Date: Fri, 28 Jun 2002 01:35:46 -0700
Reply-To: Arlen <manx1342@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Arlen <manx1342@EARTHLINK.NET>
Subject: Re: Aux Oil Cooler install...results Aircooled vanagon
Content-Type: text/plain; charset=us-ascii
Well, I find myself compelled to jump in here again, mainly due to the statement "humidity doesn't
matter". In the narrow context that you were talking about (surface contact evaporation) you are
basically correct. But, when it comes to humidity and it's overall effect on cooling, it can matter
a great deal.
Contrary to popular belief, air is less dense as the humidity rises. For proof, just ask any pilot
if they would rather fly on a dry day or a humid day. Take-off rolls are much shorter on a dry day.
Of course, dry and cold is the best.
On to Vanagon content. Most of us are aware of the reason that VW created our beloved (?) liquid
cooled engine. More horsepower! Since liquid is a much better medium for moving heat from one point
to another (hence the water cooled oil cooler), thus more power was coaxed from this (seemingly
ancient*) design. Cooling becomes paramount in direct relation to the amount of work an engine is
required to perform. We all know our Vanagons are heavy and as aerodynamic as a shoe box (gravity
and friction both suck).
I believe this thread started from the addition of an air flow oil cooler on an air cooled engine.
If I were running an air-cooled engine I would do this immediately. One thing to be aware of though
is that it is possible to overcool one's oil, which present other problems. Ideally, the oil cooler
should have a bypass thermostat to maintain a more constant (controlled) temperature. Engines are
designed to be most efficient within a certain temperature range.
Getting back to humidity. If air is used (in any way) as a cooling medium, it should be as
controlled as possible, and the dryer (and colder) the better.
My Vanagon doesn't fly, but I have been working on aircraft for over 25 years. Humidity does
matter!
Arlen
ps: Probably overstating the obvious, again.
*Yes, most non-commercial aircraft still use opposed air cooled engines. Airspeeds are higher,
temperatures are cooler, and air flow through the engine bay is very controlled.
--------------------------------------------------------------------------
Bill N wrote:
> Sounds like the oil cooler is really doing the job. Just a quick note on the physics, though.
> You mention "humid" like it matters. It matters to us because our bodies cool by evaporating
> perspiration, and it doesn't evaporate very well when it is humid. However, the engine isn't
> wet (hopefully) and evaporation plays no part in cooling, so humidity doesn't matter. Since it
> is Friday, I assumed everyone would want to know.
>
> Bill
>
> ----- Original Message -----
> From: "Vanagon man" <vgonman@MSN.COM>
>
> here are the stats. Before the cooler, if i went 70-75 mph in my part of the country (humid,
> and 90+ degrees out side) for any length of time, my oil would hit 110C and probably hit
> 115C.so I had to go more like 60mph. My oil pressure would be more or less equal to my
> rpms(3800 rpm...38psi) and my heads would run between 300-350f.
