Accuracy of the Fuel Guage

Hi all, Any idea how accurate the fuel guage is - both the range left on the computer and the analogue guage? Many thanks

I haven't pushed the range calculation yet, but one time I did calculate my mileage and it was pretty close to the indicated average MPG (within 1 mpg). The range indicator works off of this and mileage, so it should be pretty accurate.

Mine also is pretty accurate, less than 1 mpg.

What I always wonder is: if you are down to Empty, or 0 miles remaining, does that mean you still have the 2 gal. reserve, or does it mean really Empty?

According to the 2007 manual. "Warning light “A” When the engine is running, the warning light of the level gauge lights up if less than approx. 2.6 U.S.gallons (10 liters) of fuel remains in the tank or the range on remaining fuel falls below approx. 30 miles (50 km). Additionally, a warning is displayed in the on-board computer and the central warning light lights up." Might be a good test to see how much mileage your computer says you have left when the warning light comes on, then you can calculate it out yourself.

Both my analog gauge and the digital readouts seem to be in synch with how much gas is actually in the tank.

It means really empty. When the light comes on and you get the message on your dashboard ("consider remaining range" I think it says), you're into the "reserve" such as it is. I've run mine on a long trip down to 2 miles left as indicated on the computer. It was a close as i wanted to get... I put in 16.5 gals... 16.9 is the capacity - so I'd say that's pretty accurate. brad

Thanks for the info - IIRC, the last time I saw the warning light come on, there was still 40 miles or so left on the Info Center, but the gauge needle was still not all the way to Empty. So I guess that "0" miles left, or Empty means you are really empty.

My Cayman 's (analog) fuel gauge is the most linear and accurate that I've seen.

The politeness of the first warning message cracks me up "Consider Remaining Range"

i have run mine until the readout says "-- miles left" and went about 4-5 miles after that because i could not find a gas station . so i would say that they built a small reserve cushion into the readout / gauge .

Thanks chaps - nice to know it is in line with the rest of the car, ie: excellent

Some One Needs to Test This to the Point of Dry Interesting and I hope someone will get back with us if they experience a real strand--dry and not going any further. While I am not sure it'll be either AOK for the drive train or convenient, it would be a significant contribution to understanding the cars and to the CC.

My previous car (a 2002 Jag) had a trip computer also. Was dropping my wife off at the Orlando airport then got on Rt 528 eastbound, only to notice my "estimated range" click down to zero miles. 400 yards later I coasted to a stop......... Don't push your luck with a trip computer unless you are prepared to do some walking..........

I parked mine at 10 and when I started it again, it read --.

I keep my tank above 1/2 generally. I try to keep it full, as condensation builds up and most vaporizes into the exhaust , though some gets to the oil. And a 1% water content in the oil isn't a good thing. Long term, I suspect that it is much worse for the engine than running out of gas. Having said that, the lowest I have run on a trip was down to 32 miles remaining. The old 356 was nice, you just drove until sputtering occurred and then reached down and turned the valve to reserve, assuming you turned it back to main after the last fuel stop

OK, with this thread fresh in my mind, I got to wondering. Two days ago my gas light came on, which seems to happen at a calculated 50 miles remaining. I was out and about at the time and didn't have time to fill up. I continued driving until I had 28 miles remaining. My car has been averaging around 19 mpg, so I should have had about 1.5 gallons left. When I filled up, I took on 14.807 gallons. The car has a 16.9 gallon tank, so 16.9 - 14.8 = 2.1 gallons still in the tank. The computer was off by 0.6 gallons, in my favor (meaning the indicator would have hit 0 and I would have still had about a 1/2 a gallon). Is that accurate? Yeah, I think so. Especially if you consider how the remaining mileage is determined. The computer does the math. Remaining Fuel x Average MPG = Remaining Distance. The fact that it can accurately measure remaining fuel is amazing. But the real fudge factor comes from the varying Average MPG. If you have been going real easy on it and it tells you 50 miles remaining, then you start really working the loud pedal, don't be surprised if you go only 20 miles and are empty.

