997.1 GT3 fuel tank question..

[vallance5]

Having read the owners manual the GT3 claims to have a 67 litre tank for RHD and 90 for LHD cars. If I run my car to zero on the computer and with the needle reading all the way at the bottom, when I fill up the most I can get in is about 41 litres.

Took the car to OPC where I got it from and they said the reason is because its a "saddle tank" and the computer and needle dont register the two bottom compartments of what ever it is straddling.

Havent seen the tank so dont know if this is true, can anyone verify?

However I find it hard to believe that Porsche designed it in a way that a third of the tank is totally unregistered by the computer and fuel gauge.

Does anyone have any info on this or other GT3 owners confirm they have the same problem?

Thanks in advance.

Edited by vallance5 on Wednesday 27th March 15:27

[Magic919]

If they are using the AWD chassis, then this makes sense. C4S owners complain of this from time to time. Not saying it's a wide body.

[MadMark911]

Nope - I've managed to get £85 (or just under 60 litres) of Shells finest Super Unleaded in the tank .... emptyish to brim full!

[james S]

Yes I got 58 in mine last wk

[vallance5]

james S said:

Yes I got 58 in mine last wk

What was the computer and needle reading?

[twonames]

Never had that problem - can usually get at least 60 in. But if I put 20 litres in when almost dry (i.e. to tide me over to the next V-Power station) it doesn't register at all when I start it up again.

[vallance5]

twonames said:

Never had that problem - can usually get at least 60 in. But if I put 20 litres in when almost dry (i.e. to tide me over to the next V-Power station) it doesn't register at all when I start it up again.

How do you know when its dry? Does the computer say 0 miles remaining and you keep running beyond that? Im guessing so if you are saying it still doesn't register after you put 20 litres in.

[Magic919]

I think we've established that, as Porsche say, the bottom 'half' of the tank will not register on the gauge. This is the same on other 911s that use the AWD fuel tank. The computer just guesses.

[vallance5]

Pretty major flaw that you have to guess when you have used the other 20 litres of fuel especially if your going on long journeys.

[Magic919]

As you can see here, most people cope though. We had a 996 C4S and never got stranded or had problems filling it up. Same arrangement.

Your tank is either never empty or never full. Would be worth experimenting to find out which.

[vallance5]

Done some more reading and seems like this was a problem on the 4WD models like you said. However the issue for them seems to be the gauge not registering that they have added more fuel if they do not fill up more than half way, or above the saddle shape. People have talked about re-calibrating the gauge by disconnecting the battery and Porsche even did a recall for this on 996 models.

Does that mean the GT3 uses the 4WD cars tank?

Edited by vallance5 on Wednesday 27th March 17:45

[pete]

vallance5 said:

Pretty major flaw that you have to guess when you have used the other 20 litres of fuel especially if your going on long journeys.

No, no, no - not that big an issue. When the tank gets down to 20 litres or so remaining, the gauge stops using the float in the tank, and instead uses the last known tank reading, less the reading from the computer about how much fuel is being consumed by the engine. That uses the same mechanism used by the OBC to give fuel economy, which isn't based on the fuel tank float; it's probably based on a calculation from injector cycles or something!

So the upshot is that despite the approximation, the gauge and remaining range is always pretty much accurate, *as long as you have put enough fuel in the tank to reset the float*. That was around 25 litres from empty from my experience of my 7.1 GT3. You never have to guess about the last 20 litres; the car does that pretty accurately for you.

If you can only get 40-odd litres in when the computer says you have 0 miles remaining, you have another problem.

Pete

p.s. Yes, the GT3 uses most of the 4wd floorpan, along with the tank, despite still having the narrow body on top. It's more rigid than the 2wd shell apparently.

Edited by pete on Wednesday 27th March 17:48

[vallance5]

pete said:

No, no, no - not that big an issue. When the tank gets down to 20 litres or so remaining, the gauge stops using the float in the tank, and instead uses the last known tank reading, less the reading from the computer about how much fuel is being consumed by the engine. That uses the same mechanism used by the OBC to give fuel economy, which isn't based on the fuel tank float; it's probably based on a calculation from injector cycles or something!

So the upshot is that despite the approximation, the gauge and remaining range is always pretty much accurate, *as long as you have put enough fuel in the tank to reset the float*. That was around 25 litres from empty from my experience of my 7.1 GT3. You never have to guess about the last 20 litres; the car does that pretty accurately for you.

