Date:         Sun, 14 Jan 2001 23:48:09 -0500
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Fuel Gauge Problem..
Comments: To: Patrick Harris <thunderbirdelectronics@HOTMAIL.COM>
In-Reply-To:  <F148Z9rWjAKYVpMmOlb00001be7@hotmail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 10:59 PM 1/14/2001, Patrick Harris wrote:
>When it gets around 1/2 to 1/4 tank it reads really irratically.  It'll read
>empty, or accurately, or needle won't even come out... I'm wondering if it's
>the sender, gauge, exciter, or what?  Any suggestions?

It's the sender.  I don't know what the failure mode is on Vanagon ones --
on Toyotas the wiper arm wears through, and I have rebuilt those fairly easily.

The gauge can never give an erratic reading that's specific to a certain
amount of gas, because of how it's built:  It's a bimetallic strip with a
coil of thin resistance wire wound around it.  With a full tank of gas the
sender has a low resistance, which allows enough current to flow through
the gauge to heat the strip significantly  (which bends it) and point the
needle to the top of the gauge.  The end of the bimetal strip probably
moves 3/16 of an inch or less -- it's coupled to the needle very near the
bottom end, so its motion is magnified greatly by the needle.

The sender is just a coil of resistance wire with a wiper attached to a
float, so it gives a variable resistance to ground.  If the wiper wears
then things start getting flaky.

david


David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"