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have I the wrong fuel cap??
AndyW - 28/4/13 at 08:42 PM

Evening,

I had the car running today to do a final test of the cooling system, all went well. Tonight I noticed the fuel tank had slightly changed shape. I looks like the top of the tank has been pushed in. My fuel cap is this one from CBS.

Now I could not see any difference between different types, the wife brought it for me for Christmas so she rang cbs and asked which one to order for my type of fuel system (I had written it down in case she rang and was asked any questions).

So it looks like my fuel tank is creating a vacuum as when I released the cap there was an intake of air and the tank popped back up. (this was only a few mm but noticeable)

Any idea's as to whether I need a tank vent and if so what type? I don't know much about it to be honest, I thought the vent was in the cap??

Help please

Thanks

Andy

jeffw - 28/4/13 at 08:46 PM

Yes you need a vent and no that cap doesn't have one.

big_wasa - 28/4/13 at 08:48 PM

Yep you need a vent.
It needs to let air in to replace the fuel, let air out to allow for expansion on a warm day yet not loose fuel if you tip the car upside down.

AndyW - 28/4/13 at 09:13 PM

OK shi*t,

so can I add a vent? Or new cap?

40inches - 29/4/13 at 07:31 AM

You can add a vent easily using an aircraft tank fitting

AndyW - 29/4/13 at 09:14 AM

quote:
Originally posted by 40inches
You can add a vent easily using an aircraft tank fitting


I don't understand how that would work, obviously it would vent the tank, but what about spillage? Would I then have to add a two way valve to allow air in and out and to prevent spills should the car and upside down?

I can exchange my fuel cap but mine fits a 62mm hole and the vented cap fits a 57mm hole. Need to get a easy quick fix asap as I'm about to apply for IVA

I see the add on valves are quite expensive, so I could just try and make the smaller new vented cap fit? what does any one think?? I'm now getting a tad pi$$ed off with things just as I seemed to be making progress again

scudderfish - 29/4/13 at 12:08 PM

quote:
Originally posted by 40inches
You can add a vent easily using an aircraft tank fitting


Don't drill a 0.5inch hole with that, used a stepped cutter. The drilled hole will not be circular and it will leak. I learnt that one the hard way.

40inches - 29/4/13 at 01:11 PM

quote:
Originally posted by AndyW
quote:
Originally posted by 40inches
You can add a vent easily using an aircraft tank fitting


I don't understand how that would work, obviously it would vent the tank, but what about spillage? Would I then have to add a two way valve to allow air in and out and to prevent spills should the car and upside down?

I can exchange my fuel cap but mine fits a 62mm hole and the vented cap fits a 57mm hole. Need to get a easy quick fix asap as I'm about to apply for IVA

I see the add on valves are quite expensive, so I could just try and make the smaller new vented cap fit? what does any one think?? I'm now getting a tad pi$$ed off with things just as I seemed to be making progress again


You don't have to have a rollover valve, it's just wise to fit one.Take the breather hose as high up, just inside the wheel arch, as possible, and make a down loop for about 75mm, like a shepherds crook.
And don't worry about IVA time scale. I applied on the 25th march, my appointment is on the 7th May

40inches - 29/4/13 at 01:12 PM

quote:
Originally posted by scudderfish
quote:
Originally posted by 40inches
You can add a vent easily using an aircraft tank fitting


Don't drill a 0.5inch hole with that, used a stepped cutter. The drilled hole will not be circular and it will leak. I learnt that one the hard way.


Good advice

AndyW - 29/4/13 at 02:27 PM

quote:
Originally posted by 40inches
quote:
Originally posted by scudderfish
quote:
Originally posted by 40inches
You can add a vent easily using an aircraft tank fitting


Don't drill a 0.5inch hole with that, used a stepped cutter. The drilled hole will not be circular and it will leak. I learnt that one the hard way.


Good advice



Thanks for the advice, will post an update later in week when bits arrive and fitted. One last question, my stepped cutter is metric so what is 0.5inch closest to in metric? What size did you guys use?

scudderfish - 29/4/13 at 03:26 PM

0.5inch is 12.7mm. Try a 12mm hole and put it in with violence/lubrication

I ended up buying a new tank and didn't bother with the fitting in the end. I had bought it so I could avoid taking my tank out, but as I ended up having to use a new one, I did it a different way.

Regards,
Dave

matt_gsxr - 29/4/13 at 04:51 PM

Why not fit a breather valve to your tank?

Like these ones
http://www.thinkauto.com/onewayvalves.htm

They you don't have to incur the stress and marital strife of returning the cap, and these work really well.

Matt

Irony - 29/4/13 at 05:36 PM

There's lots of info on here about the breather valves. The ones that let air in and out but not fuel in case of a roll over. You can create the same effect with a pipe routed the right way. I shall try and find a picture

Irony - 29/4/13 at 05:43 PM

See daviep's great idea on this thread. breather pipe thread