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MG MGA - Fuel Tank Sender Unit

Please may I beg assistance with a continuing problem? As yesterday was 'Drive It Day', I took the MGA out for a trot. It hasn't done a lot of mileage over the last couple of years, but now that I've got the front brakes working really well it passed an MoT last week and I'm determined to get some use out of it this year. However, the fun faded a little as the drive continued because I'd put rather a lot of fuel in the tank, and thus triggered an old problem that I keep thinking I'd solved, and the stink of leaking petrol started to pervade the car.

The sender unit is, I think, the original, and I has it rebuilt a couple of years ago by a chap in Lancashire (if I remember correctly). I have had considerable trouble making the joint fuel proof, and I had forgotten that my usual strategy had been to keep the level in the tank fairly low. The original screws that hold it in had been stripped and have been replaced by 3/16" UNF screws. The gaskets have always been the cork type. I had been advised that these should be fitted dry but, on finding on previous occasions that this didn't seal, I have used Hylomar on the joint - a gasket seal which seems to be the only one to claim to be petrol proof. Well, it still leaks whenever there's plenty of petrol in the tank, so it looks as if I've got to take it off yet again. What I think I need to do, I suppose, is to find a hard-setting unleaded-proof gasket seal to really close the joint semi-permanently. Can anybody suggest anything suitable?

I shall start work on the removal in a couple of days time, now that I've drained the tank, but I am already entertaining suspicions that the unit itself is leaking through its cover, rather than the joint by which it fits to the tank. I presume there are tiny seals inside to allow the movement of the arm to 'wipe' the coil inside. Do these get damaged by unleaded? And, once it's dried out, how can I tell what's been happening?

Gus
Gus Gander

Gus, i had the same problem and resoved it simply by replacing the gakets with cork and using sealent. Be very generous with the sealent around the screw holes and yes you will have to replace the one on the cover as well. The cavity were the contact is does fill up with petroll as well. If your original one is working good, then put the time into fixing it as the new reproduction one's are junk!
Good luck!
WMR Bill

The coil bit is always soaked in fuel

The wiring connector should be fuel tight, and then there should be a rubber gasket between the body and the cover.

Why not tap out the threads in the tank and install new screws. I prefer to use a hex head screw because then you can tighten them better than is the case with just a slotted screw.

I have always used the cork gaskets, and have never had any problems.

Does anyone have a scrap unit with a good wiring connector at the bottom - then I can resurrect a good original sender.
dominic clancy

Thanks for the word. I didn't realise that the internals of the sender unit were supposed to fill with petrol. I'm a bit alarmed by the thought of a 12v current being conducted through the petrol by the 'wiping' arrangement, but I suppose it's OK if that's what was always intended. This increases my suspicion that it's the cover, or the terminal, that is dripping petrol, as I spent a great deal of time and attention in setting the joint right the last time I had this problem.

Any suggestions about a good gasket sealant to use? I've not managed to get a full understanding of what works (and is available) since unleaded petrol arrived. I've been messing about with old cars for more than 40 years now, and 'back then' all I needed was Hermetite Red for a soft non-setting coat, or Hermetite Green (which I would have used in this application) for a hard setting seal. I haven't seen these on sale for years, and suspect that neither would be proof against unleaded fuel now. Hylomar is my current favourite,as it claims to be petrol-proof, but I'm not too sure about it.

G
Gus Gander

I have used "Stag" on petrol unions/connections with excellent results!
Barry Bahnisch

Thanks for the tip, Barry, but I can't say I've seen 'Stag' over here. Meanwhile, here's a photo of the problem area. It looks, for the moment, as if the leak HAS been round the joint. There is still some wetness round the 10 o'clock region, and paint has been removed below the entire joint, so it'll all have to come off (again...)

G
Gus Gander

Sorry, I forgot to attach the photos, and now the 'Upload' button won't do anything.
Gus Gander

This thread was discussed between 21/04/2008 and 22/04/2008

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