Date: Thu, 13 Sep 2007 11:50:49 -0700
Reply-To: David Kao <dtkao0205@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Kao <dtkao0205@YAHOO.COM>
Subject: Re: DOn't use SM rated oils Re: Flickering Oil Light 84 auto
In-Reply-To: <20070913181134.599F81165C3@hamburg.alientech.net>
Content-Type: text/plain; charset=iso-8859-1
--- Mike S <mikes@flatsurface.com> wrote:
> At 01:32 PM 9/13/2007, David Kao wrote...
> >I have long suspected why the Vanagon community strongly recommend
> >20w-50 oil and everybody buys that. I do not intend to start a war
> >on oil weight discussion. But 20W-50 dino oil means 20 weight oil
> >in winter (50 in hot summer).
>
> No, 20W is the viscosity rating at -10C, 50 is the viscosity rating at
> 100C (approximate engine operating temperature).
20W is the base weight of the oil before heating up. Its viscosity is too high
for cold start in cold winter mornings. That's what I have doubt in mind about
20W-50 oil. I think everyone pretty much understand that most of wear of an engine
is in the first 5 miles of driving after a cold start in the morning. That's when
the engine needs to most protection form a proper weight of oil.
> Unless your engine
> doesn't heat up in the winter (i.e. the oil stays _cold_), the
> viscosity at operating temperature doesn't change much by season.
>
> http://www.maintenanceworld.com/Articles/thibault/HowToRead/read_oil_can_tab2.gif
>
> >Yes, heavier weight oil increase oil pressure but if it does not flow
> >fast enough to replenish the oil between metal surfaces high oil
> >pressure
> >itself is useless.
>
> It's not like there's an empty space (vacuum) in the bearings, just
> waiting for oil. Once the oil is pumped up, it's oil displacing oil.
> The reason oil pressure goes up is because it's harder to get the oil
> _out_ from between the bearing surfaces to make room for more.
The pressure in the bearing is extremely high. Oil is easily forced out
fast when the crank is turning. With higher viscosity oil pressure goes
up because it is harder to get into the bearings. Establishing a protective
layer fast in between metal surfaces is the purpose of lubricant. The
layer of oil is constantly depleted by the extreme pressure in the bearings.
You want the oil to be replenished fast. You will want the oil to flow fast.
I doubt that 20w-50 oil serves that purpose well at cold start situation
in winter.
> There
> are two issues with high weight oils: upon startup they don't pump up
> as fast, which is why there is a "20W" spec (so it flows better when
> cold), and they are of course more viscous, which doesn't mean they
> don't protect from wear as well, but that they take more work to move,
> which affects gas mileage. Higher weight protects from wear better, but
> with more friction.
>
If higher weight is always better why not move to 30W-60? Why there are not
30W-60 oil in the market? I don't think higher weight is better. The question
is which weight is best for Vanagon. Most new cars these days recommend 5W-30.
These cars are more powerful and spins at higher RPM. Yet they require lower
weight oil. I doubt Vanagon engines are hotter. The water jacket design should
really keep it cool. Even it is hotter, the 20W part of 20W-50 does not help
the cold start need of the oil. 5W would be much better for cold start.
David
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