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MG MGB Technical - Petrol tank sender

I have just got a new sender unit from Moss. This has 3 terminals, 1 of which is shrouded, so I guess that might be for a low warning light.
There is no obvious way round the wires go onto the sender.

Anyone fitted one of these new units?

Colin
Colin Parkinson

Yes the third terminal is for a low fuel warning light, it has been the bottom one with a sleeve from Moss in the past.

Put an ohmmeter between the other two to test it before fitting. It should go smoothly from about 20 ohms to 250 ohms for the locking-ring type, although the lower resistance does seem to vary between examples.

Prior to 1977 models there should be two wires in the harness - green/black and black. The black wire has had an undersized spade in my experience, but these plastic senders may have all three spades the same size, you you have to replace the spade connector on the black wire. I use crimp spades but still choose to solder them, and assemble with Vaseline or similar as this is in a bad place for corrosion. The earth is normally the middle spade, but it doesn't matter with these plastic bodies when you don't use the 'low fuel' terminal

77 and later only have one wire so with the plastic body there is a black wire on the middle spade that has to be bolted to an earth nearby, that needs to be clean.
paulh4

Cheers Paul that was all I needed!

Colin
Colin Parkinson

Colin
I would be interested to hear of your comments on accuracy when installed.
thanks
G
Graham Moore

From what people have reported the new ones seem as variable as the old, which seems strange, anything from 6 to 20 ohms at full although closer when empty. It's easy to recalibrate the gauge to suit the sender - I've had to do that on three out of four OE (i.e. not plastic) replacements on two cars - and any gauge may have been altered in the past to suit the sender fitted at the time.
paulh4

Paul for your info, I took the sender out and checked resistance. It goes from 18 - 185 ohms.

And it will be a while before it gets petrol in, but I will fill in 5litre increments and check gauge at that time.

Colin
Colin Parkinson

Thanks Colin, that's hugely different at the 'empty' end compared to the others, and I'd expect that to show a couple of gallons when you ran out!

But if there is no fuel in yet have you turned on the ignition to see where the gauge points? Or was there some left in?
paulh4

Paul this one is a total new build, dash not in, and no fuel in the tank yet.

It will be a while......

Colin
Colin Parkinson

Take your time :o)
paulh4

Mine was same as Mr Beswick's. To the Ohm!

6 full, 251 empty.

They say a stopped clock is right twice a day, but despite trying to recalibrate gauge at each end, my new sender is WAY out for any volume of fuel in the tank. It's plain crap. I am now resorting to setting my trip meter every time i fill up and i can tell you i am livid. It's the MGOC solid-state super-accurate one.

But it sounds like you may have a different version Colin. Would you pls post a link to the one you have.

Thanks, G

Graham Moore

Graham, it was just the one supplied by Moss, not sure if that is the same as MGOC one.

Colin
Colin Parkinson

The solid state voltage stabilizers will cause fuel (and temp) gauges to read high. I calibrated my fuel gauge to "F" with a full tank by trimming the voltage with an adjustable regulator wired in series with the solid state replacement regulator. The temperature gauge no longer reads above "N" when the thermostat opens and 1/2 a tank is really half full (half empty?)

The bi-metal stabilizers are no longer available so the circuit needs to be fine tuned when a replacement solid state stabilizer is in place.
Glenn Mallory

They have been around for years now and I've never heard of that before. Maybe you got a faulty one, have you measured the output voltage? Should be about 10v.

I take it the case has a good earth? Without that both types will read high. Easy to check - turn on the ignition and let the fuel gauge stabilise. Then start the engine and with the alternator or dynamo charging the fuel gauge should read exactly the same. If it goes higher the stabiliser is not earthed or faulty.

Could also be that the gauges were adjusted to cope with the previous faulty stabiliser.

