Fuel sender/gauge testing...

[rebby]

I ran a bunch of tests on the fuel sender and gauge setup today and thought that I'd share my results with the board.

First, I tested a new 3/8 sender from Kramer Auto in a new tank from Van's Auto (basic $120 tank). I tested this by leveling my fuel tank on my living room floor (no, I'm not kidding) and filling the tank with water 1 gallon at a time until the water level reached the hole for the filler neck (16 gallons). I'm assuming that there is a difference between the buoyancy of water versus gasoline but, I can't say for sure if they differ enough to matter when it comes to the relative approximation that we get from our factory gas gauge. Anyway, after each gallon, I pulled an ohm reading between the sender and the tank. Before starting I checked the position of the fuel pickup to assure that it was nearly bottomed out in the tank, right out of the box there was roughly 1/8" between the "stock" and the bottom of the tank.

I also used a variable resister and wired it in place of the fuel sender to get known ohm readings for various locations on the fuel gauge. I did my best to get exact 1/8 tank measurements. I was sure to let the needle "settle" before taking any measurements (I literally spent 2-3 hours doing this while working on another project, I wanted to make sure that needle was fixed before taking any readings). In the rare occurrence of 2 readings coming out exactly the same, the results are listed on the same line.

Here are my results;

Gauge	Gallons	Ohms	Notes
	0	80.2	Bottom of sender travel
	1	80.2	Touching pickup
	2	79.6	Mid pickup
E	3	70.1	Above pickup
	4	63.7
	5	58.2
	6	53.7
	7	49.3
1/8		46.0
	8	45.7
	9	42.0
1/4		40.4
	10	37.2
	11	38.1	Erroneous reading? 33.3? Didn't notice until it was to late to recheck or investigate.
	12	29.4
3/8		27.2
	13	26.8
	14	25.3
	15	25.3	Accurate reading, tested multiple times. Large flat taper in the tank at this point.
1/2		24.0	EXACTLY the number that I expected based on my research.
	16	23.7
5/8		19.7
3/4		17.0
7/8		13.6
F		12.4
		10.6	Top of sender travel

I'm not sure if there is much new information here. Due to the amount of information that I read prior to doing the tests none of the results are surprising, more validation than anything else. Still, it's nice to have verified exactly how the readings on the bottom 1/2 of the gauge correlate to the amount of fuel still in the tank.

[green69rt]

So,does you reading say that the sender reads 1/2 full with 15-16 gals in it?   Is that tank 19 gal?

[rebby]

Yeah, according to what I found, there is nearly 16 gallons in the tank when the gauge reads 1/2. Standard 19 gallon tank. I wish that I would have been able to replicate the test in the car. I'm really curious how much the tank really holds and how close to full capacity you can get with the filler tube in place.

[myk]

So,does you reading say that the sender reads 1/2 full with 15-16 gals in it?   Is that tank 19 gal?

That would explain why I've got fuel overflowing out of my filler tube when the gauge is only 1/2 full...

[303 Mopar]

So,does you reading say that the sender reads 1/2 full with 15-16 gals in it?   Is that tank 19 gal?

That would explain why I've got fuel overflowing out of my filler tube when the gauge is only 1/2 full...

I had this happen to me last weekend at a car show.  Fuel running out the vent tube down the frame rail on to the ground under my car.  My gauge read just about 3/4 full.  Has any one ran their car empty to see what the gauge shows?  Well past empty?

[Brock Lee]

Those numbers look like they may be showing an Inverse Log taper to the resistor with the 14-15 gallon area being the offset bend in the graph you see.

I think the originals are a standard Log taper with that bend in the opposite end. Allowing the travel to move slower on the smaller volume area of the tank, and faster in the larger volume area where it takes more fluid to move the float.

[b5blue]

I wonder how much "rake" effects these readings? If the front end is lower it would change the volume the gauge reads to higher I think? Just yesterday I put 6.85 gal. in my 70. (20.00) It was right on E and went to about the correct position part of the way above 1/4.

[66FBCharger]

So it appears the Kramer sending unit is no better than other reproduction sending units?

[poppa]

So it appears the Kramer sending unit is no better than other reproduction sending units?

Not mine at least. Will screw around with this AGAIN in the next couple weeks. In the meantime...here's a happy ending

http://www.dodgecharger.com/forum/index.php/topic,57971.0.html

[b5blue]

I don't fill up ever, in 20 years. (Mostly dead weight.) With a tank/lines change in the future, when I do exhaust I'm saving my Kramer sender till then. I want to check calibration at that time so have no feed back till then. 

[b5blue]

I'm using this Ohm info to program my MeterMatch adapter unit. I'll report back on results. ( https://www.technoversions.com/MeterMatch.html )  My sender is from Kramer also. With about 20 ohm spacing (0-80 ohm full to empty.) I ordered some 20 ohm resistors and will run in series to give 80-60-40-20-0 for E 1/4  1/2  3/4  Full gauge readings.