at -25C.

But oil chemistry is an ever-improving field, and it definitely is possible to make a dino oil which has most properties as good as an actual synthetic. MAybe its even better to have a synthetic with a little bit poorer cold flow properties (i.e. the chevron or rotella), as these engines are designed with certain oil properties in mind.

All in all, the best thing that I could ever say is that there is no right answer. I feel more comfortable using a synthetic in the 617 and drawing out the change interval, than if I did the same with a conventional. I also feel more secure using one oil year round, that I know can work well in the winter, and have the necessary robustness and shear stability to deal with summer heat, protect in the case of an overheat, etc, etc. Although I cant say the same for light duty gas engine oils, where there is a LOT of variability in quality and performance, in the HDEO area there is no bad choice. All of the main oils are really good and will provide excellent results. The choice needs to be based upon success as per oil analysis, fuel economy, drain interval (shouldnt exceed 2% soot regardless, based upon MB specs), cold flow youll encounter, etc. And then you just need to figure out what you want? An oil you know will stand up to being overheated and overused? An oil that will carry 4% soot loading, as opposed to 2%, leaving you a nice dispersant reserve, etc. and it is entirely customizable.

Id definitely have to say that the group III synthetics are appealing, especially considering the price. You get a robust HDEO, with cold flow properties more suitable to winters around here than using a 15w- oil year round, and thatll do well. I have been considering testing rotella synthetic for a number of 3-5000 mile intervals for economy, wear, etc., but have been so happy with delvac, that Im not so sure Ill do that. we shall see.

JMH

Gurkha · #32 05-30-2004, 10:16 AM

JHZR2,

One last question if I may, given the choice between two conventional oil like Delo 400 Isosynth or Delvac Super, which would be your first choice and why and which of these two oils would make you feel comfortable in an extended drain situation of say six months/6500 miles.

JHZR2 · #33 05-30-2004, 10:39 PM

thats a tough one. Io think the two oils are too close to call. Chevron has an excellent basestock, but delvac has moly in it. Ive had better mpg results with delvac than delo. However, Ive always seen excellent wear rates with delo (not sure how they compare to delvac 1300 super though)

Id say go with whichever youve been using for the last number of changes. less chance of additive clash that way. Back up your choice with oil analysis. If you dont like the results of one, do a short interval and then analyze the results of the other oil after 6k or so.

JMH

Gurkha · #34 05-30-2004, 10:46 PM

http://kozmik.guelph.on.ca/gtdproject/fluids/le.htm

Check this link out, an eye opener on the wear rates of Delvac Super and Delo 400.

JHZR2 · #35 08-10-2011, 03:03 PM

Keep in mind that 2004 oil formulations can be substantially different than 2011.

sjh · #36 08-10-2011, 04:56 PM

Quote:

Originally Posted by JHZR2

Keep in mind that 2004 oil formulations can be substantially different than 2011.

Since it is 2011 which oil are you currently using in your MB diesel and how often do you change?