Morris Minor Owners Club

I bought and fitted a second hand petrol tank 4 years ago.
It looked nice and clean inside and out. The outside had been painted with stonechip.
A few days ago I kept getting a whiff of petrol from near the car.
Today I had a look under and saw that the tank is leaking from one spot on the bottom close to the drain hole.
Rubbing the paint off with my fingers has revealed about 2 square inches of filler. I have not investigated further yet, but it seems to be a small hole, most likely damage from something rather than rust. The tank is not wafer thin; it seems very sound. The car stands for long periods, but I only put E5 petrol in it.

How do I go about mending the hole? The filler, whatever it is, has held the leak back for 4 years....so quite impressive!

Thanks.
John

I have braised many fuel tanks but you have to be very careful.
Once tank has been thoroughly washed out it then needs degassing , you can connect a car exhaust pipe to the filler neck and let it pump through the tank. I then fill the tank with water and turn it until small air pocket at the repair point.
I cannot stress enough how dangerous the vapour is even if you think the tank is empty . If you are inexperienced then let someone else repair it or buy a new tank. Do not risk your safety!
Their are also cold repair liquid metal types of sealant.

There's quite a few specialist, fuel resistant, compounds on the market.
Plastic Padding, Isopon, J-B Weld, Permatex, POR-15 and Quiksteel are amongst the more popular brands.
They come in 2 categories, either an epoxy putty to fill a 'hole' or a liquid to swill around and seal up more porous micro holes.

If you confirm it is a single hole from a sharp object, the putty type is probably your best bet.

Thanks both. Could I Mig weld it if it is just a puncture ?

Are the putty repairs considered permanent?

stuffedpike20 wrote: ↑Tue Dec 09, 2025 5:33 pm Thanks both. Could I Mig weld it if it is just a puncture ?

Are the putty repairs considered permanent?

If I was going to mig, I would weld a patch so it's to the thicker material away from the corrosion. Your welding skills will need to be able to weld with no porosity not important when patching body or chassis but fuel will find the tiniest pin hole.
All the safety warnings still apply.

Depends which product you use and how careful the preparation, the previous one, you say lasted 4 years. Did the product fail or has the corrosion spread?

A old fashioned repairer will solder a patch over the corroded area. It might be worth asking for a quote. Then you do not have to worry about safety as somebody else will be doing the work.


Stephen

Bill_qaz wrote: ↑Tue Dec 09, 2025 6:27 pm

stuffedpike20 wrote: ↑Tue Dec 09, 2025 5:33 pm Thanks both. Could I Mig weld it if it is just a puncture ?

Are the putty repairs considered permanent?

If I was going to mig, I would weld a patch so it's to the thicker material away from the corrosion. Your welding skills will need to be able to weld with no porosity not important when patching body or chassis but fuel will find the tiniest pin hole.
All the safety warnings still apply.

Depends which product you use and how careful the preparation, the previous one, you say lasted 4 years. Did the product fail or has the corrosion spread?

Thanks.
I need to get the tank off and investigate furhther. I hope it is not corrosion, but a puncture through sound metal.

svenedin wrote: ↑Tue Dec 09, 2025 6:39 pm A old fashioned repairer will solder a patch over the corroded area. It might be worth asking for a quote. Then you do not have to worry about safety as somebody else will be doing the work.


Stephen

I have no idea who I could ask.
Looking online, there was a suggestion that a minimum cost could be £200.....which is a big chunk of the price of a new tank.
I am sure it could be brazed or soldered, but don't know who to ask. There used to be a Serk Marston close to me, but not now.

I soldered mine you need a Large soldering iron and perfectly clean metal,heat the iron well away from tank,Black heat from the iron is not a problem

I have seen radiators soldered before.
It's a shame that the little workshops that used to do these things are rare these days.

stuffedpike20 wrote: ↑Tue Dec 09, 2025 8:41 pm

Bill_qaz wrote: ↑Tue Dec 09, 2025 6:27 pm

stuffedpike20 wrote: ↑Tue Dec 09, 2025 5:33 pm Thanks both. Could I Mig weld it if it is just a puncture ?

Are the putty repairs considered permanent?

If I was going to mig, I would weld a patch so it's to the thicker material away from the corrosion. Your welding skills will need to be able to weld with no porosity not important when patching body or chassis but fuel will find the tiniest pin hole.
All the safety warnings still apply.

Depends which product you use and how careful the preparation, the previous one, you say lasted 4 years. Did the product fail or has the corrosion spread?

Thanks.
I need to get the tank off and investigate furhther. I hope it is not corrosion, but a puncture through sound metal.

If it not excessive corrosion then thoroughly clean and use one of the jb weld type products. If it a puncture hole is on a flat area and depending on access via filler and sender unit hole you could drill it and put a nut and bolt with fibre washers. Maybe jb weld type stuff over it as belt and braces.
When repaired put a bit of petrol in and tilt so its at the repair area and leave for a while to check before refitting.
Nothing to loose giving it a try as replacement tank or professional repair is going to be expensive.
Good luck

Bill_qaz wrote: ↑Wed Dec 10, 2025 11:28 am

stuffedpike20 wrote: ↑Tue Dec 09, 2025 8:41 pm

Bill_qaz wrote: ↑Tue Dec 09, 2025 6:27 pm

If I was going to mig, I would weld a patch so it's to the thicker material away from the corrosion. Your welding skills will need to be able to weld with no porosity not important when patching body or chassis but fuel will find the tiniest pin hole.
All the safety warnings still apply.

