Date: Fri, 14 Jul 2000 14:42:19 EDT
Reply-To: FrankGRUN@aol.com
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@aol.com>
Subject: Bus Depot Fuel Tanks/Baffles and Flow
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Been following this fuel tank discussion and thought I would add some random
observations.
About 6 months ago I decided to renew the seals on the main tank and
particularly the hoses connecting my auxiliary tank to the main tank. As
background, My Westfalia started life as a '82 Diesel delivered in Germany.
In '83 I added a saddle tank reserve (remember the gas crisis?) which is
mounted between the frame and the body edge on the sliding door side of the
vehicle. I converted to a Digifant 1.8 L 8 V engine several years ago. The
total capacity is 26.4 gallons. The saddle tank is not baffled, has a 37.5 mm
diameter connection to the bottom passenger side of the main tank and one 3/8
inch vent line plumbed into the filler pipe vent. The tank has always been a
slow filler and as part of this particular project, I intended to add
additional vents. (Severe masochistic tendencies surface every so often
driving me to attempt improvements ... )
BTW, the non-baffled nature of the saddle tank is a major advantage ... When
stuck in sand or snow, a half full saddle tank (corresponds to about 1/4 full
main tank) really helps push the vanagon free. Little rapid forward then
reverse power sets up, an impressive wave, kinetic energy, out we go. (Sorry,
pitiful attempt at sick humor).
Anyway, as part of this operation I replaced grommets and all rubber,
converted the filler pipe to post '85 standard, and swapped out the diesel
fuel sender with a post '85 gas sender. Somewhere in my noted, I have the
detailed resistive plots for the two senders. The full and empty points are
different and I wanted to exactly match the instrument cluster meter (I use a
post '85 tach unit).
In the course of this exercise, I found that there are three different filler
pipe grommet seals: 1. Large hole, large pipe, 2. large hole, small pipe, 3.
small hole, small pipe. The original diesel tank has a large filler pipe hole
and a large filler pipe. (when I first converted to gasoline, I only replaced
the fuel cap nozzle components (body side of the filler pipe) to provide for
unleaded fillups. The post '85 filler pipe I installed during this operation
required a large hole, small pipe grommet.
I must also say that reconnecting the vent tubes to the top of the tank was
the most miserable job I have yet done on this beast (includes the engine
conversion)!
With the tank down, I cleaned it and inspected the interior with a boroscope
(fiber-optic microscope and camera) There are plenty of baffles particularly
around the sender unit. All of the baffles are spot welded and you can see
the welding pips on the top and bottom surface if you look closely. The gas
sender locked down nicely with the O-ring, but at a different position
(angle) from the diesel. The float swing is different but the baffling
accommodates either.
When reassembled the gauge still shows fuel level changes in going around
corners. The magnitude of the change is largely related to the velocity! If
you are Caspar Milquetoast driving a Waterboxer, carefully watching the
temperature gauge for signs of imminent head destruction thereby cornering at
0.2 G's, there will be a nearly infinitesimal change in fuel level indicated.
If you have installed a 1.8 L 20 V Turbo and are approaching the adhesion
limit of the radials, cornering at 0.86 G's, the fuel level may change by 0.5
tank units. After the adhesion limit, your observations may be faulty.
The point is that the fuel is a very low viscosity liquid and the baffles
only offer a n impedance or resistance to flow. The baffle structure has
significant open areas (not small diameter flow restrictors) between
chambers, so the baffles dampen the slosh - don't prevent it.
BTW several baffles went floor to ceiling so they might best be described as
stiffeners for the tank.
Of course, this has nothing to do with Ron's tank as I have never seen one.
Nonetheless, If needed I'd purchase one of these in a minute as compared to
the factory unit. After all, the essence of the tank is containment, and both
the fuel gauge and the sender will function better if continually moving!
Mechanical dead spots on resistive element ...
Sorry, couldn't help myself.
Frank Grunthaner