Inside the fuel tank...

[cycloneracing]

I have pulled out my fuel tank (VC commodore Sedan) because it is leaking. I searched some old threads and it is leaking the same place as ari666’s was and I intend to weld it up like he did (that thread was from November 2011).
Typically all the rubber hoses for the breathers are deteriorated and basically crumbled in my hands. So I have to redo all of that.

Now the thing is: inside the steel tank, there is another smaller plastic tank/thing clipped to the upper half of the tank. This plastic tank/thing has two plastic pipes coming off if and they look like they connect to the two little steel breather pipes that emerge from the top of the tank on the outside.

1. What does this plastic thing in there do? Is it some kind of surge component? It must have something to do with the breather tubes?
2. Where the steel pipes enter the tank, and the plastic pipes join to it, there is a rubber hose that connects the two, and that is all broken and I fished it out of the bottom of the tank. With only the float hole to view inside the tank… how the hell do I get in there to fix this all up? How do I put new rubber hoses in there to connect the two?

I am not sure if I have explained this well enough, I can’t take a pic till tonight, but I will try to post a pic up later…

[ari666]

mate. i hate to say this, but you may as well look at a replacement tank from the wrecker. i only welded mine up as a VERRRRRY tempory fix. what will happen now is on the inside of the tank next to the welds, itll start to rust (the welds will have brned off all the rust protectant they put in there). and because petrol floats on water, any moisture that gets in there will get trapped and sit on the bottom of the tank, right on top of the welds. so i reckon i have about 6 months before itll start weeping again.

i scored a crappy tank from the wrecker for 50 bucks. its just a matter of getting it home from work and cleaning it up.

[cycloneracing]

The rest of the tank is immaculate though. You can get stuff from Rust Stops Here - Paint - Tank Sealer - for rusty surfaces - KBS Coatings to put in the tank to seal it all up on the inside. It is about $96 though - cheaper to get another tank I guess...

I reckon what will kill it for me is those pipes inside - I have no way to connect them up again. I don't even know what they do!

[Drewie]

I had the tank on our VC repaired about 6 or 7 years ago by a radiator repair place, ours sprung a leak in the middle of the tank at the lowest point, every secondhand tank I looked at had rust forming in the same spot, how they repaired mine was they cleaned up the area and laid a bed of molten solder then placed a
4"x 4" square metal patch in the solder then soldered around the 4 edges, touch wood it has held together for all these years. Our tank was quite good except for a small rusty bit in the middle.

[cycloneracing]

OK here are some pics of inside the tank:
This is where the breather pipes go from inside the tank to the outside:


This is the hole in the tank. It happened where the pick-up has been rubbing on the bottom of the tank, exact same spot as ari666:


This is the end of the larger breather pipe, and you can see that plastic swirl tank thing that is inside the tank:


And this is where the two steel breather pipes end inside the tank. There are two plastic pipes in there as well, and I am sure they are joined together by a rubber hose part, that has fallen off due to age and deterioration:


So yeah, not sure how I am meant to join those pipes all back up again when I can't get in there!

[Drewie]

Maybe don't worry about them and just put a vented petrol cap on. We have a vented cap on our VC, the VC is after all 31 years old and half the pollution gear doesn't work anyway. I can't remember exactly but I have feeling the tubes inside our tank on the VC may have been broken, was about 6 or 7 years ago I had it repaired, so a bit uncertain. From memory we vented the cap as it used to get a lot of vacumn in the tank we used to get a big rush of air when you removed the cap, with the vented cap we have never had a problem since, I can't recall if we vented it before or after the tank repair.

[vkberlina]

On my original VK tank I got a couple of holes, ex country car traveled down many dirt roads saw the underside sandblasted daily, I soldered mine up with a high powered iron and loads of flux.
There are sealants you can buy to seal & rust proof the inside of the tank so it wont rust, if you cant find them on the net, go to a small auto parts shop like bullseye etc and they should be able to help.
As fro fitting hoses to the inside of the tank I dont remember there being any in my tank but you can buy really long nose & handled long nose pliers which might do the trick or find a half useful teenager or kid to help you, their hand should fit in the tank

scott

[VK SL 3800]

Can someone tell me what the plastic tank is? All the tanks ive seen have the metal breather lines just going nowhere across the top to the other side and any EFI tank has the swirl pot on the bottom.

[cycloneracing]

Can someone tell me what the plastic tank is?

Yes I can tell you what it is. I Finally got back onto sussing this problem out.

The three pipes entering the top of the tank are all vent lines. The larger diameter pipe is the "fill ventilation line" and connects the upper area of the tank with the filler neck. This is used only when filling the tank with petrol.

The two smaller diameter pipes vent the left hand front and left hand rear corners of the tank together with the fill limiter pot.

So the plastic tank is the fill limiter pot. It has a capacity of 3 litres and is located inside the fuel tank. The purpose of the fill limiter pot is to provide fuel overfill control by maintaining a guaranteed air space in the tank to allow for expansion of the fuel. The fill limiter pot has a 1mm hole on the underside to allow fuel to expand into the pot and then drain out later.

So, the two plastic tubes inside the tank should be connected to the metal breather lines, for sure. The GMH manual states "For practical purposes, the fill limiter pot is part of the tank and no service work is possible on it." So even GMH concede that nothing can be done inside the tank.

This is all great to know but I still have not sorted my fuel tank problem and it is still out of the car... Will have to get a VN-VS one and see if I can make that work...

[vkberlina]

just to add
I was at the paint supply place the other day and they have a product called Motor cycle tank sealer kit, made by KBS I have seen it used on a car tank when they had a problem with it rusting inside.

scott

[cycloneracing]

...they have a product called Motor cycle tank sealer kit, made by KBS...scott

KBS have a car kit as well, or you can but it in the 1/2 litre tins, the bigger the fuel tank the more tins you buy.

I would use this if I had a fuel sump welded into the tank. You would have to be careful that it only spread out on the lower half of the tank though, if it blocked up the breather pipes and the fill limiter pot 1mm hole then the whole ventilation system would not work.

hmmm, I wonder how much a custom alloy drop tank costs...

[vkberlina]

Prob be better off buying a couple of sheets of alloy and a welder and making up 2 or 3, selling 1-2 and making back the difference in the costs and still having the welder and a tank

Years ago I split a tank about 10mm below the seam welded in 30mm strip, extended the fuel tank float arm so the fuel guage was accurate and welded up the tank after cleaning up the welds on the outside I used a KBS kit to seal the insides of the welds.

Now I would just use a VN/VQ etc big tank

Scott

[Drewie]

When we had our VC tank repaired I can't recall whether there were any plastic bits in the tank or not, however I did replace some of the hoses, we did have a bit of an issue with the tank creating a vacuum like as in when you removed the cap there was quite a rush of air, we just popped on a vented petrol cap and have not had any issues for the past 7 or 8 years. If the bits you are concerned about are only for venting the tank I wouldn't worry too much and just use a vented petrol cap and maybe don't overfill the tank. I think the main thing the hoses do is let the fumes go into the charcoal canister in the engine bay and when you start the car it purges the canister and burns the fumes so no fumes escape into the atmosphere, all part of the emission controls. Half the emission stuff on these old cars probably doesn't work properly anyway.