Depends which product you use and how careful the preparation, the previous one, you say lasted 4 years. Did the product fail or has the corrosion spread?

Thanks.
I need to get the tank off and investigate furhther. I hope it is not corrosion, but a puncture through sound metal.

If it not excessive corrosion then thoroughly clean and use one of the jb weld type products. If it a puncture hole is on a flat area and depending on access via filler and sender unit hole you could drill it and put a nut and bolt with fibre washers. Maybe jb weld type stuff over it as belt and braces.
When repaired put a bit of petrol in and tilt so its at the repair area and leave for a while to check before refitting.
Nothing to loose giving it a try as replacement tank or professional repair is going to be expensive.
Good luck

Thanks Bill.
I have got an update....and some questions.
I took the tank off and cleaned the filler away.
There are two puncture holes about 14mm apart and about 50mm from the drain plug.. It looks like someone litterally punched two holes through using a hammer and small nail.The tank metal is very sound.
The holes are about 2.5mm diameter, and the punching has caused a dimple in the metal.
I have got a mechanic on my street who says he can silver solder the holes. He proposes making 2 little steel top hats to put into the holes to prevent the solder running through. He wants me to clean the tank inside with soda crystals and boiling water first.
Questions.....Is silver solder going to be strong enough? (I would put putty over too).
When I have cleaned the inside of the tank, can I slosh a bit of oil into it to prevent rust for the time being?
I am going to use a polystrip disc to clean the rest of the bottom of the tank to see if there is any more filler, or holes.
If I paint Fertan over the bare metal, can I then spray with etch primer and then stonechip? I saw someone putting etch over Fertan on youtube, and it seemed a strange combination.
Thanks, in anticipation,
John

Silver solder will be fine. Its possible that epoxy araldite will work but im not sure if its compatible with ethanol. The same caution applies to soft soldering.

Yes silver solder will be fine it lower temp than brazed. Don't know about Fertan? I use old fashion red oxide undercoat and spray over with underseal but every one has a favourite formula.
After internal cleaning sloshing a gallon of diesel around will prevent rusting and will not harm fuel system with any residue after it been emptied.
I know I'm repeating but please be carful with petrol vapour when repairing. With lifetime in the industry I've seen and heard some nasty incidents. No such thing as over cautious

Thanks Bill, and woodypup, and everyone!

A little update.
I got impatient today and got the Mig welder out.
Drilled some little holes in some thin steel....set the welder up...and filled them beautifully.
Moved over to the petrol tank. The result.....one of the little holes is now bigger!

I would not advise anyone to try Mig welding a moggy petrol tank. They look like reasonably thick weldable metal...but are not!

I was concerned by comments that ethanol might eat through soft, or silver solder. But I guess it would take a long time.
Going to let my mate soft solder it, and then apply putty.

Is this post for real.
Just buy a new one.
Around £200.

It's a fuel tank.

It's not like we have a 1950 Triumph motorcycle (or any other vintage motorcycle) leaking fuel tank.

brixtonmorris wrote: ↑Mon Dec 29, 2025 11:58 pm Is this post for real.
Just buy a new one.
Around £200.

It's a fuel tank.

It's not like we have a 1950 Triumph motorcycle (or any other vintage motorcycle) leaking fuel tank.

Yes it is for real. The reproduction tanks are not as good as the originals. There are two types of saloon tanks available. One type has a drain plug but I am told by the Morris Minor workshop that they are a poor fit which often requires cutting parts of the car. That to my mind is totally unacceptable. The other type (different manufacturer) is a good fit but lacks a drain. It used to be common practice to repair fuel tanks by soldering a patch over the hole and there were specialists who did this for a living.

Stephen

stuffedpike20 wrote: ↑Thu Dec 11, 2025 3:37 pm A little update.
I got impatient today and got the Mig welder out.
Drilled some little holes in some thin steel....set the welder up...and filled them beautifully.
Moved over to the petrol tank. The result.....one of the little holes is now bigger!

I would not advise anyone to try Mig welding a moggy petrol tank. They look like reasonably thick weldable metal...but are not!

I was concerned by comments that ethanol might eat through soft, or silver solder. But I guess it would take a long time.
Going to let my mate soft solder it, and then apply putty.

Have you tried getting a quote from a professional repairer such as below, (just an example) maybe one local to you if you searched.

https://share.google/hlw8gYRO49TzC6MWD

It's all just nonsense.

As much is I like originality, its a fuel tank.

If the tank has rust holes it means that the whole tank is rusty.
The metal thickness is reduced across the tank on the lower part.
I have also seen rust holes on the on the seam where the top half and lower meet.

A quote from stuffed pike. "Drilled some little holes in some thin steel....set the welder up...and filled them beautifully.
Moved over to the petrol tank. The result.....one of the little holes is now bigger!"

Why? because the metal is so thin due to rust.

Also this nonsense about new manufactured tanks are not as good as the original Stephen.
That may be the case. They don't make e type jags anymore.

Enjoy your rusty fuel tank.

The drain hole serves no purpose, you have an electric fuel pump to pump the fuel out.
No need to drain it out fully the drain hole as a new tank will not have any rust in it.
Unless you fill it with diesel
All the drain hole does is allow people to steal your fuel.

When you get a new hole in the skin of the tank you will lose your fuel again.
Hope it does not happen far from home.