Fuel tank problem

[BJ75]

Hi there,

A year or so ago I bought a MK1 for my wife to putt around in, and a while after we bought it we found it would start crapping out intermittently. Starts running rough, then rougher, then starts to cut out, then cuts out completely. Leave it for 5 - 10 minutes, start it agian, and it will run fine for a while, then the cycle starts again. Eventually it lasts less between crap outs. I did notice a large amount of air/bubbles in the fuel filter, which I've searched about here and read several theories as to it's cause. However, the difference here is that the air was making me suspect there might be a leak somewhere closer to the tank, which might explain the intermittency, and explain why it gets worse as time went on. So we have figured out if we keep the tank full, and fill it up every 50km, then the problem never happens.

I took it to my local mechanic (who I trust, but has openly admitted to not being a Golf expert), without mentioning my theory, and he came up with the exact same one. He thinks there might be a crack in the fuel line inside the tank, likely up high. However he said replacing the tank is very costly from a time point of view as it has to come out from underneath?

Anyway, I just wanted to check with the MK1 experts on here whether they agree it is a problem with the fuel line exiting the tank, or whether its more likely one of the other "air/bubbles in fuel filter" problems I've read about here (fuel return line, leak in hose near clamp etc).

Thanks.

[Oneofthegreats]

G'day BJ45 & welcome to the forum.

Before I'd go changing fuel tanks (which really isn't that hard to do if you've done one before) I'd be swapping over fuel caps.

The valves inside them which allow the tank to empty without causing a vacuum can s#%t themselve's & cause the tank to try & suck in on itself (it can't though because it's steel) & starve the engine & fuel pump of fuel.

Easiest way to explain it is how a jerry can empty's it's self without a breather & then you open the breather & walla. Nice flow.

Need to know how long does the car run for before it start's to run rough? If it isn't that long it maybe a fuel pump.

Also post up your location to.

[BJ75]

Thanks golfworx, I'm in Melbourne.

That makes sense what you said about the fuel cap. I may check that out before I do anything major, if I don't get any more specific things to target. I suppose I could test it by turning the car on, leaving it for 5 - 10mins at idle, then removing the cap and seeing if it sucks a whole lotta air in yeah?

As for how long it runs - the car will first start to misbehave after about 60 - 70km from fill-up. If it dies at this point (which happens if you don't start driving slowly to fix it, or if you hit a steep hill), just turning it off for longer than 10 mintues does the trick, and it will start up again and run fine. From here until about 100km, it will die every say, ... 10 - 15km. Then this gets worse and worse to the point it only lasts a few hundred meters before conking out. The air/bubbles in the fuel filter seem to get worse as this progresses as well. I think the worst we saw it was at about 140km, and this is what was happening. It was at this point I figured the rate of progression of failure seemed to mirror fuel consumption, so I headed (crawled) to a servo even though there was over half a tank on the dial.

Then, as soon as you fill it up, it runs fine again, and the amount of bubbles in the fuel filter goes back to very little, and the above cycle starts again.

As for replacing the tank - I'm sure I could manage it. I used to work on cars all the time in my teens/early 20s (bit of a Datsun fan). I got sick of knuckling my fingers on engine components, and always having something just slightly wrong that I'd have to fix myself, so I started buying new cars once I got a real job (read: boring, un-inspiring office job that pays well). However I like the idea of tinkering with this Golf a little - just to keep it happy. I still have all my tools ... so I may tackle it myself (if it's the tank that's the problem, that is...).

[Oneofthegreats]

I reckon you'd be better off taking it for a drive & wait till it start's to happen, then remove the fuel cap & see how it goes.

You're no going to burn up enough fuel sitting at idle for 5-10mins to create enough vacuum to cause this problem.

[hazards_golf74]

i had the same problem i blew the fuel line backwards problem fix (with an a gun)

[BJ75]

So do you mean get an air compressor with a gun, undo the fuel line on the intake side of the fuel filter, stick the nozzle of the gun into it and blow air back into the tank? I remember doing that with my old Datsuns back in the day but I can't remember what the reason was for doing it?

In any case, I'll give it a go. I've been meaning to get onto this for months now, but the fact that keeping it filled up works fine kinda reduces the urgency.

A search here for problems similar to mine has found references to fuel return lines being a cause of the problem, as well as the fuel lid golfworx mentioned above. Think I might do a bit of tinkering this weekend since the mountain bike is in the shop.

[smithy010]

In my experience, it is the little strainer on the end of the fuel line (in the fuel tank) getting blocked up with crud. I had the problem you mentioned, and couldn't find it for months and months. Ended up, that's what it was.

Remove the pickup line, and get rid of the little strainer. But ensure you have quality filters up the other end.

[BJ75]

Remove the pickup line, and get rid of the little strainer. But ensure you have quality filters up the other end.

Thanks for the tip. Now, I'm not completely inept at working on cars and should be able to figure this out, but it has been a while so any extra help will be handy - is there anything special about removing the pickup on the tank of one of these things? I'm assuming it's under the back seat?

[Golf Loon]

Under the back seat, there is a little black panel with 3 phillips head screws. Remove that, remove the sender from the top of the tank and reach in to the right with longnose pliers and pullout the strainer.

[BJ75]

Thanks heaps for your help everyone. I'll be tackling it this weekend. Looking forward to getting the hands this kind of dirty for a change (as opposed to the chain lube, grease, mud & grime I get working on the MTB).