[Vwdiesel] Vwdiesel Digest, Vol 42, Issue 27 (fwd)

[Val Christian]

Higher vis oil, combined with leaky rings, can aggrivate carbon
buildup in the ring area.  This have the effect of increasing the
leakage, by making the ring "sticky" in the groove.  A lighter oil
may reduce the effect.  This is counter general wisdom, which has
always been, higher viscosity oils in older engines.

I don't have quantative results on this, although I have heard of the
effect, and observed it in some of my earlier diesel Rabbits.  I used to 
run 20W-50 in all my VW diesels years ago.  If anyone comes across
any peer reviewed papers on this, I'd be interested.

Some reasons for running lighter vis oils include: increased cooling
(particularily in high performance engines), improved fuel economy,
Higher vis oils tend are thicker at high temps, hence a good argument
for a multi-vis oil.  I wouldn't consider IDI engines high performance,
however.  And in winter (0F type temps) there is a BIG difference in
starting with a 10W vs a 20W oil.  In my older IDI cars, when I ran 
20W-50, I would change and run 10W-40 in Jan and Feb.  Changing the 
oil around New Years also helped get soot out, which tends to increase
the effective viscosity of the oil at colder temps.  Fresh oil in the
winter, with an older engine helps.

BTW, I think James meant, " Thicker oil works better in bearings
with GREATER clearance."  

Val

Forwarded message:
> 
> Nope.  oil lubricates the cylinder wall.  The seal is effected by the
> pressure in the cylinder pushing outward on the piston ring. Wear,
> warpage, cracking, scoring all effect sealing, but oil viscosity
> isn't really one of them.  Viscosity is more a bearing issue.
> Thicker oil works better in bearings with less clearance.  Motors
> built with close tolerances work better on thin oil- down to 0-40
> synthetic. Older motors with wear and larger bearing tolerances can
> make better use of higher viscosity oil.  Now that's just a rule of
> thumb, there's other factors too...
> 
> -james
> 
> 
> 
> paul lew wrote:
> > I hope I'm not mixing things up, but I would think a thicker oil
> > would create more of a seal from cylinder to piston ring. but yeah if
> > the fuel is not burning fully or the engine has post nasal injector
> > drip it would seep past the rings into the oil.
> > 
> > Message: 2 Date: Thu, 26 Apr 2007 07:18:06 -0700 (PDT) From: David
> > Cook Subject: Re: [Vwdiesel] Any Oil Analysis for xW-30 in a Rabbit? 
> > To: diesel list Message-ID:
> > <777241.64142.qm at web56501.mail.re3.yahoo.com> Content-Type:
> > text/plain; charset=iso-8859-1
> > 
> > How would the oil viscosity determine whether diesel can get into the
> > oil?
> > 
> > Seems like a one-way street to me and I can't figure out how the oil
> > can determine what actually gets in there, seems like things like the
> > rings are about the only thing that could allow diesel into the oil.
> > 
> > 
> > Whenever I change the oil in dad's TDI, it always smells good to
> > me... A little like a charcoal BBQ, but that isn't quite the right
> > description either.
> > 
> > David
> > 
> > 
> > --- Stephen Kraus wrote:
> > 
> >> Over time, the seals will begin to weep oil and the next time you
> >> change your oil, best smell it. If it smells like diesel, time to
> >> go back to 15w40... If I run anything lower than 15w40 the seals
> >> leak and the oil mixes with the diesel. I notice no change in oil
> >> pressure however. -- Stephen T. Kraus Jr. Home: (423)842-5890 
> >> UB3RATL4Sf00 at gmail.com; 
> >> _______________________________________________ Vwdiesel mailing
> >> list Vwdiesel at vwfans.com 
> >> http://www.audifans.com/mailman/listinfo/vwdiesel
> >> 
> > 
> > 
> > 
> > 
> > --------------------------------- Ahhh...imagining that irresistible
> > "new car" smell? Check outnew cars at Yahoo! Autos. 
> > _______________________________________________ Vwdiesel mailing list
> >  Vwdiesel at vwfans.com 
> > http://www.audifans.com/mailman/listinfo/vwdiesel
> > 
> _______________________________________________
> Vwdiesel mailing list
> Vwdiesel at vwfans.com
> http://www.audifans.com/mailman/listinfo/vwdiesel
>