If you can only get 40-odd litres in when the computer says you have 0 miles remaining, you have another problem.

Pete

Thanks for the info.

Personally i think im having a separate issue from what other people are describing. As I say the needle is all the way down and it says 0 miles remaining. I then go and fill it to the brim and only get in about 40 litres.

[james S]

vallance5 said:

james S said:

Yes I got 58 in mine last wk

What was the computer and needle reading?

Right down about 30 miles range

[fioran0]

with GT3s, all RHD 996 and 997 use a 67L ( or thereabouts) fuel tank the same as that on the C4. this has saddle bags as it was originally designed to clear the front diff on the 4wd cars. as a result the float to measure fuel cannot measure to the bottom of the tank. to compensate the lower portion of the tank is "estimated" using the onboard computer. this is why if you run the tank down and dont refill all the way that the fuel cage doesnt register you having put anything in at all.
this calibration can go off if theres a problem with the tank, sensor or cluster. it shouldnt go off from only having the battery disconnected but it is possible.
if you cannot get enough fuel in then the first point of call would be to have the system recalibrated. this involves draining the tank, refilling with a known amount then telling the cluster via the porsche system tester.
you may have other problems like a blocked vent valve or similar but start with the calibration.

LHD cars had the option to run a larger 90L tank. this utilised the space where the diff would be to increase the tank capacity. these tanks do not need calibrated as they have no saddle bags. there is no 90L tank available for RHD cars. the tanks are shaped to clear the steering column position and since all porsche race cars are LHD porsche did not make a larger tank for a rhd shape.

the factory race cars until 2002 were delivered with a 64L tank (though a 90L could be bought) however this was the same shape as the C2 tank (ie without saddle bags) rather than the C4 style and didnt need calibrated. from this point onwards the 90L tank has just been standard fitment.

Edited by fioran0 on Wednesday 27th March 19:24

[fioran0]

pete said:

p.s. Yes, the GT3 uses most of the 4wd floorpan, along with the tank, despite still having the narrow body on top. It's more rigid than the 2wd shell apparently.

this is incorrect though its repeated everywhere. the GT3 uses the front trunk firewall from the C4 but it offers no additional strength benefits. FIA rules prohibit a fuel tank to be placed, or extend beyond the front axle. the only way porsche could provide a required 90L tank for endurance racing was to use the C4 front firewall and extend the tank to include the space used by the diff on the C4. this kept it behind the axle and got the required capacity.

Edited by fioran0 on Wednesday 27th March 19:32

[pete]

I stand corrected! The truth is far more interesting than I thought :-)

[V8KSN]

Sorry to bring up an old thread but for anyone searching this topic in the future....

I bought a 997.1 GT3 and quite happily filled it when it was empty with 55 to 60 litres
Then i took it to an OPC to have cruise control retro fitted
After it was fitted I noticed that I no longer had the option to display sat-nav instructions in the centre display dial in the dash and the fuel gauge would read incorrectly - when it was on red, I could only fill it with a maximum of 33 litres.

Took the car back to the OPC yesterday and they installed the CORRECT software. Now the dial displays the sat nav and the fuel gauge when empty IS empty and it takes 55 to 60 litres to fill it.

Anyone reading this thread in the future, hope this helps.

[vallance5]

V8KSN said:

Sorry to bring up an old thread but for anyone searching this topic in the future....

I bought a 997.1 GT3 and quite happily filled it when it was empty with 55 to 60 litres
Then i took it to an OPC to have cruise control retro fitted
After it was fitted I noticed that I no longer had the option to display sat-nav instructions in the centre display dial in the dash and the fuel gauge would read incorrectly - when it was on red, I could only fill it with a maximum of 33 litres.

Took the car back to the OPC yesterday and they installed the CORRECT software. Now the dial displays the sat nav and the fuel gauge when empty IS empty and it takes 55 to 60 litres to fill it.

Anyone reading this thread in the future, hope this helps.

Nice one , this sounds like what was causing it then as I had cruise control retro fitted a few days after I picked up my car. The satnav arrow didnt disappear but the fuel guage was a problem.

My OPC fitted a whole new tank and sensors and recalibrated the system. Thankfully it was all carried out under warranty, but makes you question what else they may get completely wrong and over charge a paying customer for.

[V8KSN]

vallance5 said:

My OPC fitted a whole new tank and sensors and recalibrated the system. Thankfully it was all carried out under warranty, but makes you question what else they may get completely wrong and over charge a paying customer for.

Is it sorted now ?