Full and half are largely irrelevant as far as the fuel gauge goes, what's far more important is what it is showing when you run out. On three replacement senders out of four I've had to recalibrate the gauges, the first two (one car each) still showed nearly 1/4 tank when they ran out. I recalibrated to show E when I had put a gallon back, as something of a 'reserve'. They were all original wire-would senders, but the new ceramic type seem to be just as variable from the resistance measurements various people have taken.
paulh4

My Cousin has had his K reg ‘B’ for over 40 years and I’ve done most of the work on it over the years- it’s not really moved in the last approx 7 years and now the fuel gauge is stuck on half full as it was when last driven.
Any chance it will free off when driven on our smooth rural roads or is it best to pull it and replace it ?
I’m currently about 70 miles from the car so can’t check - can the sender in the end of the tank be removed in situ or is it a tank drop job - I will change the seal and lock ring if I need to replace it.
I fitted the tank 20 years ago!

Richard.
richard b

Rich,
the sender is on the side of the tank so far easier than with our Spridgets. Obviously you'll want the fuel below the level of the sender so empty by driving or look for high kerb, axle stand or ramp. You might cause less disturbance of the sender if you use some sort of three-legged tool rather than drift and mallet.

However if you are able to search out some uneven roads I'd given that a go for a couple of refills or tankfuls. If you need potholed roads we have some in Northamptonshire despite our local MP being loyal to the last and current PM and supposedly getting £2m to locally repair them.



Nigel Atkins

Possible, but it could be the wiper has got tangled up in the windings in which case it will need to be replaced. I assume it drops past E with the ignition off? If not then the gauge is the problem.

If the sender it can be changed in-situ, run it down to about a 1/4 tank (I'll leave you to determine that! Maybe remove the filler hose from the tank and dip it) and raise the right rear corner.

The locking ring has three tapered sections (A below) that fit under tabs on the tank (D). There was a tool originally, I've made my own, but if you work round the three tabs on the ring (C) bit by bit with a light hammer and drift it should come undone anti-clockwise.

I'd advise getting a new sealing ring, but if the existing one comes off cleanly and is sound I'd reuse it as rubber these days is rubbish. This goes between the sender and the tank.

The sender has a cutout on one edge that only allows it to fit properly in one position.

D are recesses on the ring that allow it to go past the tabs on the tank when fitting the ring, then tap tabs C bit by bit clockwise to lock it.

However before fitting a new sender connect the wires to the terminals and make sure it works. You will almost certainly get one of the new plastic ones, these seem to have three terminals and the third is for a low-fuel light which MGBs don't have. That's insulated on ones I have seen from Moss, but there is another issue and that is the two remaining spades are standard-sized, whereas on the original senders the 'live' terminal is standard and the earth terminal is smaller. In which case you will have to fit a standard-sized spade connector to the black earth wire.



paulh4

Thanks Paul and Nigel, glad I now know about the connector change in advance as if I’m 70 miles away from base and snookered for a connector I would not be best pleased !

Richard.
richard b

I fitted a gadget called a Gauge Wizard to my MGA and I used it to accurately calibrate the gauge to the sender unit so that it is now totally accurate.
The gauge shows full when the tank is full and similarly down through 3/4 1/2 full.
Then at 1/4 full level Gauge Wizard can be set to illuminate an led light which begins to flash when the level reaches 1/8 of a tank full.

I have checked this by draining the tank at the 1/8 full warning light point and I measured this at exactly 1 and 1/4 gallons, which with a 10 gallon tank is absolutely spot on.

The beauty of the Gauge Wizard is that, so long as your existing fuel is working, no matter how poorly, it can still be used to calibrate your system to be really accurate.

The calibration process involves draining your tank and then refilling it in 1/4 tank steps. You calibrate the Gauge Wizard at each step and that's it.

I have never had such an accurate fuel gauge and it is great to know that what you see on the fuel gauge is actually exactly what you have in the tank.

Colyn

PS I have my own transcribed setting up instructions for an MGB Gauge Wizard if anyone would like one.

