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MG TD TF 1500 - Fuel Sending Unit

Went in the garage this morning and smelled gas, fuel sending unit is leaking! I'm not fooling with it and will replace it with a new one. My original unit has a Brass float, will it fit on the new ones? I don't want a plastic float. For sealant I use Hylomar AF. PJ
Paul161

From the Frame Up can provide you with a unit with the brass float but you will have to specify that...otherwise you get the plastic job.
MG LaVerne

Paul,
Hylomar is not fuel proof-only fuel resistant. Permatex seems to be the common choice in USA and Reinzoplast in Europe.

Regards
Declan
D Burns

PJ can you determine where the leak is? The terminal, cover plate or the tank screws? Having just restored one I'd be keen to find out exactly where your problem is. Also I'd be interested in suggestions for an out of the car leak test that I could undertake on my unit & the float, prior to final installation. Obviously I don't want to immerse it in water or even petrol but maybe in metho or kero & then hope I don't see any bubbles? Cheers
Peter TD 5801
P Hehir

You need to find the leak, carefully w/o sparks, etc. Could be the unit to tank gasket, the back plate or the terminal stud. Snugging up screws/nut may be all that is needed. IMHO nothing is better that an original unit with the metal float restored with the Abingdon Spares gasket set using Permatex Aviation sealant.
George Butz

Hey Paul and all, having had issues with the sending units on the TD, MGA and TC, here is my current solution to the leaks. First, make sure that the tank surface and, especially the sending unit, are clean and FLAT. On two Moss units I bought, the castings were not flat. A file solved that issue. I than mount the units with dry gaskets, as original, and no leaks appear. Hope this helps, good luck, Tom
Thomas McNamara

One of the things I discovered with my fuel sender unit was that the base plate had deformed. The light metal, combined with a thick gasket, meant that the metal was bent under each bolt, at each bolt hole, giving a "fluted" appearance.
Using an anvil, I lightly tapped it all around with a hammer and a piece of flat steel, until it was visually perfectly flat again, before reinstalling. Then I used gasket sealant and was careful not to overtighten.
P Hehir, I read somewhere that no leak test is sufficient unless you do the boiling water test. My metal float had leaked, so I opened it up with my smallest drill bit, drained it, let it dry for several days, used a match to burn out any remaining vapor (it looked like a little candle for about three minutes before it sputtered out). Then I re-soldered it and then put it in a pot of water and brought it near boiling. As it heated up I could see little bubbles coming from two spots, which I then cleaned and soldered and tested again.
I'm afraid that any test without heat won't create enough pressure to show the tiny leaks that can occur. And obviously, you don't want to try heating it in petrol :)

Geoffrey M Baker

I am with Declan, use Permatex 2 on everything. including around the terminal stud and especially the the threads of the mounting screws. Do not over tighten the mounting screws around the flange. Cast aluminum does cold flow and will deform over time if the mounting screws are over tightened. Cheers - Dave
DW DuBois

So what is being said, that the leak is probably in the gaskets or screws, or both? The unit works fine, so I'll pull it off and check it out. Thanks a bunch! PJ
Paul161

Ok, I just pulled the unit off and found the two top screws had no sealant on them! So I'm cleaning everything up and Moss is sending me new gaskets. Probably didn't leak before as I only had about a couple gallons of fuel in the tank, I filled it yesterday and the fuel went up past the two top screws and the trouble started. Those two top screws are a pain when the tank is on the car. Had to use an angle screw driver, as most of you already know. Thanks to all for the help! PJ
Paul161

I'll undertake the float test Geoff as I have an original unit with the tin can float. I was keen to also test the body of the unit but as I mentioned I don't want to immerse anything but the float in water. In the absence of any other suggestions I'll let it lie in kero for a while & look for any sign of bubbles. Cheers.
Peter TD 5801
P Hehir

My unit has the original tin can float, but it's coated with a cream colored protective coating of some type. Looks good and doesn't leak. PJ
Paul161

Peter, not sure what a liquid test of the body will tell you. The only leak points are the gaskets so you can't test that until its in place. Unless the body has a crack... which only a visual inspection will show you.
The main issues I found with mine were making sure the gaskets were new and well sealed (all 3 of them including the small one for the threaded electrical connection), and making sure the sender unit base was flat, because it can easily deform when overtightened.
On another note, here's the world's handiest tool for working on the sender unit when in place:

Offset reversible ratcheting driver with replaceable heads...

Geoffrey M Baker

PS, just found you can still buy them (mine must be 50 years old from an antique tool store in ME bought 20 years ago)

http://www.amazon.com/Craftsman-9-41469-Reversible-Ratchet-Screwdriver/dp/B007KHEMPA
Geoffrey M Baker

Don't forget the terminal entry point & the contact cover plate Geoff as both of these are possible leak pints, bearing in mind it's inevitable some fuel will enter the body of the sender via the float pivot entry point. These are the other two areas I want to test BEFORE I fit it to the car. If there is a leak I don't want to fill the body with water hence water testing just the float. If I can't see any bubbles when I immerse the body in kero then that should indicate I have no leaks. The last thing I want to have to do is get under & mess about replacing the sender unit.

