I am a bit confused on my gas tank. It doesn't seem to leak and I think the sender unit seal failed....anyways I am in the process of cleaning it out and I am stumped on putting sealer in it.

Tanks rust out over time, but none of them are "sealed" from the factory. How is it the factory produces a steel tank, paints the outside black, and ships it off with no surface rust inside??


upon removal I learned the XJS filler neck has a flap on it!! Mine has been rusted in the down position since I got it and I had no idea it was there!!

I soaked the feedpipe and parts in evaporust and now they look great. However, they already have some surface rust.

These aren't painted parts, WTF was on this steel and potmetal from the factory that prevents it from rusting for 10 years?

I'd rather not have a white sealer than can come on all over the inside of my tank, but If I don't it will rust. What the hell did they do that worked for so long?

 

My taking on this.

Production line supply from outside suppliers/manufactirers is on a "just in time" basis.

Once fitted in the car on the line, is basically sealed to outside air, and has a slosh of fuel added at some time on that line.

Once off the line, more fuel is added, usually not full, but enougfh for whatever is needed.

Why they rust from the inside out has been bantered as much as "how long is a piece of string".

Moisture is part of Gasoline/Petrol, fact.

Originally ALL new cars are used daily, and the tanks are kept FULL pretty much. Once the novelty wears off, that car becomes the "spare", or "hers", and usage drops significantly, as does the FULL tank scenario.

Moisture in the fuel, particularly the blended stuff, and the air gap above the fuel increase greatly, and surface rust starts. If/when the tank gets filled again, most of that rust is neutralised, until the tank is left part filled again, and the process restarts.


Same goes for the tank sender seal. Left OUT of contact fuel, it dries up, cracks, goes rock hard, LEAKS. Keep the seal wet with fuel and it will see the car out.

On our Diesel Road Train prime movers, there is a drain tap on each of the 4-6 fuel tanks, and DAILY drain off of water, and crap,about 1ltr, is mandatory. Refilling the tanks daily is also a MUST DO item.

Same goes for the air tanks for the braking system, drained daily, and the water that comes out of them is significant.

So, I suppose if we drained off the muck in the fuel tanks on a weekly basis, HAHAHAHA, the moiture would be less.

That is why the newer cars now have "plastic" fuel tanks and lines.

 

They're not 'sealed', but plated with a rust-resistant coating, zinc, nickel, cadmium etc.

My experience is that most auto gas tanks rust from the outside in, at least here where salt is used on the roads in winter.

 

okay, so the 3 tubes at the top of the tank are for venting aren't they? I blew through all of them just fine. Unless engine vacuum for some reason closes them off, i don't understand why my tank isn't venting, they were totally clear.

The excess pressure caused gas to leak out of my sending unit seal, this happened in such a way that the mat underneath was saturated. So much so that even after my gas was below that level, fuel still appeared to be leaking from under the tank. This is how it seems anyway, meaning I took the whole thing out and it actually wasn't leaking underneath. The stuff inside has killed 2 fuel pumps though, so I figured I may as well clean it out.
As if my car didn't smell like gas enough as it were

 

Being as how my market/conditions are way different to yours, take this as you may.

All my XJ-S's had odour of gas.

All my XJ-S's have had the tanks replaced, some under recall, others by me coz I found some NEW tanks a long while back.

That rivet that eventually protrudes thru the mat, and then the tank, caused 2 of them.

Rust from leaking rear window seal caused 1 other, at the lip that sits right up against the back seat panel.

The rest were replaced coz I had tanks on the shelf.

Those 3 pipes on the RH top side of the tank originally had hoses that went to the "tin can" vapour seperator tucked up inside the RH buttress, and forward to the charcoal canister in the LH front wheel well. This "can" quickly rusted out from what we were told, the fumes??.

All my cars have had the venting plumbing nightmare removed, and a SMALL 1/32" hole drilled in the tank cap. OK, some odour near the flap sometimes, but no more tank pressure/vacuam. The youngest of these mods is now 10 years since drilling, and no issues whatsoever.

If you have emission testing, DO NOT do this, as it will be frowned on badly.

As a side reason for doing what I did, most of the components I needed to put it right were listed as NLA (no longer available), so I made a decission.

All of the tanks I removed over a period were rusted inside form about 2/3rd upwards. NOT perferated rust, just bad surface rust, and the fuel in some had a real brown stain to it.

Finding a leak in them was/is hard, and pressurising them is tricky at best. I found 3 with witness bubbles at about 10psi, and it was the front seam in all of those.

Steam cleaning, scrubbing the inside of that tank, then a GOOD radiator shop, should be able to pressure test it in their water tank. It may take some convincing, but they can do it.

Short of that some gas in the tank, pluig teh orifices, pump it up with a foot pump, and slosh it around some. Sprinkle some talcum powder on the joints etc, which will turn cluggy when contacting gas.

 

thats the second person to tell me to just drill a hole in the cap.

I filled the bathtub and pressurised and didnt find any bubbles

 

all to familier with rusty tanks, 60yrs worth of ideas.

so when restoring my 78 XJS , i just jumped ahead of the problem areas.

NO rust ever again in my car, Plastic fuel cell(22 gal), stainless steel pump and filter, anodizied fuel ines with anodizied Aeroquip fittings, fuel rails billet aluminum, and stainless steel injectors!

what the hell,may as well do it 100%.

you know money is not important when it comes to our TOYS.

 

SS, there is a fourth pipe that exits that cannister and runs rearwards towards the back seat bulkhead a few inches, where it joins a very thin pipe (maybe 1/4 inch dia). This thin pipe runs along the back of the tank space behind the tank and exits down to below the car just in front of the chassis leg in front of the rear wheel. On UK spec models, it ends with a small barb and vents to the outside. On USA spec cars the barbed end of the pipe under the car is connected to the evap cannister in the LH front wheel arch.

You could try this, first disconnect the outside end of the pipe from any plumbing running forard to the front. The tank end of this pipe is unaccesible with the cannister connected by the three flexibles to the tank in place. If you remove that (not easy but possible if you unbolt and remove the boot side strengthener, ECU etc out of the way) you can JUST see the pipe to the outside. AND see the rochester valve that is in place in the flexible pipe between the cannister and the end of the 1/4 pipe. This valve (which is meant to relieve tank pressure/vac differences) is probably jammed shut and/or the very thin pipe blocked.

Now we get to the point. Once the inside end is disconnected you can blow through the thin pipe from the outside where you disconnected it from the front evap system. Also you can remove, click open and unblock the rochester valve, or replace it with a new valve. RGP recently posted a pic of a new valve he fitted to overcome this same problem. It will either let out of let in pressure once the difference is greater than a given amount.

Once this is OK, I believe your tank venting problems will be solved. You can leave the system in UK spec and no further problems! The pipe in question can be clearly seen in this shot, running along behind the tank, then upwards and then back towards the rear, ending in a flexible.


Greg