Gas Gauge Question

[E. Roy Wendell IV]

On Jan 10, 2007, at 9:55 AM, Mitchell Segal wrote:

> I've noticed something a little funny with my gas gauge lately, and  
> I thought I would ask the group for any thoughts or BTDT on the topic.
>
> My particular issue is, the reading on the gauge seems to move UP a  
> bit once the car is warmed up. For instance, this morning when I  
> first started the car and left the house, the gauge read a little  
> more than 3/8th full.  But when I checked again about 5-10 min  
> later, it's now solidly at the 1/2 mark, even a little more.
>
> I'm pretty sure this has nothing to do with where I'm parking, the  
> slope of the road and such, because I've noticed it for a while  
> now, no matter where I park.  It almost seems to me like either the  
> gauge or the sender in the tank gradually goes up a little bit, as  
> the units warm up.  I might say that this is happening more in  
> colder weather than warmer, but I can't be sure, I don't recall how  
> long it's been like this.
>
> Does this make any sense to anyone?  Does say the sender unit in  
> the tank change readings after it's been "on" for a while, thus  
> heating up what ever electronics are in there, and changing the  
> reading?  Would the gauge change readings depending on it's temp?
>
> In the chance that I'm not imagining things, and it's not do simply  
> to the angle of the car on the various roads (I do know that when  
> the car is tilted up/down/left/right, it can change the readings),  
> is there anything you can suggest I check first, to see if it's a  
> mechanical problem?
>
> I will pay more attention to making sure I park on a level surface  
> for the next little while, as I know that can affect the level  
> reading at rest, and the gauge has a delay built in to it, so that  
> sloshing doesn't affect the readings.
>
> Thanks for any thoughts on the subject.
>
> Mitchell Segal
> 2001 A4 1.8Q
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Had you owned an older car this would be an easy answer. They use a  
heated bimetallic strip to move the needle and are thus sensitive to  
the interior temperature of the car to some extent. The variable  
resistance of the sender changes the current through the heating coil  
wrapped around the bimetallic strip which then changes in temperature  
and therefore position. My understanding is that all the newer cars  
used much more sophisticated gauge movements along the line of  
computer controlled stepper motors and the like although that may  
only be for the speedometer and tach.

Roy Wendell
erwendell at mac.com
Too many type 44 tq
A pair of MR2s