mono-grade oil requirement DD two stroke diesels?
mono-grade oil requirement DD two stroke diesels?
(OP)
I'm trying to find out the root reason why Detroit Diesel two stroke engines require, to this day, mono-grade engine oil, normally straight 40 weight. Empirical evidience, supported by recommendations from DD, is that the engines last longer between rebuilds using straight weight oil in normal service. I just don't understand why. what is there about a two stroke application that would make a multi-grade oil, of completely modern and high quality manufacture, less protective in this application?
The "common knowledge" answer seems to be that multi-grades revert to their cold viscosity under the pressure of two stroke compression cycles, that the hydrodynamic layer of oil in the bearings can't recover between power strokes, or that the long-chain molecules used in viscosity modifiers shear and break down. I just have a hard time lend credence to how a two stroke diesel, with 18:1 compression, running at 2100 rpm is that different from some other high duty engine requirement.
Any ideas?
Thanks for looking, Brian
The "common knowledge" answer seems to be that multi-grades revert to their cold viscosity under the pressure of two stroke compression cycles, that the hydrodynamic layer of oil in the bearings can't recover between power strokes, or that the long-chain molecules used in viscosity modifiers shear and break down. I just have a hard time lend credence to how a two stroke diesel, with 18:1 compression, running at 2100 rpm is that different from some other high duty engine requirement.
Any ideas?
Thanks for looking, Brian





RE: mono-grade oil requirement DD two stroke diesels?
RE: mono-grade oil requirement DD two stroke diesels?
I did a lot of research and I don't exactly remember what the actual reason was, but the final analysis was that mono grade was the only way to go.
As a personality, I am one that doesn't take no as an answer very well, and I finally threw in the towel on this one.
I remember one website called "bobistheoilguy" dot com or something like that and there was a Shell site or a site by a Shell technologist, and it was dealt with in both places but alas, mono-grade was the only way to go.
Wish I could offer you some encouragement but I can't. Sorry.
rmw
RE: mono-grade oil requirement DD two stroke diesels?
RE: mono-grade oil requirement DD two stroke diesels?
Brian
RE: mono-grade oil requirement DD two stroke diesels?
For VI improvers, generally both types of shear stability are related to cost. There are a host of performance & cost levels available today, meaning that a performance-suitable VI improver could probably be incorporated at some additional cost. Alternatively, multi-vis oils may be prepared without polymeric VI-improvers by utilizing high VI base oils. If you Google 15W-40 with 6V92TA or MIL-PRF-2104G you will find some multi-vis products claiming to meet both 2-and 4-stroke requirements.
RE: mono-grade oil requirement DD two stroke diesels?
I better stop there.
RE: mono-grade oil requirement DD two stroke diesels?
I'm not an expert on this subject, but I have conversed with those who are. One that comes to mind readily is a John Martin. He lives in Phoenix and still (I think) consults. John is an MIT grad that worked years for EMD and then worked the DARPA funded program at Garrett (Honeywell) in Phoenix to build and test a very high performance two stroke diesel. If you can find him, I think he will have an answer.
My limited understanding is that the boundary lubrication issues at the piston pin slipper bearing demand different lube characteristics than typical hydrodynamic lubes, but mine is only a cursory understanding.
Dick