Morris Minor Owners Club

I’d been having issues with the boot and cabin of my saloon smelling strongly of petrol fumes for a while.

To remedy the problem I replaced the petrol tank with a brand new heritage one. I also replaced both sender unit gaskets with viton ones, smearing a small amount of copper grease on them to help with the seal. The old top sender unit gasket looked past it’s best but the old bottom one looked okay. I was careful not to over-tighten them.

I also replaced the fuel filler hose, which was original but looked okay, while I was at it. I used a slight smear of grease to help the new one on and it’s on nice and tight with jubilee clips.

Some flaking paint within the boot was rubbed down, metal cleaned, primed and re-painted. Same was done around the tank lip.

I’m frustrated to find the car is still suffering from the petrol fume problem. If I leave the boot open for a while and have a sniff around I can’t detect where it’s coming from. There are no visible fuel leaks anywhere when filling up or when the car is running.

So I think it must either still be the gaskets or filler hose to blame?

Has anyone else had the same issue, and are any material of gasket/filler hose better at stopping fuel odour than another?

(To add to the frustration the old tank upon inspection looked much better than expected and appears totally sound. So it probably wasn’t the previous tank causing the smell in the first place.)

An expensive non-repair! How many times do I have to ‘bang on’ about diagnosis rather than blind replacement!

First thing to check is tank ventilation.

I have to say replacing the tank was an extreme first move
I had a petrol smell in the boot back in 2017 when I brought the car. Note the comment from myoldjalopy.

See here: viewtopic.php?f=12&t=67392&hilit=fuel+tank

It certainly was expensive, though fortunately I know someone nearby who may be able to use the old tank in one of his two projects...so all is not lost.

It was after filling the new one 3/4 up that the odour returned. (Previously I was driving around with my window open all the time to avoid buzzing on fumes. It doesn’t seem quite as bad now).

I have spare cork gaskets, I suppose I could give them a try instead of the viton ones to see if that resolves it?

I also wondered whether I could put a rubber seal around the back of the rear seat, so it forms a seal with the boot area and stops odours getting into the cabin?

Comment noted berni. The new flexible hose has been on the car now for over a week.

I can't see trying to seal the back seat will work........!
But one thing to consider - you say it occurs when over 3/4 full. I had a fuel smell when driving up steep hills and I don't know if your petrol smell is worse after hills or sharp cornering but it was simply the seal on the fuel cap itself. See here: viewtopic.php?f=6&t=70328

Have you checked the large rubber hose that connects the petrol cap to the tank. I had one from one if the major suppliers that sweated fuel. Not enough to see but when you took it off you could smell it

“To remedy the problem I replaced the petrol tank with a brand new heritage one. I also replaced both sender unit gaskets with viton ones, smearing a small amount of copper grease on them to help with the seal. The old top sender unit gasket looked past it’s best but the old bottom one looked okay. I was careful not to over-tighten them”

I would clean off the copper grease and fit them clean and dry.

Thanks for the replies.

The flexible hose connecting the filler pipe to the tank is brand new from ESM and fitted tightly at both ends. Unlikely to be defective.

The car is sitting level in a garage and has been for a week. I only took it a short run for petrol. There were steep hills on the way back but no visible sign of petrol seeping out of the sender unit, or anywhere else.

I didn’t think a little smear of grease on new gaskets would do any harm, or cause fuel odour to escape. Fairly common practice? I think one of them is the most likely culprit though.

I do have new cork fuel sender gaskets. I could try replacing the viton (Moss Europe) ones with the cork type (either with or without hylomar blue).

Steep hills on the way back? OK, so check the filler cap - is the circular seal in good condition? As I said, my fumes problem was solved by fitting a new seal inside the cap. The old one was very thin and breaking up.

Thanks, I’ll check that and if it’s old replace it. It’s the only one I’ve not changed.

Would that cause fumes inside the boot area, when the filler cap is outside?

myoldjalopy wrote: ↑Tue Mar 09, 2021 7:57 am Steep hills on the way back? OK, so check the filler cap - is the circular seal in good condition? As I said, my fumes problem was solved by fitting a new seal inside the cap. The old one was very thin and breaking up.

Yes, it did in my case. I suppose the petrol leaked out and then dribbled its way into the boot via the filler neck, especially if the rubber seal between the car body and the filler neck is perished. Come to think of it, I replaced that at the same time as the cap seal as it had gone quite goo-ey, so another thing to check......

Ah yes, I’m with you now. Thanks. Good luck with the rubber.

MorrisJohn wrote: ↑Tue Mar 09, 2021 8:31 am Thanks, I’ll check that and if it’s old replace it. It’s the only one I’ve not changed.

Would that cause fumes inside the boot area, when the filler cap is outside?

The scenario is that the filler cap with a bad seal allows fuel to leak out and then run down the outside of the filler into the boot past the bodywork seal. Only a tiny amount will give you a fumes smell in the boot.

The vent in the cap tends to be a mere pin hole and also behind a baffle, as it only has to allow a miniscule airflow as the fuel is used up.
A perished or broken seal could literally allow a half a teaspoon worth at every 'slop' of the tank.

What I said....

myoldjalopy wrote: ↑Tue Mar 09, 2021 9:25 am What I said....

Yes, we were typing at the same time
I also explained the difference between a working 'vent' and the perished seal/gasket, which has been a subject of discussion in the past.

Thank you gents, much appreciated.

How is the old gasket removed from the filler cap and replaced? It’s held in place with jointing compound I assume? It looks a bit awkward to get at.

I will go ahead and replace it and it will either rule that out as a possible cause or fix it.

Depends on the cap.
I've got a Locking Cap on mine which is a rubber material.
If you have the original non-locking cap, then I believe it's a cork gasket held in with an adhesive.

I think 2 part epoxy adhesive, ie Araldite, is fuel resistant when cured.

Thanks. It’s non locking original type held on with a chain. It’s got a viton gasket fitted.

Did the OP check the cap breather hole for a blockage? Can’t remember reading that he did. If that is blocked, the tank will not be ventilated and quite soon be under pressure with modern fuels. Any pressure is likely to allow fumes or fuel to pass any small gap that would not normally pass either.

MorrisJohn wrote: ↑Tue Mar 09, 2021 4:17 pm Thanks. It’s non locking original type held on with a chain. It’s got a viton gasket fitted.

Perhaps that's the problem then; I've only ever seen cork ones sold for those caps. Perhaps someone else with greater experience of the standard cap can give an answer.