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MG Midget and Sprite Technical - Submerged Fuel Gauge Sender

Is there any concern about the fuel gauge sender getting buried in debris and crud? The sender sits in a well and there is a space between the fuel tank top and the bottom of the boot floor that will allow water to be splashed into the sender location.

When I removed the old tank the sender was buried in mud and dirt. The top of the fuel tank was so rusted that I had to replace it. The new tank is not only galvanized but coated in epoxy so I am not too concerned about that. But the sender sits in a depression and it looks like a fine place to collect water and debris.

I thought about adding a gasket surrounding three sides of the sender, leaving the back open to allow any moisture or fumes that may find their way in to eventually evaporate. What I found is that there is varying amounts of space between the tank and the boot floor. On the right side the gap is about 5/16", transitioning along the front side a section of the gap is 1/4" and another 9/16" and finally along the left side the gap is 3/16".

I cannot find a closed-cell foam gasket that is thick enough to seal the front yet soft enough to be compressed to 3/16". I thought about using an expandable foam sealant but I don't want to have things mucked up if I ever need to remove the tank for some reason. Maybe it is nothing to worry about but I envision the well filled with water and debris, submerging the signal and ground wires and the gauge not reading correctly. (The added ground wire is not original, but I think it will ensure a good electrical path.)

Has anyone tried to seal this area to keep it clean?

Thanks,
Paul


Paul Noeth

your car managed well enough for 45 years, do i wouldnt think its a problem
Mick struggling with the wiring

While your cellular foam seal might seem a good idea, I would worry about it trapping moisture against the boot (trunk) floor. As Mick says, it seems to work long term despite getting covered in muck.
Mike Howlett

Both above comments from Mick and Mike are very wise. I once did some restoration work on a Mk1 Ford Granada and the owner had used expanding foam between the inner and outer rear wings to prevent moisture ingress, but it had the opposite effect and the wings were completely shot.

Bernie.
b higginson

Thanks everyone. Not doing anything is definitely an option that I have been considering.

Mick said the car managed well enough for 45 years, but that is not the case. The car was last driven 1976 and it has been in dry storage since then. The reason it was taken off the road was that the hydraulic lines rusted through making it inoperable and the severe structural damage from corrosion made it unsafe to drive even if the lines were replaced. As was the case, it did not manage very well for even 10 years. The road salt and chemicals in this area can destroy a vehicle in a short time so I have been doing all I can to make the car last a little bit longer this time around.

It will be a frequent driver. It will see wet weather, dirt roads, and most likely be driven in the snow as well. It seems like a bad idea to have recesses that will hold water and debris and not drain.

Another approach I have been considering is to leave the gap open and seal the electrical connection only. I'll use dielectric grease on the connector itself to discourage corrosion, but also seal the connection with a coat of silicone adhesive over the connector sleeve. That way I won't have anything between the body and the tank while keeping moisture away from the connection, even if the sender is under water occasionally. It may not be a bad idea to get underneath now and then with a hose to flush out the area between the body and fuel tank.

Are there any negatives to sealing the electrical connection with silicone adhesive? All of the wiring is new.

Paul
Paul Noeth

for a frequent driver, the goal will be to cover all internal body / structural surfaces (and the top of the fuel tank) with a good, Waxoyl (or equivalent) sealer/protectant, and to re-apply periodically over time to maintain the good seal. Make sure to keep all of the body drain holes open (do NOT seal up any of the areas that need to drain and breathe). I like to coat the springs and other under-body suspension parts with Waxoyl as well, to keep surface rust at bay, in the winter.

electrical connections ideally should all be coated with a di-electric grease before assembly, as it will exclude water in the joint, much like waxoyl does for body panels. Any auto parts store should sell tubes of this stuff.

for hydraulic lines, using a non-ferrous material (my favorite is copper-nickel tubing like used in the marine industry) will go a long way to preventing a re-occurrence of your corrosion issues there. Note, however, that all of the end fittings will still be zinc plated steel and will corrode so it is a good idea to coat their threaded surfaces with a bit of anti-seize grease before assembly (don't get any on the sealing surfaces, just the threads for easy removal when it is time to renew brake cylinders and hoses as the years pass).

for all fasteners, it is also a good idea to use anti-seize on everything, to help exclude moisture, and oxygen, from causing corrosion in the joints. Be sure, though, to reduce all of your torques by the necessary 25% ~ 45% to compensate for the reduced friction during assembly that the anti-seize creates (therefore less torque is required for the same stretch - check the manufacturer's information to be sure of the %). I made a list of torques for the various sized fasteners and reduced them all by the 42% that my anti-seized I used called for, and posted it beside my torque wrench so that during my rebuild I could easily keep using the correct, lower values.