GB - this very much depends on how you're driving - the computer is constantly re-calculating the mileage remaining depending on how you're driving at the moment - for instance, when I run an autocross or DE event, when I leave, the mileage remaining actually begins to go higher because I was getting 9 mpg on the track, but driving home, the car is now getting 25 mpg... Also, with your fill-up, are you sure you got all the gas into it the 2nd time that you had in the previous tank? brad

I agree that it does depend on how you are driving. I'm sure part of the equation is based on what you are driving right now. I'm sure a higher weighted portion is based on what you have done historically but I'm not sure if that's some different running average in the computer or the average mpg on the readout that you haven't reset for the last 12 months. I was wondering about this before because the miles-to-empty-tank never seemed useful to me - it is obviously conservative in my experience. Consistently, when the low fuel warning is on, I will get in the car and note the change in miles to go and it wont change for miles at a time. Sometimes the mileage even goes up. Then the next time I start the car, the miles to go is even lower but wont change again for another couple of miles of driving. I normally drive pretty conservatively with short random bursts of lets-see-how-fast-we-can-accelerate periods. I think you always have more miles to go then indicated; however, if you only have 10 miles to go (and I have never done that) there is no more room to be conservative and you run out of gas as indicated.

Not sure I know what you mean, or why that would matter. Can you ellaborate? Thanks,

I thought it was bad to not burn up most of your gas? I've heard both ways but I remember once hearing that if you never "empty" your tank, all the **** from the gas tends to accumulate at the bottom of your tank??

Also, this is not as much of a problem as in the past because the tanks themselves are made from plastic, not metal anymore... so there's no rust problems inside them like there used to be. brad

I pumped my car to full today. But when I get in, the analog gauge was full but the digital only show 168. Is something wrong here? I have tried switching the engine off and on again. Usually it would be 280+-.

I have noticed that when my last few minutes of driving were "around town, stop and go" driving. I figured that the low mileage reading was the computer's last reference and the range was being calculated accordingly. When I got into a higher mileage situation - out on the highway - the indicated range was recalculated and a higher mileage to empty was shown.

But I have been to the highway and my gas had went down by 1 bar. However, the digital gauge shown 150. Is 1 bar equate to only 18 miles? Can i reset the computer or something?

Interestingly - or rather, nerve wrackingly! - I had a track day yesterday and had the fuel guage down to the bottom of the red light bit. It was a nervy trip after to the nearest gas station and I got 58litres in. Apparently it has a 64litre tank so still had 6 litres left. I'm not going to test it out though!

I ran mine out of gas tonight because i forgot to go to the station on the way home. Is there anything you guys would recommend to put in to help it clean out etc or just fill up as normal and carry on? its a 2010 pdk S?

Just now nearing the end of a road trip, freeway driving (24-25mpg), 09 987 6m std. Fuel display said I was gonna be short a few miles so I slowed down from 80 to 72, on cruise. After 10 minutes it looked like I wasn't gaining enough, needed 50, display said 45, so I stopped and splashed in a gallon. Fired it up and instead of the range jumping to 70 or so it dropped to 40! Got on freeway anyway thinking it just didn't notice but it never did. I let actual gauge get to the point of just touching the 0 hashmark (btw the display hit 10 and then went right to ---). Stopped for another 1.4 after 44 miles. Display --- and gauge had continued to drop to middle of hashmark, bisecting the 0. Filled up 10 miles later with 14.8 gallons, display & gauge at full. So, things get weird best empty, best to stay away!

It's not so much cleaning out stuff - as it is the fuel pump not being happy because of the lack of fuel. The fuel cools the fuel pump - and running it dry unfortunately sometimes leads to it failing some time later. I realize it is way too easy to ignore the warning message that comes on.. last time mine came on I was right close to a station, so I filled it up immediately. Took 12.8 gallons. I believe the tank capacity is 16.9 gallons - so I still had about 4 gallons left - or about 80 miles to empty. The miles remaining on the display are usually 70 when the warning turns on. The most I've ever put in mine is around 14.8 gallons, and I believe it was telling me I had about 20 miles left.