Colyn Firth

Someone gave me a Gauge Wizard to fit to an early MGB as there was an intermediate tank and sender for a short period and the senders for those are not available. That was to reverse the action of the later sender to match what the early gauge needed, which operates in reverse electrically. In the end he never asked me to fit it so it's still lurking on my bench

I did mean to say about calibration. Having had four replacement senders on two cars in quick succession the first was way out and stranded me when it was still showing almost 1/4 tank. I recalibrated the gauge which is relatively easy, and the next two senders also needed to gauge to be recalibrated. Only the final one didn't, so they were pretty variable. One would hope that the new senders would be more accurate as they generate the resistance using different physical components which in theory should be more consistent as well as more accurate. But from what people have written on a forum elsewhere about the upper and lower resistance measurements they seem to be just as inconsistent, let along accurate through the range. You also don't know how the gauge might have been adjusted previously.

Personally E is the most important - I ran mine out, added a gallon back in, then adjusted the gauge for E to give me something of a reserve. F is irrelevant, but for niceties sake you can fill up and adjust that one first, then E, as adjusting one end probably has a small effect on the other.
paulh4

The beauty of the Gauge-Wizard is that you just don't need to worry too much about how inaccurate your present sender and gauge are.
So long as there is some movement of the needle between full and empty, then you can calibrate it using the G/W to make it work absolutely accurately.

Someone I know with a 77 mgb roadster fitted a G/W unit as his fuel gauge never dropped below 1/4 full, even when the tank was empty.
However, he has opted to use the "Pre-set" MGB setting on the G/W rather than calibrate it in 1/4 tank fulls like I did. This hasn't really improved things very much and the gauge still doesn't drop below 1/4.

So if you do buy a G/W, it probably won't improve matters unless you calibrate it by filling the tank in 1/4 steps.

Cheers
Colyn
Colyn Firth

I had the wildly inaccurate gauge problem when I first built my GTV8. I used new white faced gauges from Speedy Cables and a standard MGB sender. The gauge showed full when the tank was full, but showed empty way too soon, when the tank was only half drained.

I found that the sender went from 300 ohms at empty, to 30 ohms at full, whereas the gauge required the same 30 ohms at full, but only about 130 ohms when empty.

My clever son constructed an Excel spreadsheet in which I could input a resistance value to add to the sender resistance (1/R + 1/R) to see what effect it would have across the range. It seemed that if I fixed a 220 ohm resistor across the terminals on the back of the gauge it would be more or less right, and so it has proved over more than 10 years use.
Mike Howlett

Found one of the original metal senders on E bay - says it a Smith’s - see if it’s any good when I get around to fitting it - all too cold for me at the moment !
richard b

Before fitting don't forget to connect it up and check the float arm move smoothly up and down, and it goes to F and E!
paulh4

I returned the sender i bought from MGOC. Showed them the readings which were just sooo way out.

not had any problems on the other 2000 we have sold....

then 10 mins later...we had a faulty batch when you bought yours...

whatever...

I bought a new one (old Smiths style) from Ron Leacy who is setting up shop again having sold Leacy classics. he assured me it was going to be accurate, and it was.

But I did have to recalibrate and without a variable power supply which I have on my bench, I would not have had a hope.

I filled the tank 1 gallon at a time and read sender resistance and gauge volts, so on the bench i could recreate all readings even after changing the calibration points. The think is that if you have to change 1 end quite a bit (F or E), it changes all the way to the other side of the half mark.

So at last, I am happy. Ecstatically so. I have a sender/gauge that reads correctly and consistently at all levels. Only took me about 50 hours start to finish but every time I looked at the inaccurate gauge, having fitted new tank etc, it made me very unhappy.

G
Graham Moore

50 hours? Really? When the only important setting is E and to some extent F?