Modern epoxy based body paints have an amazing capability for sealing and protecting steel panels, one popular line in the US is POR-15, which makes a whole range of paints for various purposes. The idea is to seal everything up so well, and then cover it with greasy wax (waxoyl) and drive during all the salt and rain and just laugh it off!


Norm
Norm Kerr

<<The idea is to seal everything up so well, and then cover it with greasy wax (waxoyl) and drive during all the salt and rain and just laugh it off!>>

Norm, exactly right!!

I've done most of what you suggest. I have used copper-nickle tubing to replace all of the hydraulic and fuel lines, but I did not put anti-seize on the fitting threads. Since I have not installed the brake fluid as yet I should go back and do that.

Off topic, but I am a little concerned about using anti-seize on everything. Before I got into this rust bucket I used lock-tight to keep fasteners from coming loose. Now I am using anti-seize with concerns that I will be shedding parts as I go down the road. I am hoping that frequent inspections after it is running again will ease my mind. On the front shocks I did drill and safety wire the bolts to prevent them from coming loose since they are such an integral part of the suspension. Also I have been careful not to get the anti-seize under the washer or bolt head, only on the threads and sparingly at that.

Thanks,
Paul



Paul Noeth

Anti-seize should not mean that fasteners will come undone. In fact threads are intended to be lubricated before tightening them to the correct torque.
Mike Howlett

Mike is exactly correct, the presence of the anti-seize will not make the fasteners come loose just because they are slippery. The clamping load is provided by the stretch of the fastener, and when it is correct all the oil in the world won't interfere with that.


But regarding the correct torque,

"correct torque" is a term that relies very much on the friction in the joint while torquing, and while Mike is correct that the most accurate way to torque fasteners is lubed, the right torque value will be a different, lower value than the "dry" number cited in the shop manual

For example, the most common fastener on a midget, the 5/16-24, grade 5, is listed in the book to be torqued to 19 ftlbs dry. When using anti-seize it must be reduced to 11 ftlbs, according to Loc-tite, the source of mine, or -42%. Ideally, you should check what the % is for the stuff you buy, just in case.

The second most common fastener is the 3/8-24, grade 5, the manual says 34 (or 35, I forget), but if using anti-seize, that is reduced to 20 ftlbs.

The reason why this is so important is because the correct stretch in the fastener is what holds the joint together, and it is just as bad to go OVER the correct amount as it is to go under it. Torquing to more than is called for causes the fastener to yield, and not necessarily all at once, it can gradually yield and work itself loose 10,000 miles later.

Carefully keeping within the proper torque prevents this.

By the way, the torque values given are usually around 75% of the elastic limit of the steel, which is a nice "safety factor" which allows some slop in our handling of them.

When doing a rebuild it is a nice idea to replace all of the structural fasteners because one never knows what shenanigans your DPO was up to with them.

Norm
Norm Kerr

That's a really helpful post Norm, thanks. I have a little table that shows exactly what you are saying for all common UNF bolt sizes. It's surprising how low some of the torque values are.
Mike Howlett

Perhaps we should have started a new thread titled, "corrosion protection", and another one called, "UNF torque", because this has drifted away from "how to protect the fuel sender", but somehow that won't stop me from posting just one more thing, I finally (FINALLY!) figured out how to save my .pdf files as .jpg files so that I can upload them here. It is super easy and I feel like a dunce for having taken so long to realize it.

This attachment is a list of torques calculated for when using anti-seize, with some notes about fasteners in general. I made this for myself when re-assembling my car to be a quick reference / keep my head straight. The information itself is available from myriad other sources, but bringing it together into one simple "worksheet" made it most useful to me.

Maybe it will be equally useful to others.


Norm


Norm Kerr

The torque chart is very helpful, I've got a copy in the garage. Thanks Norm.
Paul Noeth

I do the same as Norm & Mike, anti sieze on everything; threads,under heads/washers etc and reduce the torque by 40%. This leaves the torque values low as previously mentioned but don't worry in the long run it works a treat, the next time you want to undo something. For your own peace of mind you might want to replace all the spring washers as you go, but things certainly wont be falling off going down the road.
Ian
Ian Webb '73 GAN5

Thanks for that page Norm. I shall keep it in my garage.
Mike Howlett

This thread was discussed between 21/04/2011 and 28/04/2011

MG Midget and Sprite Technical index

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