Twin Fuel Tanks Teaser

[Avroflyer]

Now then, here's a teaser.

NEO is a 1990 400SE. I fill the car to full and can never get more than 30 litres in. Fuel gauge shows full so off we go. 160 miles later of sedate motorway driving and gauge says "need more fuel", bouncing between zero and a quarter, so pull in for fuel and hmm - can only get in 28 litres. Good news is reasonable fuel consumption, bad news is what has happened to the nearside tank? It's as if the LH tank has been disconnected. The gauge in mounted in the RH tank and seems to react to the RH tank only. Having a good look around undeerneath yesterday, though, I noticed that the fuel return line from the injector rail, is connected to the nearside (LH) tank. So where's it going?

One thought is that the bottom feed from the LH tank to the swirl pot is blocked and the LH tank is permanently full, with the recirculated fuel spilling back into the RH tank through the top interconnecting pipe(s). That would be a real pain to empty!

Has anyone had this problem? Frequent fill-ups are a pain but manageable; however I don't want a gout of blockage from the LH tank suddenly splurging through the swirl pot and into the fuel pump, so I must do something about it whilst she is laid up for a radiator and thermostat change.

Cheers

[Solitude]

Could be a lot of sh**e in the line to the swirlpot.

If you have an older swirlpot it will have a filter in it (new ones don't so a pre-pump filter is required)

Blockage could be in the tank as i don't think they have much of a filter either.

Sounds like a bad gauge/switch ??

Or maybe its half a tank on the motorway !!!!!!!!

[mrzigazaga]

Hi Mate..I doubt if its blocked anywhere as you would be getting running issues..Perhaps your fuel sender is faulty..I guess the only way would be to wait until it is reading 1/4 of a tank and then drain the tanks down to see what is left in them..make sure you have a very large container handy, Just in case...I wouldnt drive it to see as you dont want to pull any crud through..Ziga

[adam quantrill]

The two tanks are connected by a big rubber pipe aren't they? So a blockage would be almost impossible.

My money is on the sender, take a gallon of fuel in the boot and run it down till it starts to cut out, ignoring the gauge.

You should be able to get 61 litres in although mine rarely gets lower than 8l before it starts misbehaving, so around 53l on a refill to the neck.

Also I must say that if you let the filler cut out on the first click you are missing out on between 5-10l of capacity.

[RCK974X]

adam quantrill said:

The two tanks are connected by a big rubber pipe aren't they? So a blockage would be almost impossible.

On my 2.8, the tanks are connected AT THE TOP by a big pipe, but for fuel delivery they have only the standard smallish (1/2" ?) pipe connected to a 'T' piece and then to the fuel pump. One of the fuel pipes on mine was partially collapsed, so I replaced it. So it's possible to get one pipe gummed up, but I agree it's far more likely to be the fuel sender.

It's worth checking the fuel pipes look OK, just to make sure ....if you want to be totally sure, disconnect and drain the tanks to make sure there's no crap at the bottom - it's not common, but it does happen !

[Wedg1e]

I had a similar issue with my Esprit: fuel gauge said 50% but the carbs ran dry!
Turned out to be a big blob of silicone sealant (dunno why the hell it was in the fuel tank) blocking one tank outlet; the sender was in that tank so it looked like the car had fuel but the other tank had been drained.

[Grady]

I have the same issue. The gauge is correct - for 1 tank. If the gauge say empty, it's out of fuel; and when it reads full, no more goes in (max is about 7.5 gallons). Even if there was a major blockage in one tank (such that it wouldn't fill on fueling), I would think the tanks would equalize overnight but no.

I had the hoses replaced - my shop hated me for that- but they missed the part about checking if both tanks were filling and both drains were clear.

I've gotten use to cheaper fill-ups, but one day... Grady

[Campbell]

There is a very good chance the pipe that connects the 2 tanks is kinked as it bends up over the.prop.shaft. I did mine a few years ago it is 1" replaced with a custome made bradded stainless steel item incase it ever touches the shaft but i know some cars only have 1/2" pipes. The fuel return goes to the left tank so you are getting some thing between them. I would have the lot replaced and im sure you will see a difference.

Cambelt