I assume you used a Gauge Wizard? If not I don't see how you could get it accurate at more than two points, set by the adjusters on the gauge itself.

I've been over to Leacy's a few times since he apparently sold it and haven't noticed any difference.
paulh4

“not had any problems on the other 2000 we have sold....”

If only I had £1 for every time I’ve heard that.

“...Ron Leacy who is setting up shop again having sold Leacy classics.”

Really? Under what name and where?

I didn t realise Leacy Classics had been sold. I was reading only the other day, that they had taken over X-part.
Dave O'Neill 2

He has opened an ebay presence trading as
traditionaloldmotorspares

Yes Paul, about 50 hours - including tank change. Stacking CD's to simulate gallons of fuel, recording data, playing back scenarios using a variable power supply. change calibration and do it again until finally (see pic)
i forgot to get pic of 1 gall, which I set at E by design. but the others are in 1 gallon increments left to R top to bottom.

G




Graham Moore

Lol Graham
That's a fantastic pic. I love it
You could just stick that on the dash and pick one
Worth 100 hours just to get a result like that
AND -good idea having a gallon up your sleeve at empty
By the way, just a question --curious
When you go to buy fuel at a servo over there, is it still sold in gallons, or litres
Cheers
willy
William Revit

Fuel is sold in litres over here Willy.

Having a gallon in "reserve" would bug me - no idea when is it actually empty, "oh it's OK, there's another gallon in there" - until it stops!

I am with Paul, get empty spot on, the rest doesn't matter, I always refuel when it gets to 1/4 and carry the gallon in a spare can - that way you KNOW there is a gallon available at all times!
Chris at Octarine Services

Cheers Chris
Everyone was talking gallons, it had me wondering
William Revit

Willy,
although some petrol pumps were displaying in litres from so long ago that no ones seems to remember or agree, it goes back decades.

However most in our generation will still think of gallons and convert from litres to gallons to work out mpg (miles per gallon) to give an idea of how the car is running.

If you say the car's doing 25-28 mpg others can make a judgement but if you say 5.5-6.2 miles per litre or worst still 8.8-9.9 litres per kilometer it'd be meaningless without a calculator and conversion tables (I hope I've got the figures right).

Then of course you have the US gallon . . .
Nigel Atkins

miles per litre is a bit weird
The normal way to express fuel useage is litres/100Klm
As in 5lt/100K if you have a Golf or probably 10 for most cars
William Revit

Most people in the UK talk in miles per gallon, or how much they spend on fuel every week. As said before, I reset the trip at fill up, and refill every 200 miles, or sooner.

In light of the foregoing conversation it'll be interesting to see what what readings I get off new plastic sender (being replaced along with tank today). Old tank had classic perforation along top offside, also rusting out boot floor directly above.

Not going off on too much of a tangent, but does everybody nowadays just fill up, rather than putting in, say, £20 worth? Would this be a function of paying for fuel by debit/credit card, rather than cash?
Peter Allen

Yep, always fill the tank on all my cars. My dad always put four gallons in his car no matter how empty the tank was. Strange when you think about it. I suppose four gallons cost about one pound back then.

Willy, here in the UK we made a half-hearted attempt at metrication back in the seventies. So petrol sells in litres, but everyone, even young people think in terms of miles per gallon, and those are the figures published in motoring publications. Beer is still sold in pints, as is most milk. We still think of our body weight in stones and pounds not kg.

We're an odd lot.
Mike Howlett

Interesting mixture of measures Mike
We changed over to dollars and cents from pounds in 1966 so I was just lucky, went through school with pounds and shillings etc and 1st year at work was dollars and cents-couldn't have worked out better
Australia then went through a metrication period and in July 1974 we went 100% metric--made life a lot easier rather than trying to convert all the time-I haven't heard of anyone talking miles / gallon for years, except on here
Our dollar notes here go-5 10 20 50 100
It's roughly $2 to one of your pounds
I usually poke $50 of diesel in my golf each time which at current prices is 32 litres and get 800klm out of that---4lt/100kl
What price is your diesel there, it's $1-56/lt here

Everyone weighs in Kg, haven't heard of stones and rocks for decades
Interesting though, digging in the garden here a while back and found an enamel sign from, I guess, a postoffice vending machine--it says insert halfpenny in slot and take stamp----bit of a blast from the past
cheers
willy

William Revit

I normally always fill up my midget as the tank combined with the filler neck only hold about 27 litres.