A point on tightening the tank screws. Partially tighten each screw by moving to either of the two screws furthermost away from the one you were just on. This will help ensure you don't distort the plate. Same principle as tightening the head bolts or the wheel nuts. Cheers
Peter TD 5801
P Hehir

The leaky "pint" is missing an "o". Cheers
Peter TD 5801
P Hehir

I always examine my pints for possible leaks, Peter. I find that somehow, over the course of any given evening, several pints will have leaked completely.
:)
Point takein on the tightening procedure, I did the same.
I suggest using plenty of sealant to help "bed" the unit without overtightening. After I'd rebuilt my sender unit I tried installing without sealant on the principle that they didn't use it initially, and a perfect installation doesn't really need it; but because my sender still probably doesn't have a perfectly flat base I did find a very slight leak at the gasket, so I disassembled and reassembled this time with gasket sealant. No problems since.
Geoffrey M Baker

Having spent time taking the tank off, sloshing it and carefully refitting a new sender unit and sealing it without overtightening the screws...and making sure the surfaces where flat. I now, after a year, have the wretched leak back again.

If I knew a way of blanking the bloody thing off I would gladly do it and forego the sender.

I would use the warning light on the dash for something useful like an indicator.

I never trusted that sender unit and I don't much like the idea of stale fuel being trapped within it.

Has anyone sealed the hole permanently? How did you do it?
Doctor Bob

You could of course just remove the sender and make a blank steel plate. I did the same just to set up a jig to clean out my tank without having water flying everywhere...
But honestly, a blank plate is equally as likely to leak as the sender unit, right?
I suggest you just use plenty of gasket sealant to bed the unit to the tank...
Geoffrey M Baker

Can you confirm where the leak is coming from Bob? Sure it's most likely to be at one or more of the 6 screws securing the unit to the tank, but the 4 screws securing the cover plate or the terminal entry point are also candidates. You may be able to resolve the leak by gently retightening the 6 screws. I doubt the plate is bent or you would have had a leak not long after installation. The other real possibility is the gaskets. Info in the archive indicates some of the rubber ones, including those from Moss, are affected by fuel & then over time they start to leak. Abingdon Spares sell quality sender unit gaskets & they certainly get my vote as I just don't trust any of the other suppliers when it comes to these gaskets. I have both Stag & Permatex 2 & as Stag is thicker I'll be using that on the final installation of both the gaskets & the screws. Cheers
Peter TD 5801
P Hehir

As the Australian product called "Stag" has come up before, in the UK it is called "Wellseal". It is available from Moss USA under the name Wellseal. It is a rather thick sticky adhesive. I use it in conjunction with solid copper head gaskets for a positive leak-proof joint.
Lew3

My TF came with the fuel sender penetration sealed off. A steel disk with holes drilled on the PCD to match the tank was used. An insertion rubber disk fabricated in the same manner was used to seal the tank compressed between the steel disk and the tank.

If you search the Archive for my posts you will find how I finally beat leakage problems when I fitted a sender.
Starting point is to buy gaskets from Doug Pelton, then fit an "O Ring" to the terminal post to seal it correctly.

The quality of the replacement units is shoddy however applying some skill can resolve the issues.

"Stag" is also the only sealant that worked for me, other products that have been mentioned on this forum were not up to the task.
G Evans


I am no longer sure where my leak comes from but to answer your question Peter I suspect it is the Moss gaskets - and yes they were of a rubbery type.

The Moss sender is of poor quality and the surfaces did need flattening before fitting.

Thanks everyone for the tip of using Stag Wellseal - I will try that. I had used another brand of non setting fuel proof sealer whose name escapes me.

I will have one more go of taking the sender off and fitting Abingdon gaskets and sealing everything again including the threaded holes once more but this time with Stag Wellseal.

This is the sender units last chance though. If it leaks again it goes in the bin and I will plug the aperture.


Doctor Bob

Good luck Dr Bob! Don't you just love Moss ... Cheers
Peter TD 5801
P Hehir

The new rubber type gaskets I just got from Moss are Viton. I used Hylomar as a sealant. I'm not sure about the Viton gasket for the sending unit, as it has a tendency to spread out with very little torque on the screws. I have a new cork gasket as original if this Viton setup leaks. If you use Hylomar, make sure you have some lacquer thinner handy, it's the only thing that will wash it off where you don't want it to be. PJ
Paul161

Sometimes I wonder, if you purchase gaskets from Doug Pelton you will find they are molded with a strengthening ring on the outside circumference, this reduces the tendency for the gasket to spread when it is under clamping pressure.

Doug engineers his products so they do not have the same poor characteristics that are sold elsewhere.
G Evans

Graeme I wasn't aware that Doug supplied this obviously superior gasket. I've never had any problems with anything I've purchased from FTFU, apart from a couple of decals which were replaced at no further cost. In fact it's been a real pleasure dealing with him. I was remiss in not excluding him from my condemnation of the other suppliers mentioned in my post above. Thanks for this info. His gaskets & Stag & we're sorted! Cheers
Peter TD 5801
P Hehir

Just a note to tell I reinstalled the sender after cleaning everything up. Using Hylomar there are no leaks with a full tank. I let it set for 3 days before filling the tank and all is well. PJ
Paul161

I reckoned you would get it!
Geoffrey M Baker

This thread was discussed between 12/08/2015 and 21/08/2015

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