Go Back   The Ford Barn > General Discussion > Early V8 (1932-53)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 10-01-2020, 04:39 PM   #1
19Fordy
Senior Member
 
19Fordy's Avatar
 
Join Date: May 2010
Location: Coral Springs FL
Posts: 10,879
Default Gas Tank Fuel Gauge reading question

If you drain your gas tank on a car like a 40-48 Ford and fill it with water, will the fuel gauge give the same readings as when tank was filled with gas.

I ask this question because I am wondering if the difference in the density of gasolene and water will effect the float level and hence, the fuel gauge reading.

I would like to do this to check the accuracy of my fuel gauge and calibrate my gas tank sending unit.
Density of water is 1. Density of gasolene is .71 to .77 according to Google

Thanks.
19Fordy is offline   Reply With Quote
Old 10-01-2020, 06:57 PM   #2
terry
Senior Member
 
Join Date: May 2010
Posts: 260
Default Re: Gas Tank Fuel Gauge reading question

Given the density figures you gave, I'm thinking your gauge would read a little low. The oil that gas comes from floats on top of water. Just guessing. Terry
terry is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 10-01-2020, 09:12 PM   #3
Zeke3
Senior Member
 
Zeke3's Avatar
 
Join Date: Dec 2014
Location: Columbus, IN
Posts: 1,401
Default Re: Gas Tank Fuel Gauge reading question

I think the float will sit a little bit higher in water than in gasoline because it will not have to displace as much water to reach the point of equilibrium, so your gauge readings would be slightly higher with using water. I am guessing that the difference in the float depth is probably pretty small compared to the overall range of the float travel of the sending unit from full to empty.

Michael Driskell posted his gauge calibration process for a resistance stlye sending unit in the recent discussion about replacing the fuel tank on a 1947 car, post #14 in the attached link.

https://www.fordbarn.com/forum/showthread.php?t=287943

Last edited by Zeke3; 10-03-2020 at 09:34 AM. Reason: Added link.
Zeke3 is offline   Reply With Quote
Old 10-01-2020, 09:18 PM   #4
JSeery
Member Emeritus
 
JSeery's Avatar
 
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
Default Re: Gas Tank Fuel Gauge reading question

Well, it is going to be different, but the question is, is it different enough to worry about? Not sure of the answer, but thinking about it I would think the float height is only going to change a % of it's diameter. Might run an experiment with the float in a small container of fuel and then water and see if the difference is apparent and measurable.
JSeery is offline   Reply With Quote
Old 10-01-2020, 10:33 PM   #5
Phil Gillespie
Senior Member
 
Phil Gillespie's Avatar
 
Join Date: Sep 2011
Location: Christchurch New Zealand
Posts: 1,603
Default Re: Gas Tank Fuel Gauge reading question

What will affect the postion of the float in the liquid it sits in is the liquids Specific Gravity.
This also changes with temperature.
But in this case maybe using 25 degrees celcius
SG of fuel is .713. as opposed to water at .997.
Float will sit higher slightly in the liquid qith the higher SG.
In this case will not make a lot of difference as will be constant for liquid being used.
ny thughts.
Phil NZ
Phil Gillespie is offline   Reply With Quote
Old 10-02-2020, 08:13 AM   #6
glennpm
Senior Member
 
glennpm's Avatar
 
Join Date: Sep 2014
Location: Wiscasset, Maine
Posts: 1,965
Default Re: Gas Tank Fuel Gauge reading question

Sponsored Links (Register now to hide all advertisements)
Hi Jim,


It will make a minuscule difference. The main height in whatever fluid will be the same. The only difference will be the float itself and how much it will displace the fluid. Water has higher density than gasoline so the float weight won't displace as much water as it does for gasoline.


Glenn
glennpm is offline   Reply With Quote
Old 10-02-2020, 12:15 PM   #7
19Fordy
Senior Member
 
19Fordy's Avatar
 
Join Date: May 2010
Location: Coral Springs FL
Posts: 10,879
Default Re: Gas Tank Fuel Gauge reading question

Thank you all for taking the time to answer my question. I never got good grades in physics so your info. was very helpful. Nice and simple.
Jim
19Fordy is offline   Reply With Quote
Old 10-02-2020, 12:40 PM   #8
Lawson Cox
Senior Member
 
Lawson Cox's Avatar
 
Join Date: May 2010
Location: Above the gnat line in Georgia
Posts: 7,009
Default Re: Gas Tank Fuel Gauge reading question

What a useless discussion. What difference does it make? The car ain't going nowhere on water, regardless of what the gauge reads. ROFLMAO
__________________
Life is like a roll of toilet paper. The closer to the end, the faster it goes.

It is better to be seen, than viewed.

"We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm".
Lawson Cox is offline   Reply With Quote
Old 10-02-2020, 12:49 PM   #9
19Fordy
Senior Member
 
19Fordy's Avatar
 
Join Date: May 2010
Location: Coral Springs FL
Posts: 10,879
Default Re: Gas Tank Fuel Gauge reading question

Lawson, Not useless to me. I wanted to use water because it would be a lot easier to fill and drain the tank in the process of recalibrating my fuel tank sending unit by turning "ON" the ignition switch, not driving the car. I just wanted to know if there would be a big difference in readings obtained using water.
19Fordy is offline   Reply With Quote
Old 10-02-2020, 02:26 PM   #10
hotrodart
Senior Member
 
hotrodart's Avatar
 
Join Date: May 2010
Location: Shenandoah Valley Virginia
Posts: 220
Default Re: Gas Tank Fuel Gauge reading question

The accuracy of the 80 year old technology in that gauge is significantly less than the measurable difference in the float levels with those specific liquids.
hotrodart is offline   Reply With Quote
Old 10-02-2020, 04:16 PM   #11
19Fordy
Senior Member
 
19Fordy's Avatar
 
Join Date: May 2010
Location: Coral Springs FL
Posts: 10,879
Default Re: Gas Tank Fuel Gauge reading question

I now agree. I ended up draining the tank and then refilling it 1 gallon at a time checking the gas gauge reading after each gallon of gas was added. Thanks again to all who responded.
19Fordy is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 12:34 AM.