Date: Wed, 20 Jul 2011 15:38:19 -0700
Reply-To: Jake de Villiers <crescentbeachguitar@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jake de Villiers <crescentbeachguitar@GMAIL.COM>
Subject: Re: Watching Oil Temp (long, as usual)
In-Reply-To: <1311194867.15244.41.camel@TheJackUbuntuNetbook>
Content-Type: text/plain; charset=ISO-8859-1
When I reached out on a 98 degree F. afternoon and shot the black asphalt
roadway with my IR temp gun it read around 140 degrees - if the air going
past your sump is 98 and the roadway is 140, that's still a useful
differential from your 220 degree oil, is it not?
My point about the RPM is that a relaxed climb at 3200 won't be building
heat in the engine like 3800 RPM will - that's all. I found that we could
climb longer and cooler at 25 MPH in second gear in the '84 - it took longer
but the van was much happier.
On Wed, Jul 20, 2011 at 1:47 PM, Rocket J Squirrel <
camping.elliott@gmail.com> wrote:
> Drat. I /knew/ someone would question my off-the-cuff "20mph in 1st gear
> statement."
>
> I just tossed out those numbers to illustrate the fairly slow
> groundspeed I find myself climbing desert grades in. Last summer it was
> baking outside as I worked over several steep grades driving south on
> 395 from Pendleton, Ore., to John Day, Ore. -- towing my little camping
> gear trailer.
>
> I ran the engine around 3800 rpm. I posted about this when I got home,
> hoping to sort out a weird issue where the engine died for a few seconds
> several times up each grade, which was pretty nerve-wracking. The exact
> rpm-to-speed numbers are in those posts. I don't normally track the
> relationship.
>
> 3200 rpm would certainly result in a somewhat cooler engine. But that's
> beside the point of my little "airstream" joke. The pavement, just
> inches below the sump, must have been hot enough to bake a pizza on.
> Doesn't seem to me (though maybe someone has some numbers to show
> otherwise) that at 20mph (or whatever you get at 3800 rpm in first gear
> in an AT Vanagon) as much air is slipping past the sump as one would
> hope for in such a situation.
>
> -- RJS
>
> On Wed, 2011-07-20 at 13:03 -0700, Jake de Villiers wrote:
> > When I stick my hand out the window at 20 mph I certainly feel the air
> > going by...
> >
> > What kind of RPM are you using at that speed Mike? I do long steep
> > bits at about 3200 RPM.
> >
> > On Wed, Jul 20, 2011 at 10:27 AM, Rocket J Squirrel
> > <camping.elliott@gmail.com> wrote:
> > "Airstream," he said.
> >
> > Like crawling up a desert grade in 1st gear (AT) at 20 mph in
> > 100 degree F weather.
> >
> >
> > On Wed, 2011-07-20 at 10:13 -0700, Jake de Villiers wrote:
> > > There's some almost information in your post Mike.
> > >
> > > The oil pump moves the oil at a fixed rate whether cold or
> > > hot. Just like your water pump, it increases the rate with
> > > RPMs.
> > >
> > > The sump, whether your finned aluminium VW one or my black
> > > painted steel Subaru one is hanging down in the airstream
> > > for a reason. The cooling air pulls heat from the metal
> > > surface, allowing the heat from the oil to take its place.
> > >
> > > And yeah, the volume of coolant vs the volume of oil makes
> > > the temp gauge cycles very different from one another.
> > >
> > > Happy motoring!
> > >
> > >
> > >
> > >
> > > On Wed, Jul 20, 2011 at 9:10 AM, Rocket J Squirrel
> > > <camping.elliott@gmail.com> wrote:
> > > On Wed, 2011-07-20 at 08:47 -0500, Dave Mcneely
> > > wrote:
> > >
> > > > Bottom line, I think the oil has a major heat
> > > source, and only if an
> > > > external cooler has been added does it have a
> > > real functional way to
> > > > dissipate heat other than to the coolant through
> > > metals that both
> > > > contact and through such things as the sump. The
> > > sump is like a
> > > > reservoir of liquid, it cools slowly compared to
> > > a radiator. The
> > > > coolant has a large heat sink, and thus has a
> > > temperature gradient.
> > > > That gradient includes the oil.
> > >
> > >
> > > So what we're saying is that the oil is in contact
> > > with some really hot
> > > bits, and because there is high thermal resistance
> > > between the oil and
> > > the coolant, the oil can climb to much higher
> > > temperatures than the
> > > coolant.
> > >
> > > It doesn't help matters that the hot oil drains down
> > > to the sump which
> > > isn't cooled by anything except the hot pavement
> > > under the engine!
> > >
> > > Others have also explained that while the water pump
> > > can move a lot of
> > > coolant up to the heat sink in the front, the little
> > > oil pump just chugs
> > > along pushing the oil more slowly and in lower
> > > volume so that even if
> > > there was an external oil cooler the size of the
> > > radiator, the stuff
> > > ain't moving fast enough or in enough volume to cool
> > > the really hot bits
> > > it's in contact with like the coolant can for the
> > > hot bits it is in
> > > contact with.
> > >
> > > I think I've arrived at point where I have a better
> > > understanding of why
> > > the oil temp gauge shows higher peak temps during
> > > high engine demand
> > > than the coolant gauge shows -- which is the answer
> > > to my original
> > > question! Many thanks to all who have taken the time
> > > to respond to my
> > > inquiry!
> > >
> > > -- RJS
> > >
> > >
> > >
> > > --
> > > Jake
> > >
> > > 1984 Vanagon GL 1.9 WBX - 'The Grey Van'
> > > 1986 Westy Weekender/2.5 SOHC Subie - 'Dixie'
> > >
> > > Crescent Beach, BC
> > >
> > > www.thebassspa.com
> > > www.crescentbeachguitar.com
> > > http://subyjake.googlepages.com/mydixiedarlin%27
> > >
> >
> >
> >
> > --
> > Jake
> >
> > 1984 Vanagon GL 1.9 WBX - 'The Grey Van'
> > 1986 Westy Weekender/2.5 SOHC Subie - 'Dixie'
> >
> > Crescent Beach, BC
> >
> > www.thebassspa.com
> > www.crescentbeachguitar.com
> > http://subyjake.googlepages.com/mydixiedarlin%27
> >
>
>
--
Jake
1984 Vanagon GL 1.9 WBX - 'The Grey Van'
1986 Westy Weekender/2.5 SOHC Subie - 'Dixie'
Crescent Beach, BC
www.thebassspa.com
www.crescentbeachguitar.com
http://subyjake.googlepages.com/mydixiedarlin%27
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