I was taught in junior school in the late 60s metres, centimetres and decimetres (don't hear of those anymore) and the next year I moved school and was taught about yards, feet and inches and chains and furlongs, no wonder I'm so messed up. :)

Willy,
stones and pounds here.

When we "went metric" you would buy wood say like planed 19mm x 19mm - in 6 foot lengths!

A pint of ale (beer, not lager) I'm told was sold in pints because originally if you asked for beer it could be in any measure but if you asked for a pint of beer then it had to be a pint,now of course we have Weights and Measures laws.

We went to a pub local beer festival a god number of years ago and the very miserable landlord was selling pints in the beer tent in the garden in plastic half-litre 'glasses', a pint is 568ml. When I pointed this out to his more friendly wife serving in the pub building she marched into the tent and made him remove all the plastic half-litre 'glasses', so funny to see his face.
Nigel Atkins

Fill and zero trip.

Tyres here (at least) are in Metric widths and Imperial diameters
paulh4

Willy, 1.56 AUD is about 0.80 UK pounds. I filled up my VW diesel a couple of weeks ago and the pump price was £1.24 a litre, so half as much again as your price. You have cheap fuel! My tank full cost £54.92, nearly 107 AUD. How do you fancy that?
Mike Howlett

Willy,
as long as you don't rely on your German computer working out litres/100Klm!

I'd forgot it was l/100 km - and I'd forgot as Paul put about the tyres, we've been doing these things for so long we don't alway notice, or how strange or stupid they might appear to other or actual are!

To me the metric system makes a lot more sense but for some we still should have "British" things like £sd but when a mate's 30 year old lad said he was 1 metre whatever tall I was lost as I could only think in feet and inches.

Years ago I honestly asked if the 19mmx19mm wood was in 2 or 3m lengths and the guy said without a hint of irony they were 6ft.
Nigel Atkins

And what about that strange thing in the UK where the bore and stroke of an engine is measured in millimetres, as it was in pre-metric days, but when you get a rebore they refer to 20, 40 etc thou of an inch oversize.

There are inconsistencies abroad, too. Of course the Romans referred to miles, and what about that great road race the Mille Miglia. Paul's point on imperial wheel diameters also seems to pertain to Continental cars sold in Europe, and maybe elsewhere.
Peter Allen

Hmm
Don't hear of decimetres at all much
Most measurements are in mils (milimetres) centimetres or meters
People height is --eg.--185 centimetres
timber from the shop would be for example --
19mil x 19mil x 2metres or if your getting it cut off to length you'd ask for 1900 or 1950 or whatever
Just for you Mike I filled the golf up yesterday, ran it down to 20klm to empty (which i hardly ever do) and it cost $77--49 litres
Nigel -have faith my friend--I find the German trip computer quite acurate
Interestinly out the road here is a dead flat straight stretch that follows the edge of the sea, I can go both directions and sit on 4lt/100 but if there's a bit of wind it goes 4.1 against it but back to 3.7 or 8 the other way--you'd think the diff. would be the same as in 3.8-4.2 so it sort of proves there is more advantage in a tail wind than loss in a head wind
William Revit

Willy,

That will be because cars are aerodynamically designed to go forwards rather than backwards ....

Chris at Octarine Services

If you really want to make an imperial/metric mixup you need a rocket scientist

https://www.simscale.com/blog/2017/12/nasa-mars-climate-orbiter-metric/
R.A Davis

"That will be because cars are aerodynamically designed to go forwards rather than backwards ...."

