This is a discussion on Oil weights and cam wear within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Interesting read by Drivbiwire...yes it's a TDI forum...
Interesting discussion there. A couple points:
The discussion focused on whether a 30w or 40w oil is better for long-term cam wear, and the evidence provided was a series of admitedly spectacular photos. Yet this is still a (relatively) macroscopic analysis. Why not use molecular data since it's available and more precise? EDIT: I see the point about a ferrography test needed, but that's IMO reasonable and if everyone there agrees to a standard method to judge stuff, they could figure it out quickly and arrive at an oil that works for most people I guess. EDIT2: Given what was stated -- that particles larger than 4 um cannot be IDed through conventional oil analysis, light microscopy could be used. Sample the oil, mix, throw under a scope, count particles per 100 um square etc.
Nobody seems to consider that the Mobil 5W-40, used over a decent mileage interval, will *not* be a 5W-40 for very long! If you look at the data I posted last week, in my EJ205 motor and in my hands, the 5W-40 at 5,800 miles was (guess what?) a 5W-30. Let's assume the 5W-30 oil is responsible for more wear. Is this because it in turn shears to a 20W, or is it because of some other reason? Will a sheared-down formerly 40w oil that's now a 30w also generate the same wear if left in the motor? Will a sheard down formerly 30W circulate better and generate less wear as a 20W? Both? Neither?
See what I'm trying to say?
If there are a dozen members in that group actually interested in this stuff, maybe they might want to run 1,000 miles on an oil to be tested as a flush period, then change oil using the agreed upon type/grade, and run 7,500 miles on it. They could then send out samples to two or three different labs (or even a single trusted lab if they've agreed to one) and see what's up.
If it were me, I'd stick with a VW505.xx approved oil at 5W-40, but that's just because I'm quite conservative.
Last edited by SD_GR; 08-26-2004 at 02:12 PM.
And a question:
Wouldn't particles over 4 um, that are essentially visible particles under light microscopy, show up as insolubles in conventional analysis results? Much larger than that and the filter would catch them I know.
Yes they would show up much like finding undesolved sugar crystals in sugar water that was saturated....just on a much smaller scale. The oil will always be sheared to a lower weight, but I figure the engineers took that into account when recommending 30W when all thats needed to properly protect the engine is 20W
*GET YOUR CLUBWRX KEYRING*
That makes sense. So the VW group could get an idea of what's going on by combining all those methods. Interesting.
Different oils behave differently, and although one might see shearing down initially, these guys (and I) am prone to not waste good oil, so they may run as long an interval as permissible by their warranty. I do know that some oils (M1 0W-40, for example, and I also think 10W-30) initially shear down but then, as the interval goes on, thicken back up (!) so at least theoretically it's possible to have at least 3 grades of oil within the same drain interval...
Other brands don't exhibit this behaviour, and tend to stay in grade (Amsoil from what I hear). It's unclear to me what's better and why though.
Yeah, I did have the impression that they all drop weight with time and as for increasing back up, did you ever think that the particulates that build up in the oil may be the cause?
It would make sense that as all those insolubles build up nearing 5000 miles would produce a sludging effect at a microscopic scale and on the macro scale makes the oil increase in W.
*GET YOUR CLUBWRX KEYRING*
I thought it might be something to do with temperature and oxidation along with additive depletion over many use cycles etc., I hadn't considered that.
While I do not disagree that oil weights would general lessen between the time they are poured, and a few hundred or even a throusand miles between maintenence, then the question becomes, is this not expected and normal. Some individuals run widely differnt oil weights on this board. Who is to say if you are buying a recommened 5-30 that in fact the oil becoming say 5-20 is not normal and acceptable.
Oil thickening due to particulate matter is not a concern in gasoline engines. Diesels...yes.Originally Posted by BrandonWRX
Oil does break down due to shear, but additives are added to prevent it.
What really causes the oil to drop in "weight" is due to gasoline dilution commonly associated with frequent stop and go driving, which is normal