Fuel tank problem on 1.6TD

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Fuel tank problem on 1.6TD

Postby SYNCRO-VIKING » 03 Nov 2016, 16:36

Hello there -
I cannot fill my fuel tank properly.
Bought the car 3 years ago w 200,000 km, now 230,000 km, and I am sure back then I could fill the tank right up
for on the way home I did 800 km without adding any, so if 68 litres in the tank that would mean 11,7 km per litre
which sounds about right to me for cruising on the level.
Though even back then the fuel gauge needle never registered more than somewhere between 2/3 and 3/4 full.
This has got progressively worse and now the needle is halfway in the red sector even when there is diesel right
up to the top of the filler - at most I can get about 8 litres in at the petrol station BUT at home with a jerrycan,
with a much smaller diameter spout than the pistol used at the station, I can get about 15 litres EXTRA in...
Rocking the car side to side helps a bit but does not change the above situation.

And, in truth, I do not know how much of the diesel I am able to put in is actually available for the engine,
which is running perfectly normally, so fuel impurities such as diesel pest or other bacterial growth in an
advanced state can be ruled out.

As I understand it, the tank is shaped a bit like a "capsized camel" (ship of the desert - he-he), that is,
it is one tank but with a rise in the middle in order to clear the drivetrain, and presumably with internal
baffles with slits or holes in both sections to allow sideways fuel movement - yes?
Is something there clogged up maybe?

And in which half is the float situated? Presumably the section furthest away from the filler?

My mechanic says that to take the tank out is a MAJOR job and we would rather not do that.

He says there is a ventilation pipe running all the way around the tank - is this maybe blocked?
The car is now 24 years old (June 1992) so plenty of time for any dirt to build up.
Could this ventilation pipe be blown through with compressed air?

Any other ideas folks?

Thank you very much for your time,
Best regards,
VIKING
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Re: Fuel tank problem on 1.6TD

Postby garyd » 03 Nov 2016, 17:45

Hi,
having had my syncro tank out last winter I can offer a few observations.

Your description of the tank shape is close but the inverted 'hump' on the right side does not extend much below the central area level. The fuel outlet pipe is in the bottom of the left hand 'hump' and, on an injection engine vehicle (at least) will have an open topped 'tray' around it forming a swirl chamber to help avoid air being drawn into the pipework. There are no internal baffles.

The gauge sender sits above this in the left side end of the tank. The fuel return pipe which enters through the gauge plate extends about a foot into the tank and carries the gauge rheostat at it's end. The metal pipe may also have rubber pipe extension which curves down and pokes through a hole in the side of the swirl chamber.

The float arm pivots from the end of the metal pipe and so operates in about the middle of the tank.

If you look into the right hand rear wheel arch you will see a metal pipe about 40mm diameter running along the top of the chassis rail and behind the shock absorber. This is the filler pipe and it enters the tank low down through a rubber grommet seal. Above this pipe you will see a rubber hose of maybe 20-25mm diameter running at high level , above the shock top mount and connecting to the tank via a plastic spigot. This is the main air vent route and it connect to a spigot on the side of the filler inlet, just below the cap. You should be able to see the opening if you look into the open filler tube.

In addition to these there is also a system of breather pipes above the tank. There is a valved breather (closes in a roll-over situation) at each end of the top of the tank. These are joined together by hoses which loop back and forth across the top of the tank before 'T'ing together and running to just below the filler cap. Here it is open to the atmosphere. I don't believe that a blockage in this last system will affect the filling operation.

When I stripped mine I found that the large hose down from the filler to the metal pipe in the wheel arch has a severe collapse where it is enclosed in a metal sleeve behind the rear lights. This mainly because it is a fairly thick-walled hose and is forced to follow the curve of the metal pipe. Getting it out and pushing in a new hose was not easy. I ended up lubricating the outside of the hose with waxoyl (especially as the metal pipe had some rust) to help it slide in.

I have to say, though, that even with all new hoses I still have to fill very slowly after the tank is maybe half full. Parking the vehicle so the the filler corner is the highest point does seem to give some advantage but not a lot. I believe the problem it two fold. Firstly the design of the filler with the long horizontal section which was presumably done to avoid any conflict with the sliding door being opened during a fill operation.

However, I think the main cause is the change in formulation of the fuel which causes it to bubble much more than I remember it doing decades ago. I have also wondered whether forecourt pumps use air-lift technology given the amount of gas trying to get out of the tank filler.

