Date:         Mon, 12 Apr 2004 12:17:32 -0400
Reply-To:     Sam Walters <sam.cooks@VERIZON.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Sam Walters <sam.cooks@VERIZON.NET>
Subject:      Re: back heat removal, comparative experiences among my vans
In-Reply-To:  <90.44c4c94c.2dac0589@aol.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Dennis Haynes wrote:

"There is no reason to shunt the heater. Cap off the hoses or
better yet, remove the tees and replace with straight fittings. Shunting
the rear heater will reduce flow to the front heater and yes, it will
also reduce available flow through the radiator."

and Ben T wrote:
"You would be better off closing each end with a cap. Connecting them
the way you have alllows the coolant to bypass the radiator. Water take
the path of least resistance."

Both of you have more experience at this stuff than I do, but I will
offer a somewhat different view.

Basic physics - larger pipes and openings have much less resistance than
smaller ones.

And the much larger pipes and hoses carrying coolant to the radiator
offer significantly less "resistance" than the smaller hoses going to
the front and rear heaters.  While some of the coolant will flow through
the rear heater hoses if they are left in place connected and thus
return to the engine without having been to the radiator, all of it will
not circulate through there and bypass the radiator.  Given the size
differential of the pipes,  most of it will go to the front and the
radiator as that is the path of least resistance.  Coolant will still
flow straight through the T toward the front heater even though some
will make the 90 degree turn into the rear heater loop.

In addition to thinking about it from a physics perspective, I have some
practical experience:

Some PO (2nd back I think) took the rear heater out of my 85 weekender.
The hoses are connected under the rear seat with a short metal bypass
tube.  The van runs very cool and the front heater works fine.  In fact,
it seems to heat up the front as fast as my other vans.  Didn't miss the
rear heater this past winter but had thought I would.

It did get a new radiator and new hoses and pipes when the most recent
PO had a rebuilt engine put in about 20 months ago, so the flow to the
front is better than if it had old original ones.  Let it sit in traffic
a few minutes and the needle moves to mid LED and the radiator fan
begins to cycle on and off in response to the switch that is in the
radiator IIRC.  Coolant temp indicator in the dash relaying signal from
measurement on the engine responds quickly and consistently to this and
even more from beginning to move the van steadily, dropping from mid LED
to half needle width below LED.   So plenty of cooling is being done by
my radiator.

I have sat through several major traffic jams in hot weather with no
indication that the van wasn't moving sufficient coolant to and from the
radiator.  Needle point never has gone past the LED in those
situations.  But it did zoom past there in a few seconds when the fan
belt broke last September, so I know it works as designed.  (Quick off
and to side of road, so no problem from that.)

I am not asserting that this is the best setup.  Removing the T's may be
better to some degree in the long run, but just saying that we should
not overstate the impact of the simple bypass solution given the
differentials in hose sizes, the straight flow to the front heater, and
this data.

Based on my actual experiences and the lack of any observed differences
from my other vans (almost 19 years of daily driving of one or the other
of them), I had not even thought of this as a potential problem for my
van or Kirk's 'Mexico in winter' trip until I saw Dennis Haynes' post
last night and have thus been thinking about how this van cools itself
in comparison to my other two since then.

Open to rethinking this though.  But, if there is any difference, this
van seems to run cooler than the others, but I know the indicators
aren't extremely accurate and it is a new engine with a new radiator and
hoses, etc., so there are lots of variables.

Sam

--
Sam Walters
Baltimore, MD

89 Syncro GL
85 Westy Weekender
84 Vanagon, original owner, soon to be retired, just too many problems

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