Fuel Gauge Accuracy

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
The only time I ever saw a Rover fuel gauge that was accurate was in the Defender, when it had it's original tank, sender, and gauge. Even when I switched the gauge to VDO, it was pretty accurate once it got past the first 70-90 miles. I think the RRC gauges were just as bad as the Disco gauges -- even my 2004 Disco pegged to the top, and wouldn't start moving till it got past 70 miles, then it was relatively accurate all the way down.

Now that I have a new tank, sender, and gauge, I really have very badly skewed gauge readings. It won't come alive till I've driven 100 miles, and I have no idea how much is in the tank anywhere above half way. If the needle is at half way, I think I may have anywhere from 10-13 gallons used. And my fuel light did work at 2 gallons in the tank, but I'm not sure it is working anymore.... it works fine for 30 years... then when I get a new tank and sender and such, it decides to stop working just one month later...

When I put the tank in, I verified that the 1/4 mark really was 5 gallons, but then when I fill it up from 1/4 tank, it often needs 18 gallons to fill, sometimes 13, sometimes 15.

So, how can I adjust to make it read more accurately?

I know that if I slightly bend the sender float arm I could at least make it accurate (theoretically) for the first 3/4 of the tank. But I imagine that once it gets down low, maybe that light would never come on, and the low fuel indication would be inaccurate as much as the high fuel level indication was inaccurate. And there isn't any precision in trying to figure out exactly how much of a bend is needed!

I thought maybe I could put a resistor in the line someplace. But this is only my brain trying to think through the way electrics work, and I wouldn't know where to put it, or how much resistance to add.

Any other ideas?
 

Red90

Well-known member
Senders can't work when a tank is full. It is just simple geometry. The level needs to drop lower than the diameter of the float before it can move. Every fuel sender works this way.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Yes, but I'm wondering if there is a way to get it to come alive sooner -- before I've used five gallons, for instance. That's 3/4 of the tank, plus or minus a gallon if they topped it off into the filler neck. But mainly, I want to be accurate at the 3/4, 1/2, and 1/4 marks.
 

Napalm00

Well-known member
Sounds like your arm may just need some adjustment. My sender is aftermarket (3rd one) with a VDO gauge and it works great. If you totally fill the tank you need to wait until the level drops below the arm to get a reading other than 100% full as Red states. There is no way in making it read earlier
 

Red90

Well-known member
If you have it adjusted (the arm) to read where you want for the bottom range, the top will be what it is. There is nothing you can do to change the span. If your low fuel light is not working, you have a bad sender or bad wiring (I'm assuming this is a pre-91 truck)
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Yeah, it's 1988. I did the tank and sender in ...December, I think, and the light worked then; tested at 2 gallons or so. And it came on while driving a few times over the past few months, but seems to have stopped working.

Anyway, I get that the float will be pushed to the top of the tank, but it seem to me that once you use about 2 gallons, you should start seeing it move. In other words, it seems as if the top part of the sender contacts are all pegging the gauge, that the demarkation from one contact point to the next is not extensive enough to produce any kind of reading until I'm 100 miles/5 gallons into the tank. By then, the float should be down off the roof enough to be registering on the gauge. (And the gauge is sensitive, the needle does "bounce" in particular situations when sloshing on a hill at, or below half tank.)

So bending the arm is an option, as you said, for the lower 3/4 of the tank, maybe? But still would not fix the top end.
 

pmatusov

Founding Member
Just an observation: the RRC/D1 fuel gauges in my experience had insanely good consistency.
In three Classics and two D1s they would show exactly the same: from the up-the-wazoo-top-off,
- top of the scale (100%) would show at 45-60 miles since the top-off,
- 3/4 tank would register between 90 and 100 miles,
- 1/2 tank would actually be 11 gallons left (out of nominally 23.6)
- 1/4 tank would be 6 gallons left
- the light would come on with about 2 gallons left.
As much as I would love to have an honest and linear fuel gauge, I've resigned to accept these numbers.
And keep a full 5-gallon can in the truck.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
With the Discos, and especially the 2004, I would agree.

I guess I'm just annoyed that the truck used to have a very accurate gauge that was consistent with every fill-up, and now that I have all new equipment in the fuel system, it seems to not make much sense. I'll make a point of filling it up when the gauge shows exactly half full. The last time I did this it took 13 gallons.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
LOL! it is a pretty flimsy piece of kit.

Other than just ...bending it, is there anything to adjust?
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
For instance, right now I'm at just a hair below 3/4 of a tank. This would seem to be saying that I've used about 5-5.5 gallons. However, using the maths, and my average MPG, I have actually used 9.5 gallons from this tank so far. Technically, I should be just a bit away from 1/2 tank showing on the gauge. Another way to look at it is to say that my gauge has only 75% accuracy.
 

rocky

Well-known member
On my 90 it's amazing how big a swing in the gauge I get when I go around corners. Right turns lower, left turns higher.
 
Top