Now that really did make me laugh! Although with a couple of cars - early Porsche Boxster? maybe they were hedging their bets.
paulh4

Willy,
my faith or lack of would depend on whether the VW computer is pre or post emissions cheating. :)
Nigel Atkins

It must be a German thing, I always thought the Karmann Ghia looked like it was going backwards
R.A Davis

Drifting back on subject !
Just tested my replacement (hoping to sort the car tomorrow) 14-265 ohm range with my gauge.

R.
richard b

"Although with a couple of cars - early Porsche Boxster? maybe they were hedging their bets."

Maybe the boat tail MGs too!
Chris at Octarine Services

Nigel
The US dept. that snagged VW for it's emissions forgot to look at their own products
The Mustangs and Comaros with their trapdoor exhaust systems that are designed to pass the drive by noise emissions but go wide open on heavy throttle would have to be an offender
Interestingly ,I had my VW chipped up to 195 HP (UK measurement)145Kw and fuel economy actually improved overall------emissions-? but honestly if it uses less fuel it must be better-yes
The fix for the VW emission thing was a plastic vortex/vane in the airflow meter to get a more accurate reading of what was going through
Ok you win you got me wound up
cheers


Richard
Sounds like you're onto a winner--good luck
I had exactly the same problem with a stuck gauge on my elan after it sat for years ,it was on around 1/4 tank and wouldn't move, tried rough roads , a stick down the filler tube ,bashing the tank and all, nothing worked
Pulled it out and the wiper was stuck to the resistor windings with all this black goop, cleaned it all up with thinners-took a while- and it's been ok since--hope it stays fixed
William Revit

Well my trip to Devon to start the B (only run a couple of times in the last 7 years ?) didn't go exactly to plan !
Tested the gauge by shorting to earth and gauge AOK.Fitting new sender will have to wait.

No delivery of petrol from pump - removed pump and was rather amazed that the 'cork' sealing gasket that fits below the inlet air bottle cover had disintergrated and the bits swollen up and nearly filled the chamber ! ethanol fuel again - they say the new ones are 'resistant'. cleaned and tested and ran well.

Angled pipe connection into tank seemed to have lots of black gunge in it and blocked filter into tank. Using an old foot pump I managed to blow it back into the tank and after a while seemed clear but I think the tank will have to be dropped to clean it out if possible - is the angled connection on the tank removable ?

Finally got fuel to carbs and it started virually right away but the carbs need stripping as the fuel needle on one is sticky and leaking - good to hear the old girl roar again !

Lots of work ahead !

Thanks for info on the sender testing etc.

R.
richard b

"ethanol fuel again"

If it's not moved for seven years I doubt it even if you are unfortunate to have E10 by you now. More likely it dried out and broke up. You only have to think how many tens of thousands round the world have been using E5 and higher for years without a problem like that.

You are likely to have more of a problem with new gaskets depending on where they are from. SU Burlen told a pal that some parts changed but they didn't give them a different part number, and end up being incompatible. What started off as a simple points clean and adjust for him ended up as a new pump because he was foolish enough to remove the air bottle and damper covers and replace the gaskets and seals.
paulh4

Can anybody confirm if the 90deg elbow into the tank is removable i.e screwed in ?
I'm assuming the tank filter cannot be removed either ?

R.
richard b

This is a pic I shot during a Heritage visit of them making MGB tanks but I seem to remember them saying thet were for racing or something hence the additional baffles ?

This looks like the elbow might be removable ?

R


richard b

If you look at the tank in the background, you can see where it’s been heated around the elbow, so probably welded or brazed in.

My original tank has internal baffles, whereas the replacement that I bought, but didn’t use, hasn’t.
Dave O'Neill 2

This thread was discussed between 13/11/2019 and 14/03/2020

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