Your point about the gauge readings is, I think, a different problem and probably electrical. I should take a look at the small, two pin plug on the metal mounting plate for the gauge sender. These can get very corroded so probably best to give it a good soak of releasing agent before trying gently to free it. Once off, check the conductors for cleanliness. Also check the resistance of the earth lead. Try connecting the two wiring terminals together and see what gauge reading you get.

If this doesn't change things, try with an empty/low tank, to remove the sender from the tank. Again, give a good wire brushing to the nuts and a good soaking for days before trying to undo them. There is a rubber ring gasket behind the plate and the studs are welded to two semi-circular strips which go inside the tank and poke out through the fixing holes. With this out, you can check if it is moving freely, what it does to the gauge, etc.

Also check the wiring connector to the dash insert to ensure that there isn't a problem at that end.

As you mention having a jerry can, you might consider ignoring the gauge and running the tank 'dry' before seeing just how much you can get in. Perhaps you are being mislead by the gauge and only using the top third or so of the tank? The one place where applying a compressor might help is the main air vent pipe accessed through the filler cap.

Hope this is of some help. Let us know if you get any improvement.
Garyd

1990 Transporter syncro camper
2 litre AGG 'GTi' engine
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Re: Fuel tank problem on 1.6TD

Postby jes*b » 03 Nov 2016, 20:47

I found a filler tube in my stash the other day I'll take some picks. To make the turns through the metal sleeve in the body the pipe has 'kinked' twice and even though it's been out of a vehicle a few years it has held that shape . The constriction is considerable. I cannot believe VW did not know this is what would happen to the pipe so logically it must have worked fine back in the day . The new frothy fuels are a nightmare. Especially in the Westy . Can take a good 20 mins to get a decent amount in .
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Re: Fuel tank problem on 1.6TD

Postby Aidan » 04 Nov 2016, 13:23

part of the issue is I believe the fuel stations have lowered the back pressure cut off pressure in order to minimise spillage which helps minimises staffing levels, they want the staff stacking the supermarket shelves when not taking money not being outside clearing up mess, margins on fuel are small, more money in selling the pop, fags and chocolate;
our tank wants a good flow into it but it does offer some resistance to filling compared to modern vehicles and we need to carry more fuel so notice the problem more
AIDAN
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Re: Fuel tank problem on 1.6TD

Postby SYNCRO-VIKING » 04 Nov 2016, 20:24

Thank you very much all 3 - but special thanks to Garyd, I shall copy this thread out and give it to my mechanic.
All the best my friends,
Keep SYNCing,
SYNCRO - 253 297 - 1.6TD - June 1992
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Re: Fuel tank problem on 1.6TD

Postby ninja.turtle007 » 04 Nov 2016, 21:45

I too have the same issue but when in Morocco the pump attendants easily fill to the top of the filler tube in a small amount of time.
Follow our overland adventure! http://www.resfeber.co.uk
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Re: Fuel tank problem on 1.6TD

Postby SYNCRO-VIKING » 05 Nov 2016, 17:21

ninja.turtle007:
AHA! Interesting! This seems to confirm what the others said about air-lift tech and different pressures, and maybe also lower spec fuels.
PS - I love Morocco and have spent a total of 2 years there on various long trips, backpacking, or with my old MB508D camper, or with a sailboat.
Wonderful warm and friendly people, fabulous scenery and amazing heritage.
Might take my Syncro there one day, inshallah - and you have now given me the perfect excuse!
SYNCRO - 253 297 - 1.6TD - June 1992
SYNCRO-VIKING
 
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Joined: 11 Sep 2013, 18:03
Location: Central Bulgaria (close to Paradise)
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Re: Fuel tank problem on 1.6TD

Postby jes*b » 05 Nov 2016, 19:20

This is the fuel pipe you can see where it creases to make the turns
Image
But worse still is when I put the pipe into something that approximates its route through the body the two creases really shut down a huge amount of the internal bore . Throw the new fuel in the mix and you are stood on the forecourt a very very long time .
Image
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Re: Fuel tank problem on 1.6TD

Postby SYNCRO-VIKING » 12 Nov 2016, 19:03

jes*b - thank you very much, and again to all of you.
shall report back whenever we do something about mine but I think it will have to be SOON...

meantime, if anyone has anything to add, please keep the good stuff coming,

all the best,
SYNCRO - 253 297 - 1.6TD - June 1992
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