Re: [OM] [OT] 20W oil, was spare wheels, deer and BMWs, etc.

[Brian Swale]

Andrew wrote
 
>%> Sounds unlikely. Tolerances shift with the difference in heat expansion
>%> between unlike materials in the engine - such as rings and cylinder walls.
>%> And older cars such as Merc's which had very fine tolerances didn't
>%> specify sewing machine oil (20W). Fussy people swapped a summer grade
>%> (30-50W) for a thinner winter grade (20-40W) but that probably only made a
>%> difference at start up. Allowing the engine to idle to running temperature
>%> before driving off was said to help and taxis which never cooled down
>%> recorded astonishing mileages between reconditioning - up to three times
>%> the norm. But that meant that you were driving off hard on other
>%> assemblies that were still cold such as gearboxes and diffs! And those
>%> have pretty fine tolerances but we're still running 90W in them are we
>%> not?

Sorry Andrew, but I do disagree with you. Talk to a reputable auto-mechanic.

Examples; I had a 3L V6 motor reconditioned very well for a Transit van I had. 
The 
reconditioner was a perfectionist.

So I thought I should use the relevant new oils as used in modern cars ( 
Talking about 15 
years ago now). Put this new fine oil in, and the motor burned / wasted it like 
it was going out 
of fashion. Horrible.
Cure? Drain off that expensive stuff and put in fresh "normal" oil.

Problem solved.

As I understand it, modern motors are designed to much finer tolerances (and 
almost 
certainly different materials especially for rubbing surfaces such as 
bores/piston rings where 
processes such as nitriding (and more recent ones) are used and probably not 
available to 
the backyard reconditioner) that finer oils are mandatory.

"My" mechanic who trained on Beemers, says that even 20 yo Beemers run a heck 
of a lot 
better on the special oils he gets, and my experience bears this out.

My 2 cents' worth ... :-)

Brian Swale

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