• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

How to test and adjust a fuel gauge

Share this page

That is awsome Jack! the definitive word, I would say! Did you test and set yours? How does it work?
 
Not yet. Been working on a few other things to get it driveable.
 
Careful, there are at least 2 styles of fuel gauges on Spridgets. I know the early wont work with the later sender, and vice versa. I'm not certain whether Barney's MGA is the same type as Bugeye or as later Spridgets.

If pressed I could get more details.
 
Peter, that gauge is the early unstabilised one. Induction coils and a gimballed movement. The stabilised one is a bi-metal affair.
 
Beleive me, that is a Bugeye gauge. Mine has all those parts, hehe.

Now if I can just get it figured out. Think I will need some resistors, Radio Shack??
 
Cool article.

You should be able to get those resistors at Radio Shack no prob.
 
Next time I am up town I will do so. I am just persistant enough to fight it through.

Look how the case also needs to be grounded for the gauge to work properly, intresting.
 
I have the later model, but I calibrated mine the old fashioned way. filled the tank adjusted for full. took half out of the tank, adjusted. took all out but about 1/2 gallon adjusted for empty. I kept pouring gas in and taking it out and playing with the zero and span until I got it where I thought it ought to be.
 
DrEntropy said:
Peter, that gauge is the early unstabilised one. Induction coils and a gimballed movement. The stabilised one is a bi-metal affair.
Click to expand...

OK... then tell me about the "stabilized" one I have in my Mini..... never reads anything. How to test?

Peter
 
Man Peter, you ask some hard questions. I just found this with help this morning and now you want to know about stabilized ones. Tis my understanding the stabilizer supplys 10 volts rather than 12, shrug. Suspect it might be about the same.
 
If its a mini just give it a roll. I was in two mini rollovers in the UK. The last one was in a round a bout that had black ice in it. Three of us in it and it rolled over. We rolled it back and the top was a mess but the gas gauge worked and it had never worked until then. Week later that one was at the bone yard cause the windshield was coming out /bcforum/images/%%GRAEMLIN_URL%%/lol.gif
 
For what it's worth, below is a copy of my project notebook comparing the resistances I measured from the Bugeye fuel gauge to the MGA. I don't remember how I determined that the sender resistance was 0 to 90 ohms; probably measured 90 ohms when the tank was full and assumed it would be zero, like the MGA, when empty. So, take it with a grain of salt.

If you use resistors to cal the gauge, remember a couple things. First, you should get 1-watt resistors, because that's about how much power will be dissipated in them. Half watt (and smaller) are easier to find, but might get stunningly hot or even burn out. Second, resistors are available only in standard values. Some 'standard' values are not commonly encountered, though. So, assuming that the sender is linear (a BIG assumption), you want the closest standard values to 22.5, 45, and 67.5 ohms. These are 22, 47, and 68 ohms, and should be available at Radio Shack. Again, check the resistance of your sending unit to be sure I'm right on the 0-90 number.

I do wonder why LBCs all seem to use this funny arrangement of three coils instead of a simple, one-coil meter movement for the fuel gauge. I suspect it is some clever way to make it less sensitive to the system voltage, which, as we know, varies a lot. But it can't be perfect, since later cars have that profoundly bizarre bimetallic voltage stabilizer, which, I suspect, works about as well as high-heeled sneakers.
 
The early non-stabilized gauges are easy to identify as the DR mentioned above. They are "fast acting" when any resistance changes happen, the bimetallic ones respond SLOWLY. I'm sure there were different ranges used on the non-stabilized gauges, but every one I've seen was set up to work with senders that operated from 0 Ohms empty to 90 Ohms full. This is also the range used with a lot of GM sending units from the 1960s.

The stabilized gauges operate at 10V as mentioned above and the fuel sending unit operates in the opposite direction with a wider range. The typical, nominal range is 240 Ohms empty to 33 Ohms full.

Peter, to test your gauge and it's sender is fairly simple. Rather than repeat all the steps here, download my PDF on the stabilizer. It has troubleshooting steps in it.
https://home.mindspring.com/~purlawson/files/SmithsVoltageStabilizer.pdf

If your gauge is the non-stabilized type (on Minis your car would be built before September 1964), you'll find additional information relative to that system on the MGA Guru link at the start of this thread. PM me if you need additional help.

EDIT:
Sarastro, the non-stabilized systems weren't unique to the LBC world. They were on a lot of US cars prior to the 1960s. As you suggest, the bridge arrangement was fairly immune to variations in the car's operating voltage. They do bounce around a lot though and calibrating them is a little touchy.
 
Boy is that a nice write up.
 
Beautiful, Doug.... I think your test is .. shall we say, less "intrusive", than Kim's!

We're supposed to get above freezing this weekend, so I might revisit the gauge. The stick and spare gallon routine gets old. I do have a stabilizer, and have looked and tested stuff back there, but there is evidence of some smoke having leaked at some point in the past.

Thanks again. Peter
 
That durn smoke again. We gona need a fix for that.
 
Just got back here and caught up. Thanks again Doug, for your article. And again: It's the best written gauge document I've seen. Anyone fussing with Smiths instruments needs to have it on-hand. Ya oughta get "royalties"! /bcforum/images/%%GRAEMLIN_URL%%/cheers.gif
 
Thanks all. If you didn't notice... I like gauges. I think the best document out there is the one written by Anthony Rhodes on the Jaeger and Smiths speedometers. For the early gauges and electrics, the MGA Guru site is the best I've seen.
 
I've got this thread bookmarked. Lots of good info here, and I've got all sorts of gauge work to do this year (Tunebug's only working gauge is the oil/water gauge). It's not too expensive, and I can do it inside the warm house!

Of course, like always, I've got very little idea what I'm doing, but at least y'all do and I can sponge up the knowledge. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
Back
Top