Oddly enough, this came up when I was having Frank Condelli service our '91 last month, and he mentioned that that the 'saddle' or cavity was not only needed for the heating ducts for the air cooled engines, but also for the gasoline or diesel powered auxiliary heaters that were often fitted to the Wasserboxer T3s in Europe.  Since VW was trying to control costs, they wouldn't have wanted to have two different fuel tanks for the Wasserboxer - and I suppose the aftermarket suppliers would do the same (plus the NHTSA testing and liability issues mentioned by others).

James
'91 Westy Weekender
Ottawa, ON

> Date: Sun, 20 Jul 2014 21:19:33 -0300
> From: RNicholl@NBNET.NB.CA
> Subject: Re: Replacement fuel tank question
> To: vanagon@GERRY.VANAGON.COM
> 
> I find it strange that the aftermarket providers who continue to manufacture fuel tanks for these vehicles continued to keep the "saddle" in their construction.   A few quick measurements of the tank dropped from the '88 indicates one could expect 14-18 additional litres of fuel if they were not there and the tank would be simpler to manufacture.
> 
> 
> On 20-Jul-2014, at 20:50, Stuart MacMillan wrote:
> 
> > No, and blame Volkswagen for introducing the vanagon with the obsolete air
> > cooled engine.  Was not worth it for them to re-tool for a couple more
> > gallons of gas.
> > 
> > Stuart
> > 
> > -----Original Message-----
> > From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> > Roy Nicholl
> > Sent: Sunday, July 20, 2014 12:28 PM
> > To: vanagon@GERRY.VANAGON.COM
> > Subject: Replacement fuel tank question
> > 
> > All,
> > 
> > Does anyone make a replacement fuel tank for the water-cooled Vanagon w/o
> > the cavities/moulded passages for the air-cooled heater pipes.  While I
> > appreciate the needs of the air-heads, I would prefer the extra range this
> > capacity could provide if that volume was on the inside of the tank.
> >