Date:         Thu, 19 Aug 2010 14:58:03 -0700
Reply-To:     "Michael A. Radtke" <wa7zpu@CISAZ.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Michael A. Radtke" <wa7zpu@CISAZ.COM>
Subject:      Re: Heat, vapor lock, won't start?
In-Reply-To:  <AANLkTin-b_VgEx5b4J9m1bTYFwsbyj=-cSmK9Lg_28Du@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Thanks for your comments Michael.

Unfortunately it's been too long ago to remember a lot about the event
and I looked for the service record but didn't find anything.  I do
remember that it was 100+ degrees and high altitude, but we have both of
those in AZ as well and I never had a problem.  However, the gasoline
blend might have been the issue since the high temperatures are usual in
AZ but not in ID.

Another post mentioned that the fuel injected system was positive
pressure so vapor lock was unlikely.  In the Vanagon's case, the run
from the tank, through the filter, to the fuel pump, is just the
pressure of gravity.  And, the friction through the fuel filter might
cause negative pressure in the pump.  If the gas boils there, it could
cause the pump to lose its prime and the vapor bubble could block the
fuel from moving through the filter and the suction side fuel line in
much the same way a coffee percolator works.

The usual cause of vapor lock on carbureted cars with an engine mounted
fuel pump is well understood.  But, I recently observed vapor lock on a
gravity fuel system on a 2KW generator.  The unit has a clear fuel line
and clear fuel filter, so I could see what was happening.  If I hadn't
seen it, I wouldn't have believe it possible.  The fuel line drops from
the tank through a filter to a shut off valve mounted below the
carburetor.  From there it continues up to the carburetor which is still
6 inches below the tank.  In hot weather, the gas boils in the fuel
filter and the gas vapor fills the filter and creates vapor bubbles in
the fuel line.  Either the bubble in the filter blocks the flow, or
there are enough bubbles in the downward sloping fuel line to reduce the
pressure in that segment to less than the pressure in the fuel line
segment going back up to the carburetor.  Either way, the engine stops.
  With the gas cap off, a steady stream of bubbles can be observed
coming from the fuel outlet into the tank.

Now I suppose if there were dips in the Vanagon fuel line to the pump,
the dealer could have shortened and straightened it to improve the
situation.  But, I am sure that he said that he drilled something.  I
hope that he didn't just drill a hole straight through the fuel filter.
  That's something that I would have never noticed, and might actually
have fixed the problem.

Mike

-------- Original Message --------
Subject: Re: Heat, vapor lock, won't start?
Date: Thu, 19 Aug 2010 15:39:10 -0500
From: Michael Sullivan <sandwichhead@GMAIL.COM>
Reply-To: Michael Sullivan <sandwichhead@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM

That is the kind of exacting fix we need to hear...regardless of wether you
know the fix they did(but it would be nice if you could check your/dealer
records and confirm ) cuz it sounds like this is either an elevation or
regional fuel issue.  Am I right?.
Michael in San Antonio
91GL Weekender AT 2.1L 'Gringo'