Forum registration by new users: Guests should use the Register button top right but if you have difficulty Email mail @ chalkevalley.info (delete spaces).
If you would like to join the DLOC, please visit the Club's website https://www.dloc.org.uk/
Please don't post someone's email address. Some people don't want to risk it being harvested by spambots and GDPR regulations discourage it.
Always look at "ACTIVE TOPICS" which gives all posts in date & time order if you can't find a post or "Your Posts", as topics are sometimes moved.
Reg. nrs. Please add reg. nr. when posting a photo or anything about a car as this will help searches. Don't add punctuation next to nr. as this negates search.

Fuel Gauge Conundrum

Technical issues not related to a DLOC car marque, eg tyres, ethanol, other car makes, etc. and legal, political and insurance
Post Reply
JT7196
Posts: 1054
Joined: Sat Feb 13, 2016 7:22 am

Fuel Gauge Conundrum

Post by JT7196 » Fri Jun 14, 2019 10:36 pm

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 😊😊😊

Stan Thomas
Posts: 534
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Fuel Gauge Conundrum

Post by Stan Thomas » Sat Jun 15, 2019 6:25 am

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.

JT7196
Posts: 1054
Joined: Sat Feb 13, 2016 7:22 am

Re: Fuel Gauge Conundrum

Post by JT7196 » Sat Jun 15, 2019 9:55 am

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 😊

Stan Thomas
Posts: 534
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Fuel Gauge Conundrum

Post by Stan Thomas » Sun Jun 16, 2019 12:25 pm

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!

Post Reply