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MG MGA - New fuel tank sender unit.

Partially from desperation I have taken a chance and ordered a new fuel sender unit from NTG (mgbits.com).
I have run out of fuel twice over the last 12 months, mostly because I was foolish enough to take notice of my fuel level gauge!

My gauge shows "Full" when the tank is full but it rapidly drops to "Half-full" and stays there, even when the engine stops as the fuel runs out.
(I normally zero the trip and begin to look for a fuel station when it shows 200 miles.)

Well the sender unit arrived today and, naturally, I took it into my workshop and tested it using an accurate ohmmeter.

To be honest I was amazed to see that it's range was 0.5 ohms to 72 ohms. This is almost exactly the same as Barneys recommended 0 to 70 ohms!

So I am hopeful that it will actually work as it is supposed to.

So the next thing is to temporarily wire it up to the sender wire on the tank and see if manually moving the float will move the gauges needle between empty and full.

I will let you all know if it works as soon as I have tested it.
Then there is the fun and games in trying to stop it leaking fuel past the gasket.

To be continued😊!

Colyn




Colyn Firth

Many years ago, I elected to refurbish my sender unit because the new ones were poorly made. The number of windings were few and loose. Why bother making it?

As for the gasket, I think I resorted the original gasket rather than a fuel resistant rubber one. I still had fuel drips coming from the bottom where the wire screws on. I found some sort of sealant goo that worked.

When my gauge read "Empty," it truly meant empty. Before reinstalling the sender unit, I bent the float arm slightly to provide me with a perceived, virtual indication of a fuel reserve; i.e., when the gauge read Empty, I really had an extra gallon in the tank.
Arthur DiLello

Colyn
I replaced mine earlier this year. Do you have the super improved rubber gasket? http://www.mg-parts.co.uk/index.php?route=product/product&path=164&product_id=213

Pretty expensive but not if it makes the job easy. Mine was included when I bought the sender from Brown & Gammon.

This may be useful if you havent read it already https://www.ukmgparts.com/userfiles/pdfs/ahh5114.pdf

Graham
Graham V

Mine came with the standard cork gasket Graham, my present gasket is cork and seems to be ok if I use hylomar gasket seal on it.

If it doesnt seal I will try your rubber gasket.

Im going to fit the sender next week after the run to MGA Day, otherwise I can forsee a 130 mile trail of petrol behind me just waiting for a spark!

Colyn
Colyn Firth

My new Moss tank sealed fine first time using cork gasket an nylon washers. I didn't use the rubber one I had purchased as screws that came with it wouldn't fit the tank and the standard screws are too short for the rubber gasket but all fine.

Paul
Paul Dean

Colyn, I used Hylomar sealant on the gasket to tank, gasket to sender and on the threads of the screws on installation. No Leaks. Sealing machine screw threads with the Hylomar worked brilliantly.
... CR
C.R. Tyrell

Colyn

Sorry, I can't let this one go! Another use for the luggage rack. Should be good for the 130 miles you are talking about.

Steve


Steve Gyles

Yes although I didn't need to use hylomar this time I have use it successfully in the past. BUT be very careful to be sparing as if it gets in the tank all hell can let loose. I guess you can feel the scars from past experience.

Paul
Paul Dean

Steve, now that you have converted your car into the Worlds only MGA Petrol Tanker and almost doubling its fuel capacity , well Im sure you will now be happy to gift me your redundant fuel sender unit! :-)

With that much fuel on board Im certain that you will never ever need to look at your fuel gauge again!

I would have thought that with your supersonic background you would have gone for a more streamlined drop tank design :)

Colyn


Colyn Firth

Colyn

I've another 4 in the attic all bequeathed to me by my late Father-in-Law from his Morgan 3 Wheeler days.

Back to the topic. Still on my original sender but I used the rubber seal and supplied bolts and washers with my new Moss tank. I use Wellseal. Lovely sticky stuff, can just about spread it with an artist's thick brush. Swear by it.

Steve
Steve Gyles

Paul,
yes I have had a similar experience after a well meaning DPO had used some clear silicon sealant in and around the fuel tank.

This resulted in a six month battle with a mystery breakdown where the engine would run great for 15 minutes and then develop a gradual misfire which would worsen until the engine stopped.
After about 20 minutes or so of fiddling with plugs, leads, points, etc the car would always restart and run again for about 15 minutes after which the misfire would return again as before.

It took months of changing distributors, coils, leads, plugs, points, condensers, I even soldered up all the points and condenser wires.
Nothing worked until I got Bob West and James on the job and they found that the front float chamber was empty!
It turned out to be a piece of clear silicone sealant that was invisible inside the glass fuel filter. (The silicone had been partially dissolved by the unleaded fuel)
This gradually floated over the filter outlet and blocked it, then when the pump was switched off, the silicone fell down to the bottom of the filter and the fuel would flow again.
It almost resulted on me giving up on the car altogether.

