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So, both of the petrol caps on my car leak when the tanks are full. I find this annoying and my paint doesn’t like it either. Looking closely at the filler neck on the car it looks like there are two high spots on the track that engages the petrol cap - 1 at the beginning of the track (when you first engage the cap) and the second is just before the end of the track. The net impact is that if I swap in too thick of a seal then it is really hard to get the cap started and then at the end the pressure on the cap is slightly less - I guess in both cases this is to prevent the cap from undoing itself.

Questions: is this normal for everyone? Do you have solutions other than switching to a non-standard cap (I want to stick with the standard caps)?

You need to get a couple of ethanol compliant fuel filler cap seals. I put up with exactly the same for a year or so until ite dawned on me. Catmint do them.

Peter Laidler wrote: ↑Tue Nov 15, 2022 9:38 pm Catmint do them

Sorry Peter, it's not me

i have the same problem ...
So if anybody can help, I listen

Try Fred at Nippy Cars for fuel cap seals

apblake wrote: ↑Tue Nov 15, 2022 8:47 pm So, both of the petrol caps on my car leak when the tanks are full. I find this annoying and my paint doesn’t like it either. Looking closely at the filler neck on the car it looks like there are two high spots on the track that engages the petrol cap - 1 at the beginning of the track (when you first engage the cap) and the second is just before the end of the track. The net impact is that if I swap in too thick of a seal then it is really hard to get the cap started and then at the end the pressure on the cap is slightly less - I guess in both cases this is to prevent the cap from undoing itself.

Questions: is this normal for everyone? Do you have solutions other than switching to a non-standard cap (I want to stick with the standard caps)?

60's/70's that was common on a car with twin tanks, when parked on a heavy cambered road when your tanks were full.

Apologies for blaming you Gordon.....! It's called 'passing-the-buck' I got a set of 3 tank seals, 2x filler cap and 1x sender unit seal for the all-in price of a tenner at Beaulieu. Only recently fitted the sender unit one, so the ethanol seals are available.

Forumers have GOT to take note and be aware that the new fuel is slowly destroying the old rubber fuel pipe seals. You don't see it....., the hoses look fine but the distinct fuel smell is ever present until you're driving back home and the hose collapses............

Ok I’ll try Fred at Nippycars. I’ve replaced all 8 flexible fuel hoses on my car and I’m replacing the gasket for the fuel sender this weekend. I guess that just leaves the fuel cap seals at this point. We have E10 fuel as the dominant blend in the US and I think it is probably easier to harden the car against it than it is to try to avoid the fuel. They tried to get 15% ethanol fuel into pumps this summer but fortunately I didn’t see any around me.

I would also check that your petrol caps do not have breather holes in them, as these will let fuel out aswell as air in. Some caps just have holes in them!
I know the later tanks have breathers inbuilt so they dont need a vented cap. Not sure about the early tanks

In my opinion every mini Tank is vented and has the small plastic hose that goes from the top of the Fuel tank down to the outside in the boot floor...

Not sure about the later 34 Liter Tank but the Injection Cars had another system.

I’ll have to double check but I’m pretty sure my caps have vent holes in them. Do they not all have vents? At least all the standard ones?

I agree that a vent seems unnecessary in the cap given the vent in the tank, but maybe someone else has a reason why it should exist. But again I thought it was a moot point because I thought all the caps were vented??

The tanks are vented not the caps.

Whe used to solder the holes in the Aston Style Petrol Caps exactly because there was always some petrol going out of these vent holes

My '88 Mini had this issue as well. The filler neck had what looked like worn "notches" where the ears of the cap engage at fully turned closed position. Fuel would always spill out from under the seal when more than 3/4 full. Tried new seals, no improvement. New fuel cap, same screw on type, same problem. One solution was to chop the filler neck off, weld on new one. Someone also suggested taking one of the "fake" filler necks people stick on opposite side to pretend to be a true Cooper S twin tank setup, and weld/epoxy it over the original neck (trimming the worn flange of first).

But I solved it completely by fitting a Monza style flip cap...the type that had a brass collar with interference fit over the original neck. Collar is outside threaded and has a flange for the flip cap to seal against. Does not use the original sealing surface for keeping the fuel in. I used gaskets between the collar and original neck flange and between flip cap and collar, plus pie sealing goo (a locktite product 515 Gasket maker which is fuel resistant). Flip cap did have a vent hole, but my tank has a vent line so I filled the cap vent with epoxy on the underside. Not leaks since.