Fuel tank venting

**beeRS** · 25-08-2021, 20:39

I’m fitting an aluminium tank in the boot. Where do folks run their vent pipes to? I’m guessing it has to vent outside of the car, but should the height of the vent be above or below the filler neck? I’d be interested to see what people have done.

**stevieturbo** · 25-08-2021, 21:00

Naturally it will have a rollover valve, so shouldn't really matter as such. But there is potential for a little mist to pass, so best to route it externally, away from exhaust and generally away from everything. Discharging low down would make sense.

Or go nuts and do an OEM recirc breather via a charcoal canister etc

**beeRS** · 26-08-2021, 04:13

Yes, I’ve got a roll over valve built in to the vent port.

My first thoughts were to run the vent through the boot floor next to the tank, or into the near-side wheel arch, but then someone threw me a curveball by saying the vent needs to be higher than the filler. I can’t see why that should be though.

**Graham** · 26-08-2021, 05:39

if you simply vent straight up out the top of the tank, the vent absolutely needs to be higher than the filler, otherwise if you brim the tank fuel will come out the vent.

a lot of race cars run the vent, up and then down through the floor below the tank level

**beeRS** · 26-08-2021, 11:34

Originally Posted by Graham

if you simply vent straight up out the top of the tank, the vent absolutely needs to be higher than the filler, otherwise if you brim the tank fuel will come out the vent.

a lot of race cars run the vent, up and then down through the floor below the tank level

That makes sense now. Definitely didn't want the vent poking out of a visible part of the body, but to loop it back down is a good idea.
I'd like to think the petrol pump would auto click off before the tank could fill to the brim though.

**stevieturbo** · 26-08-2021, 17:36

I've had mine vented out the boot floor for years.

With a proper rollover valve it is impossible for fuel to get out the top regardless of where that pipe ends up. If the fuel was to that level, the valve would be shut as the little ball inside would float to block it.

**beeRS** · 01-09-2021, 06:25

I've been trying to route my vent pipe so that it runs up and then down, but however I go about it, it just looks a clunky mess in the boot. Then I realised, that with a Newton Equipment TRV valve fitted, I can run the vent straight to the floor as stevieturbo says.

(http://www.newton-equipment.com/Arch...v66dimsnew.htm)

According to Newton Equipment...

"In the valve are two balls, one hollow plastic, and one stainless steel. If fuel enters the valve while the vehicle is cornering or braking, the hollow ball floats on the top of the fuel and moves to the top of the valve where it seals, so stopping fuel escaping. If there is a roll over, and the vehicle ends up upside down, it is possible that the hollow ball might leave the seat and allow fuel to escape. The weight of the stainless ball keeps the hollow ball on its seat, and fuel cannot then escape"

**rallyrob** · 01-09-2021, 11:19

Originally Posted by stevieturbo

I've had mine vented out the boot floor for years.

.
I had mine like that, pretty sure it never had a rollover valve in it either. It was higher than the filler too before dropping down and out the boot floor.
It was a Capri tank mounted on its side behind the firewall in a Mk1.
I'll be investing in a valve this time round though.