I had to check the filter every month or two to remove more silicone and it was only really solved when the stainless steel fuel tank had to be replaced a couple of years ago when it rusted through! (Thats another story!)

So no silcone sealant anywhere near the fuel system for me.

Colyn
Colyn Firth

Just a final update on this thead as I have finally fitted the new sender unit.
( I have already brought this up on another fuel gauge / sender unit thread and then realised that I should really do a final update on this one)

I tested the sender unit by doing a temporary connection to the gauge and turned the float arm through its arc.
In the fully down position the gauge showed on empty. In the fully up position it showed about 1/8" below full.

So a week or so later I had the car on jacks to change the rear drums and shoes and I decided to tackle the sender swap.

The tank was almost empty and I removed the old unit with no problems.
The new one went on using the new stainless screws and the cork gasket provided, plus a smear of hylomar on both faces. ( and no leaks-so far!)

With tank full the gauge shows a fraction under full but when I ran the car down to empty on the gauge, refilling proved that I only had about 2 pints remaining.

A couple of refills later I proved that when the gauge indicates that it is down to 1/4 full, there was actually 2 gallons (imperial ) in the tank.

So this is a vast improvement for me and it means that I can at last trust the gauge and not be quite so fixated by the odometer.

Cheers
Colyn

Colyn Firth

Hi Colyn,
I'm pretty new to MGA's but not old motors.
I find I'm doing a lot of reading at the moment as one might expect.

Your post rang a few bells as my car came with a Jaeger fuel gauge that started at almost 'Full' - ran down to about 3/4 and stayed there.

I spent a fair bit of time before discovering that the sender unit was something like 25ohms 250ohms when it needed to be 0 - 75 ohms approx. (I was told the 25 - 250 ohms or thereabouts was the sender from an MGB???) I tried modifying the arm of an old Austin gauge of 5 - 75ohms. That wasn't very successful!
I spoke to an online supplier - very helpful but suggested that the 0 - 75 ohm senders were not available anywhere!

In desperation I've fitted a 'Smiths' gauge that is apparently from an MGB - in light of the fact that the sender unit that came with the car was apparently suited. I now have an (almost) accurate gauge.

As you seem to have obtained a reliable sender - and I would really like my original Jaeger gauge to function, could I ask, was this sender sold as MGA 0 - 70/75 ohms please? You say you were surprised when you measured the resistance.

Regards,
TGee.
T Gee

TGee
I was both surprised and delighted because most I didn't expect the resistance range of the sender coil to be so near to the 0 to 70 ohms range that the gauge needs to work correctly.


My previous gauge (which was bought new some years ago) measured 15 to 98 ohms which is why it showed full most of the time and then quickly dropped to half-full and stayed there until the fuel ran out!

So there must have been a redesign, probably they have now used the correct thickness wire and the correct number of turns on the coil.

But if you buy a new one, check the resistance on an ohmmeter and test wire it on the car before you fit it.

If the resistance range is not very close to 0 -70 ohms, then it is not going to work very accurately and I would send it back for exchange.

Cheers
Colyn
Colyn Firth

Hi Colyn,

Many thanks for the information. I shall have a check with NTG...... sounds promising ;-0
Regards,
T Gee.
T Gee

Colyn gives us data to test if the sender unit is working correctly, very useful. But does Colyn or anyone else have data to test the gauge as well?

Paul
Paul Dean

I bought a sender from Moss and tested the ohms before I installed it. I could not get the correct readings at all. However I used it to plug the hole and hey presto, it worked! Maybe not with accuracy, but pretty repeatable and I know when to fill up.
Art Pearse

Barney has many informative pages and instructions on this page, and the following pages.

http://www.mgaguru.com/mgtech/electric/fg_01.htm

I B Morris

Have you seen Barneys article on this subject Paul?

http://mgaguru.com/mgtech/electric/fg_06.htm

It seems to cover all that stuff.
When you read it you will understand why I never got around to trying this. :-)

Colyn
Colyn Firth

I understand why you never pursued this. In reality I think it might just push to take the sender unit off and check/replace. I have been rather loathed to do this as when I fitted a new super Moss tank earlier this year the standard gasket sealed in one hence my reluctance to disturb it. I did once try to calibrate a gauge well before Barney's article and the gauge finished up in the bin! But I could get a couple of resistors and check it. More later.

Paul
Paul Dean

This thread was discussed between 09/08/2016 and 21/10/2016

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