Fuel tanks and guage

[jeff m]

I think my fuel guage is getting worse.
It starts approaching zero, go fill up, can only get 6 gallons (US).
13 gall capacity ?

I know it is said it takes a while for it to move over to the other tank, but petrol should move quite easily across as the conn hoses are a decent size.
In the past I've seen it move quite well even on just a loose fitting

I've never really checked my mpg as I've never been concerned with cost, but now I'm getting concerned because of range, I don't want to run dry, not a good idea with CIS injection (it's a 280).

I now find my safe range is about 100 miles, most of it spent watching the guage, not much fun.

Anyone had the sender out of their tank ??
If it's "drop the rear" I'm going to get a dipstick

[Grady]

Jeff - I've had the same problem and over the years there have been numerous threads on this. IIRC many have the same problem, a few can fill both tanks.

Considering there are 3 cross-tank hoses, it seems hard to believe they are all completely blocked. The tanks ought to equalize over time (like overnight).

Somewhere on the driver's side tank there is a air vent. I've never found mine but I have to wonder if the vent has a one-way valve that's stuck closed is it creating a giant air bubble in the driver's side tank?

Maybe someone who has had their body off could shed some light. Grady

[SEvans]

IIRC the only vent for the tanks is at the top of the O/S tank near the filler. A pipe runs from the tank around the back of the boot and out of the floor. I suspect if this got blocked you could have some problems with air locks.
On my tank the filler pipe runs across the top of the 1st tank and out the other side, this is where the thick pipe joining the 2 tanks is connected. Inside the tank the thick pipe has some holes in it, so when filling the tanks some petrol goes into the first tank, through the holes and some petrol passes straight through the first tank and into the second.
The petrol sender for the gauge is mounted on the inside of the O/S tank. On my car (with trailing arm) it is possible to remove it without removing suspension etc. You need to make a note of it's orientation, as it's possible to get it back in just a few deg out. Cheers Steve

[adam quantrill]

The sender is likely got a worn out track, which I think is just a wound coil of resistance wire.

So I suppose you could repair it reasonably easily.

However, it might be the gauge. I has an intermittent problem which turned out to be the internals of the gauge, one wire wasn't soldered down at all. I took it to bits, soldered it, and reassembled, and it's been fine ever since.

As for filling the tanks, yes there are pipes at the top and bottom, so you should never have a problem filling them, apart from speed. The tanks have 60-odd litres of capacity. If you're worried about running out, keep a gallon of fuel in the boot and a suitable funnel. When I had the gauge problem I just dead reckoned from my mileage, and besides you can usually tell when you're on the last gallon because under acceleration the engine hesitates.

Don't forget that any sports car has no 'crud in the bottom of the tank' when you get close to running out, because the cornering mixes everything up all the time.

[blaineuk]

thought there was a breather on nearside tank but not sure now, will have a look at the weekend, pipes are to big to block up, just fil it slowly and you will get more in.

[grahamw48]

When I got my first Wedge (Series 1 FHC) it had the Jag style twin fillers,
and if a cap wasn't properly fastened, as you were filling from one side, fuel would come shooting straight out the other !

Expensive on fuel, and embarrassing at the petrol station.

I soon got the hang of it.

[jeff m]

Thanks guys, I did do a search before posting but your answers are better than the prev threads.
I've just got a diag of the fuel system (for the US 280) there are two pipes across the top of the tanks, but the pipe across the bottom does not link the two tanks directly they both go into the anti surge pot/filter hence the slow filling of the second tank.

I hope there is a good tech reason for that

There are also two breathers from the filler neck (RHS on a LHD)one of them has a rollover valve.

I was going to have a go at this today but my bottom hose got a pin hole and that had to take priority. The hose had rubbed on lower steering UJ (bu66er) that's changed now though. (wasn't easy)

I think I may change the swirl pot/filter first, then attack the rheostat/sender if it does not behave in more reasonable manner

[jeff m]

Below is the diag for a US 280 (veiw from front of car)


Mods, not sure if there is a copyright prob here, delete if there is (and sorry)

[Grady]

Is there any one-way valving in a swirl pot? My understanding from prior threads is the pot is just a gravity fed accumulating tank with an internal screen filter. If that's the case, then assuming some air equalization at the top of the tanks via the hoses, the tanks ought to equalizes from the bottom. (Boat tanks do.)

My gauge has always been consistent - and maybe consistently wrong. 1 full tank is about 7 gal (rating for one tank = 7+ gals IRRC) and it drops in a linear fashion between full to empty depending on use. The most I ever eased in with a slow fill and a long wait was almost 8 gal. I assumed I was just working off one tank (the one with the filler) most of the time.

BUT if the sender is in the (US) drivers side tank - then I'm actually filling the far tank - not the tank with the filler. Most perplexing!

And not fun to try to work up in there without removing the body, birdcage or rearend while playing with petrol