Print

[oilstain]

O/T not a series part but a part in my 11a

Does anyone know the part number for the seal in the fuel cap - stc4072, as pictured 

my seal can leak when the fuel spashes around!

[diffwhine]

I've just had a look on the JLR EPC and as far as I can tell. it isn't available as a separate part. The cap itself isn't horrendously expensive (about £10 from Paddock).

[oilstain]

I have bought a new cap, not the one pictured, but fuel still gets out when its sloshes about and thought a double seal might do the job
hence why I wanted a second one
(its on a top fill, lightweight type, underseat tank, so the fuel is close to the cap)

[diffwhine]

I think you might have hit a problem there... Those caps are designed to vent, so it may not be the seal at all - it may be the cap itself causing problems. Remember that on a Defender, that would sit much higher than the tank.

I have experience of this... I had a 110 fitted with a Mazda SL35T diesel engine. I do miss that vehicle! When the Bunsfield Oil depot blew up some years ago, there were major issues with fuel quality at our local station (they ran the tanks too low). A lot of jelly type debris was drawn into fuel tanks in the local area. In my case it blocked the vents in the filler cap. On the way back from Devon one evening, the LR died. When I looked underneath, the steel fuel tank has collapsed like a crisp bag because of the vacuum caused by the blocked cap. When I released the cap, there was a noticeable rush of air into the tank. Cost me (actually Total) a new tank and a full fuel system flush + recovery costs.

[oilstain]

When I bought the tank new the cap came with it, it was listed as a Bearmash tank but I'm unsure if this was marked on the box

When looking for the leak, I removed the cap and the lip of the tank where the cap seal sits looks wet which made me think the seal was not thick enough.....

[diffwhine]

Fair enough! Maybe you could fettle the tangs on the cap to make it pull up a bit tighter? I've tried the double seal trick a few times on various projects and it never seemed to work for me.

[oilstain]

Today I took apart both caps, once you remove the 2 screws that hold the metal plate and seal you can take it apart.
Under the metal "lock" plate you can lift out the rubber seal which is bonded to a another metal plate the size of the seal, under that are on one cap 2 metal thin wavey washers that spring up the seal plate but on the other only 1 thin wavey washer, however it was the cap with 2 washers that was leaking
I rebuilt the newer cap with all 3 thin wavey washers that seem to tighten the seal to the tank a little and I will see how that works before I try to bend anything or perhaps add a plain washer as I have no move wavey type.
Also the bonded on metal plate has ribs that must engage with the metal wavey washer/s.

Only time will tell....

[GlenAnderson]

How does the tank vent? If you seal it up too well without any way for air to get in then you'll not drive far before you run into problems.

[oilstain]

How does the tank vent? If you seal it up too well without any way for air to get in then you'll not drive far before you run into problems.

I'm not sure
If the presure built up in the tank due to hot weather the wavey washer would compress and let air out ? but I'm at a loss how air gets in but the seal does not go tight to the cap sides and the internal parts seem to have a number of holes but I'm unsure if it vents

[diffwhine]

Looking at EPC, there are 4 Defender filler caps listed.

RTC4740 which is a locking vented cap. This supersedes to STC4072 locking vented cap
RTC4741 is a grey non vented locking cap

NTC2757 is listed as a non vented cap without a lock for petrol vehicles (bizarrely identified as "For Unleaded Fuel")

Not sure where that leaves us other than the point being that the only cap without a lock appears to be this petrol one NTC2757. Therefore is it possible that you have an NTC2757 and not what you think you have (RTC4740 / STC4072)?

On a standard Defender, for this era, the fuel fillers are the same part number between petrol and diesel, so any cap should physically fit. I can't see why you would build a vehicle with a non-vented cap in that era unless there was some unique territory emissions requirement and some sort of EVAPS system fitted

[oilstain]

When I bought the tank, new, a air portable underseat type, it had a non locking cap but I think the tank was listed as a petrol tank, and I used it for petrol for a period in a 86" and the cap does not have a key slot.
I now use the tank for diesel in a 88".
If I now use a cap with a lock it will be a vented type and OK for diesel?
I don't understand why petrol does not need a breather but diesel does

[GlenAnderson]

Probably because modern petrol tanks aren’t allowed to be vented to atmosphere like they used to be. They’re normally vented either through a form of filter, or to the engine’s emissions control system.

[oilstain]

So if I use a cap with a lock hole but perhaps remove the internal locking bar I will have a venterlated non locking cap
I'm unsure of the need for a locking cap on a tank under the drivers seat that requires the door to be unlocked to get to it
With regard to what you said I would have thought most underseat fill tanks are sold to people with older engine systems with no form of vents or filters
I wonder if I just drill a pin hole in the top of the non lockable cap it would do the job as the only "vent" in the lockable cap must be through the key slot although it does have a shotter (perhaps not a air tight shutter )