Fuel Gauge help! Put fuel in - still reading empty

[shortlad]

Just had a strange one at my local BP station.

I was reading 13 miles on the range and the fuel light was on.

Pulled into the petrol station and put fuel in and then paid. When I got back in, instead of the usual reaction of the gauge and fuel computer they stayed where they were pre fueling.

I switched off the ignition and switched back on again. I went back into the shop and asked if it was physically possible to get no fuel and they assured me that it was impossible as the pump works on the fuel passed into the car.

I drove off thinking it may reset and it didn't. I got to the car park at work and switched off again and left it a few minutes and turned back on again and the same.

Next I reset the full trip computer and still the same fuel reading.

The mileage is going up so that part is working as is the rest of the dash.

Does this sound like a fuel sender? Has anyone else experienced this?

Should have said.... 2003 911tt

[993AL]

Did you fill the tank or only put a small amount in? this is common if you only put a small amount of petrol in.

[willfinch36]

Put in more.. I had the same issue when I ran low once!

[shortlad]

993AL said:

Did you fill the tank or only put a small amount in? this is common if you only put a small amount of petrol in.

I put 25 liters in as I'm not using the car much at the mo and it's going to be SORN for January and probably February.

Can it really just be this?

So if I fill the reat of the tank it will cure the reading issue?

[willfinch36]

Yup.. another £20 should make the difference...

[markiii]

I'm told the tank is a saddle tank and the lowest fuel level is below the float level.

So yes seems possible, mine does the same

[993AL]

shortlad said:

993AL said:

Did you fill the tank or only put a small amount in? this is common if you only put a small amount of petrol in.

I put 25 liters in as I'm not using the car much at the mo and it's going to be SORN for January and probably February.

Can it really just be this?

So if I fill the reat of the tank it will cure the reading issue?

Yes, sounds like you just need to fill up.

[shortlad]

This is a strange one.

I thought a fuel gauge had to work from a float for the whole tanks as the amount of fuel used can vary alot over the use of 1 full tank due to changes in driving conditions that could take place. If this is the case surely a guage should measure all of the time no matter how much fuel is in the tank?

This seems to suggest that below about 25 litres it doesn't measure the fuel level but guesses it based on the useage of that tank so far.

Am I missing the point?

I know it's an easy case of just going and putting more in but I like to fully understand these things

[mankey]

I've experienced the same thing with a courtesy car, obviously not wishing to overfill. Would have thought that 25 litres should make a difference and tip the scale.

[SteveM46]

shortlad said:

This is a strange one.

I thought a fuel gauge had to work from a float for the whole tanks as the amount of fuel used can vary alot over the use of 1 full tank due to changes in driving conditions that could take place. If this is the case surely a guage should measure all of the time no matter how much fuel is in the tank?

This seems to suggest that below about 25 litres it doesn't measure the fuel level but guesses it based on the useage of that tank so far.

Am I missing the point?

I know it's an easy case of just going and putting more in but I like to fully understand these things

Are you sure you didn't put the fuel in someone else's car? It's easily done

[993AL]

shortlad said:

This is a strange one.

I thought a fuel gauge had to work from a float for the whole tanks as the amount of fuel used can vary alot over the use of 1 full tank due to changes in driving conditions that could take place. If this is the case surely a guage should measure all of the time no matter how much fuel is in the tank?

This seems to suggest that below about 25 litres it doesn't measure the fuel level but guesses it based on the useage of that tank so far.

Am I missing the point?

I know it's an easy case of just going and putting more in but I like to fully understand these things

From the handbook-

"If the tank is nearly empty and you top up with only a small quantity of fuel, this cannot be registered by the level gauge and cannot be used to calculate the range on remaining fuel"

It doesn't say why.

[markiii]

shortlad said:

This is a strange one.

I thought a fuel gauge had to work from a float for the whole tanks as the amount of fuel used can vary alot over the use of 1 full tank due to changes in driving conditions that could take place. If this is the case surely a guage should measure all of the time no matter how much fuel is in the tank?

This seems to suggest that below about 25 litres it doesn't measure the fuel level but guesses it based on the useage of that tank so far.

Am I missing the point?

I know it's an easy case of just going and putting more in but I like to fully understand these things

exactly that

[SteveM46]

This is completely beside the point, but reminds me of a story I once heard Bob Monkhouse tell on TV. No really, it's good - stay with it!

Apparently a chap lived across the road from Bob's father. This chap was always very proud of his cars, always felt his car was better than everyone else's and was always putting down the other residents and the cars they drove. He was a complete pain in the a**e. Anyway, one day he bought a brand new car, and was quickly telling everyone how wonderful it was, how it had amazing fuel consumption and would be so much cheaper to run than anything else in the street.

So Bob's father decided to play a trick. Each evening, he sneaked over the road with a petrol can, and topped up this chap's car. After a couple of days, the chap was still crowing loudly about his new car, about how many miles he had done without using hardly a drop of fuel. And after a week of this, the chap was completely beside himself, that he had driven his new car for a week, and that the fuel consumption was so amazing that he hadn't even had to fill it up. He wouldn't stop talking about it, and made sure everyone in the street knew how clever he had been picking such an amazingly economical car.

Then Bob's father stopped topping up the tank. And this chap became very perplexed and bewildered. He watched the fuel gauge plummet, and he could not understand how his car, which had used almost no fuel in a full week of driving, was suddenly getting through fuel at a 'normal' rate. And within a week he was a broken man.

Good trick!

[shortlad]

SteveM46 said:

Are you sure you didn't put the fuel in someone else's car? It's easily done

If I did they have fuel in their engine compartment

[JW911]

markiii said:

I'm told the tank is a saddle tank and the lowest fuel level is below the float level.

So yes seems possible, mine does the same

They all do that, sir.

If in doubt, read the instructions. The owner's manual says a minimum of 30 litres from empty is required. I made this mistake myself once.

[BrewsterBear]

I've done this in my C4S. I was running low and didn't want to risk it, but the station I was passing didn't have super so it was just a splash and dash to get me to my usual Shell. I put over two gallons in, but when I started the car it still showed the same distance to empty and same level on the gauge. It did make me wonder wheher the pump had actually delivered anything.

[Diesel130]

shortlad said:

I put 25 liters in as I'm not using the car much at the mo and it's going to be SORN for January and probably February.

IIRC isn't it better to leave an unused car with a full tank, so that you don't get condensation build up in the air-gap. Think that was the reason - or maybe I'm talking a load of bullst.

[mollytherocker]

This is due to the 4wd system at the front. The float only reads/works on the top half of the tank, the rest is a calculated guess!

When you fuel it, you need to register the float half way up otherwise it doesnt know you have fueled it.

Crazy isnt it!

MTR

[anonymous-user]

mollytherocker said:

This is due to the 4wd system at the front. The float only reads/works on the top half of the tank, the rest is a calculated guess!

When you fuel it, you need to register the float half way up otherwise it doesnt know you have fueled it.

Crazy isnt it!

MTR

Molly is spot on - happened to me a number of times. And the other moral of the story is don't depend too much on how many miles the car shows you have left. It's a bit of stab in the dark, albeit one that errs on the side of caution.

[Trev450]

Diesel130 said:

IIRC isn't it better to leave an unused car with a full tank, so that you don't get condensation build up in the air-gap. Think that was the reason - or maybe I'm talking a load of bullst.

It depends on how long you are leaving it for as fuel does go off over time.