generic A4 questions

[Huw Powell]

> Most of the below may be true, but are not the germain points.
> 
> 1.) oil may be under pressure, but may not flow freely into the smallest 
> of bearing openings.

Hence the point about 5w (or 0w).  It is at least made to flow 
"reasonably well" at low temps.  Of course, part of the reason for the 
pressure is... higher viscosity when cold.

> 2.) More importantly, at low temperatures, if gaps already exist in a 
> film of oil, its a weak spot and the partial film may tear under 
> pressure (shear)
> 
> 3.) Most importantly, and rarely understood, and clearly stated in my 
> original, by the way, the parts dont fit until warm.  Bearing 
> tolerances; piston/ring/cylinder tolerances and every other tolerance is 
> OFF.  In general they are TOO BIG. Think about this.  I dont have time 
> to do a physics course in an email

And we don't need the condescension, either.  Combine 2 & 3 and the 
problem is not as bad - slightly larger spaces where oil has to flow 
make it easier for it to get there.  Also, these tolerance issues have 
been getting better every year.  My '57 Trojan needs 30 weight to make 
"any" noticable oil pressure (on an Audi gauge...).  Modern cars are so 
tight they can run 0w20 oil for efficiency.  Also, some, at least, if 
not almost all, of these tolerances can be designed to expand "together."

I remember that I think even Audi said not to push the old 2.1 too hard 
when cold because the cylinders actually start out oval, and you'd get 
increased wear leading to increased oil consumption.  Those engines are 
now over 20 years out of date, though.

But - I am also not, as I said, running a turbo engine while doing this, 
and I also think that of the two waiting times (start, stop), cooling 
off is far more important to that hot little turbo after you arrive, 
since that's when coking occurs.

> To huh's point, I would guess, but cannot prove, that even after 2 min 
> things are far better off.

However long it is, it's sometimes almost a red line drag race 
"immediately" after starting.  But if I had a turbo engine, I'd probably 
be able to be courteous to those behind me without using "full pedal." 
All I gots is 130 hp give-or-take in an old 90Q.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/