tank breather

Patrick · #1 1st April 2008, 22:59

I've notice my tank gets massively pressurised, seem the kit breather may not be ideal for injected engines. Also when there's a slosh of fuel it lets out a waft of petrol into the boot area which really is not very pleasant.

So I think I'm going to have to go for full blown proper two way one like this:

http://www.merlinmotorsport.co.uk/FU...duct_info.html

Bit expensive though. However its a safety item. Anyone know any cheaper ones that do the same job?

alackofspeed · #2 1st April 2008, 23:10

Same issue with the 5exi - I realised the issue very early on, and fitted a Mocal valve.

Not the type you've sent a link to, but a smaller item that you put in the top of the tank.

It's a good quality item.

MartinClan · #3 2nd April 2008, 07:41

I also noticed this problem. I am sure someone said you can cure the pressurising by drilling a very tiny breather hole in the filler cap (Post SVA) - but the mocal valve looks like a better solution. I guess it will need venting to the outside though.

Robin

Patrick · #4 2nd April 2008, 09:33

I've decided to get the mocal one. Last thing I need is a ruptured tank due to too much pressure! Although it will take a hell of a lot when I had a friend weld up the holes in it we put enough pressure in to bulge the ali (oops!)

MartinClan · #5 2nd April 2008, 12:12

Quote:

Originally Posted by alackofspeed

Same issue with the 5exi - I realised the issue very early on, and fitted a Mocal valve.

Not the type you've sent a link to, but a smaller item that you put in the top of the tank.

It's a good quality item.

Hello alackofspeed

I assume you meant this one:

http://www.merlinmotorsport.co.uk/p3...duct_info.html

Please could you tell me where you got the matching nut from? I am not familiar with this strange 6JIC thread...

Thanks

Robin

Patrick · #6 2nd April 2008, 13:04

I couldn't find a tap for the thread which is why I went for the inline one.

GreatOldOne · #7 2nd April 2008, 16:37

Quote:

Originally Posted by MartinClan

Please could you tell me where you got the matching nut from? I am not familiar with this strange 6JIC thread...

Thanks

Robin

Robin - I think it comes with a nut supplied. Or at least it does if you buy direct from Mocal:

http://www.thinkauto.com/onewayvalves.htm
http://www.thinkauto.com/acatalog/On...alves_268.html

RobDorey · #8 2nd April 2008, 18:30

I noticed the tank pressurising earlier and I've solved this by taking the marlin valve apart and making a tiny slot in the rubber sealing disc, so that the valve 'leaks' back very slightly. I've mounted the valve just above the tank and connected it to a steel breather pipe which runs up to the highest point in the rear tub (above the shock mount) and then returns to the rear centre and vents behind the tank, level with the edge of the tub.
So you'll have a valve which breathes in when the tank is being emptied, and slowly breathes out when the engine is stopped and the pressure could build in the tank.

alackofspeed · #9 2nd April 2008, 21:24

The mocal valve has a part specific nut, which is designed to work with the breather - you can't use a normal nut / tap a thread into a tank, and screw the valve in, as one of the vent holes is right by the flange of the valve.

The valve should come with the correct nut, though it took demon tweeks 3 attempts to get mine to me!

It works a treat, with only very minor petrol leakage, very occasionally - the leak is so negligile, that there's never a smell of petrol.

peterux · #10 2nd April 2008, 22:12

Quote:

Originally Posted by RobDorey

I noticed the tank pressurising earlier and I've solved this by taking the marlin valve apart and making a tiny slot in the rubber sealing disc, so that the valve 'leaks' back very slightly. I've mounted the valve just above the tank and connected it to a steel breather pipe which runs up to the highest point in the rear tub (above the shock mount) and then returns to the rear centre and vents behind the tank, level with the edge of the tub.
So you'll have a valve which breathes in when the tank is being emptied, and slowly breathes out when the engine is stopped and the pressure could build in the tank.

Thanks, Rob.
I have the Marlin supplied one way valve which I have vented with a piece of pipe through a hole at the top of the shock column.
If I can reach it with the rear tub on, i'll try your modification.
Presumably it's just a single slit with a stanley knife?

Peter

Patrick · #11 3rd April 2008, 20:46

Fitted the mocal valve today brimmed the tank and went for a long drive - no more petrol small wafting through the car when accelerating hard or going up a hill!

MartinClan · #12 4th April 2008, 09:05

Quote:

Originally Posted by alackofspeed

Same issue with the 5exi - I realised the issue very early on, and fitted a Mocal valve.

Not the type you've sent a link to, but a smaller item that you put in the top of the tank.

It's a good quality item.

Hello ALackOfSpeed

Can you tell me which valve you used and did you have to weld the nut to the tank or can you just bolt the breather through with the nut on the inside. It's a bit unclear from the Mocal web site and I don't want to get the wrong one!

Thanks, Robin

MartinClan · #13 7th April 2008, 11:34

The more I think about the breather valve the more I wonder if it is a lot of fuss about nothing. If you really had a disaster and flipped the car it wouldn't take much force to stove in the rear moulding. The filler pipe would probably pop off the tank and out would pour the petrol. The breather valve wouldn't make much difference then!

I reckon a small bore pipe from the tank going up to the top of the rear moulding and then down at the back somewhere so that it exits BELOW the lowest level of the tank would do the job just as well. If the car is ever upside down (Arghhh) then the breather would be ABOVE the tank.

What does the forum think?

Robin

Patrick · #14 7th April 2008, 12:54

You mean without any kind of valve? I think you'll end up with fuel vapour all over the place like I did with the standard valve. Maybe less so with a small pipe. I would put a valve in every time.

MartinClan · #15 7th April 2008, 18:12

Quote:

Originally Posted by Patrick

You mean without any kind of valve? I think you'll end up with fuel vapour all over the place like I did with the standard valve. Maybe less so with a small pipe. I would put a valve in every time.

The idea is that the breather would end up outside of the car or at least outside of the area occupied by people (low down at the rear of the fuel tank). If you add a two way valve it only stops fuel coming out when upside down. In normal operation it is just straight through, (as I understand), so just like an open pipe.

Or am I wrong here?

Robin

Patrick · #16 7th April 2008, 19:10

The valve I got lets more air in than out and has a ball in it for locking fuel in. There is a membrane in there so its more closed off the an an open pipe.

My previous breather when out under the back of the tank but there was still enough stuff going out on a slosh to waft up through the holes where the seat belts go through.

I think the risk with a completely open pipe is that the fuel will just vaporise and leave the tank and run out on a slosh (think siphoning). With the breather it only lets air out when it is under pressure - it not just open all the time. Get air out is more difficult than getting air in.

I'm just theorising