Hi Chaps , as some of you will know I have had a problem with an unreliable Fuel Gauge, so I very recently purchased a generic replacement from eBay.
Now I know that my “Reserve” Tap supplies Two gallons , so my question is, does the Two gallon reserve start at the Empty line, of after ? ?

Cheers Al

The fuel guage measures the whole quantity of fuel in the tank which therefore includes reserve - which is simply a second feed pipe the inlet of which is a bit lower than the normal "non-reserve" feed pipe.

Hi Stan, then in theory, when my gauge reads 2 galls, or slightly below, then that should be the time when the” Reserve Knob” should be activated?
In truth, my Gauge has never be accurate since I put my car back on the road in 1991 ! ! Now I’ve got the new sender, I shall install it and see if I am able to get it somewhere near accurate !

Cheers Al

Well. .............................. No!

You see the sender unit in the tank is merely a variable resitance, and the fuel guage a voltmeter with different markings - so as the fuel level drops the resitance gets more and the (voltmeter) fuel guage registers a lower (voltage) value.

As the fall of the sender unit float is near linear, however, unless you have a fuel tank with a uniform cross-section, the guage will not be that accurate - notwithstanding the fuel slopping about as it gets low.

Imagine a circular tank end-on where the cross-sectional measurement varies with the vertical distance and you'll see what I mean.

Best thing is wait until you run out of fuel and note the fuel guage reading as you switch to reserve, as this will give you the best indication for future reference - remembering that guages are not really that accurate!