[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: Bob's Synthetics Post
>Ovbiously, Bob Cohen was MEANT to be part of this group - after all,
>he's a "Bob"!! (Bob, if you don't get this - it's a tradition on
>this list...welcome.)
Thanks, I've been popping up for a couple months, now. Since I bought my 91
CoupeQ. It's nice to have a support group.
>Relative to your post, would you share with us your opinion on the
>following subjects:
My opinion isn't really worth much here, but I can try to pass along some
general empirical information if I can find it, and have the time to type
it in along with some background information needed to properly interperet
it.
>1) Ability of the four classes of synthetic base stocks to reduce
>volatilization under the heat and stress of engine use - COMPARED to
>whatever "typical" petroleum oil you care to cite?
In _general_, synthetics are less volatile. I have some _rough_ numbers
here, and they are-
ASTM distillation @ 1mm Hg
Volume Vapor Temperature C Vapor Temperature C
% Distilled 200 N Mineral Oil 150 N Polyolefin
0 194 204
5 205 217
10 210 221
15 212 226
20 214 229
25 215 230
30 216 235
35 218 237
40 219 240
45 220 252
50 223 260
>2) Ability of the synthetic base stocks to maintain engineered
>characteristics of flow and lubrication under extended (10K+)
>service?
Synthetics _generally_ have a higher viscosity index (ex. 130 or so for
PAOs) compared to around 100 for petroleum bases stocks. VI measures
viscosity variabilty with heat. Higher VI = more constant viscosity from
low to high temp. This means fewer viscosity modifiers (generally long
chain polymers) are needed to achieve proper VI in the final blend, when
you start with synthetic base. Vis modifiers are used up (broken) with use.
So, I think it would be safe to say that _viscosity_ might be more
consistant with a synthetic base oil vs a petroleum base through an
_extended_ drain interval. It would not neccessarily be true, though, that
viscosity would be more consistant with synthetic if the recommended drain
interval was observed. Also, the _lubrication_ properties of the respective
oils is beyond my ability to answer at this time, and could turn into a
very complicated response. There are alot of variables (additives,
useage/duty, how do you measure, etc) that have bearing 8-) here.
>3) Ability of synthetic base stocks to resist breakdown under
>unusual heat, such as an overheated engine, as COMPARED to petroleum
>oils?
>
****Unsupported opinion alert*****
Synthetics (I think) are more resistant to coking in the passages than
petroleum base stocks. I don't have any evidence of this, that I know of.
This is purely hear-say as it comes from me. When I ran a turbo car, I used
synthetic. I don't at this time.
******
Generally speaking, carefully formulated additive packages do their jobs
pretty well, so the oil you put in your car works well whether its a
petroleum based oil, or synthetic. It would be a ***grave*** mistake to
overgeneralize from the characteristics of the base stocks to the
charcteristics of the blended oil.
It is vital,though, that drain intervals be monitored closely. For most
people, it's probably more important to change oil regularly, than to
switch to synthetic. Stable viscosity is only _part_ of what makes a good
oil. More on this later.
Regards,
Rob
Disclaimer- I do not speak for Lubrizol.
_____________________________________________________________________________
Robert S. Cohen
NewMedia Inc., 503 E 200th Street, Cleveland OH 44119-1545
voice 216.481.7900 fax 216.481.1570
The Lubrizol Corp., 29400 Lakeland Blvd MS 228, Wickliffe OH 44092
voice 216.943.1200 x 2012 fax 216.943.7215
Email: rsco@lubrizol.com rsc2@po.cwru.edu cohen@nmedia.com
____________________________________________________________________________