JohnMetro

Does anybody know if the fuel gauge is linear? ie. is the amount of fuel used in the first quarter (from full to 3/4) the same amount as the next quarter tank (from 3/4 to half full)???

I ask because it seems my 964 uses the first 1/4 extremely quickly, but takes longer as the needle goes down. I have only had the car less than 4 weeks, so have only filled it 3 times.

I assume the fuel tank is an odd shape, so the rate of consuption (as read by the dial) will vary?

What is normal fuel consumption for a 1990 manual C4. I seem to go through it fairly quickly, but have also been a bit heavy with the right foot most of the time, too much fun, can't seem to wipe the grin off my face Just got back from dinner with the in-laws, car was nice and warm so I revved through to redline in 2nd for the first time since I bought it... F...uuu.......*#... it nearly scared me!

DaveK

I've never had a car where the guage seemed linear - but they've all been opposite to what you have. They seem to accelerate as the fuel gets lower.

No idea what my consumption is - but I get about 220 miles from a tank if I do short journeys (e.g. 5 miles each way) and about 350-400 miles on motorways.

Geoffrey

The fuel level gauge for the most part is linear although 0 gallons and 1 gallons are the same reading. I had to manually calibrate the fuel level sending unit for my MoTeC dash in the race car and here is the calibration. I have a fuel cell which is the same basic shape and size as a factory plastic tank, so I think the calibrations are similar.

Heirsh

I agree with Dave, altho my 964 has been the best as far as linear readings. Its not perfect and tends to accelerate on me as it gets closer to empty.

My brand new GTi will go so slow down to 3/8 a tank or so then just drop. The computer knows how much is left with reasonable accuracy, but the needle is crazy.

I've never understood why this is such a problem. (or maybe I just bad cars?!?!)

Indycam

I read a story about the way factories set up fuel gauges to read this way and that way . The gauge was made to read out to make the customer happy , not to read right . Some how they mess about with the sender and gauge so that it reads right at full and empty but inbetween they play with it to some how be
"better" than linear .

Dave R.

Early 964 fuel gauge senders were recalled and apparently replaced with senders that read more conservatively toward empty, supposedly due to consumer complaints. PO of my car (1990 C2) grumbled that the original sender was just fine and more accurate at lower levels than the replacement.

seaeagle

I get about 350-400 km in the city and 500km on the freeway which is about the same.

Out of interest is it better to drive around the city at 3,000-4,000 rpm with the odd spurt up to 5500 etc (ie more use of 2nd and 3rd gear in the city- which i presently do and is far more enjoyable) or pot around at 2,000-2500 in 4th/5th gear. Not for fuel economy but for the engine itself.I've heard these motors prefer a bit of work (without always redlining of course!), Just curious.

Bob Krantz

My gauge drops slowly at first (actually stays above full for at least the first 30-40 miles) and then speeds up. It will read about half after 200 miles, but then drop to under a quarter in another 50 miles. I actually plan refills more on the trip odometer than the fuel gauge. My mileage ranges from 20 to 28 miles per US gallon, with 21-22 mpg typical for mixed driving.
Bob K
1989 C4

Busta Rib

I've got a fuel gauge question: when I fill up my tank, the needle only goes up to 3/4 full and never any higher. Is there anything I can do to fix this? I just hate it when things don't work properly on my car. TIA

Indycam

"Is there anything I can do to fix this?"
The system works on variable resistance .
The sender is a variable resistor , a VR .
The read out on the dash "sees" the resistance .

The VR in the tank can be off or broken , the gauge on the dash can be off or broken , the wires in between could be less than ideal .

A classic test is to take the wire off of the sender and then look at the gauge , then ground the wire and look at the gauge , you should see full needle movement , peg to peg . If not then maybe the gauge has a problem .
To test the sender , when you go to the gas station , put a dvm on the sender and watch the resistance while the tank is being filled . The resistance should run smoothly from empty to full without hiccups or stoppages in between .

Of course you are going to be messing around with gasoline and electricity , so be very extra careful not to blow up yourself or your car .

When the tank is good and drained , how much gas can you put in ?
How big is the tank ?
Do they match up ?
If not , the tank fill vent might be not working so good ?

Busta Rib

Excellent reply. I'll give it a go. I'm getting about 17-18 gals if I get somewhere near empty, so I don't think it is a vent issue but I'll check that as well. I understand the tank capacity is 20 gals. Thank you very much for the help.

newsboy

I get approximately 20 m.p.G. with 93 octane in mixed highway and back roads driving. A little more if just on the highway. Of course this will vary, depending on how you drive.

ScottR

+1 on the fuel gauge reading.

I average around 350 miles and fill up.

I've been tracking my fuel consumption for the last 6 months and I average 24.5 miles to the UK gallon, which I think is about 20.5 US gallons?

That's probably about 75% motorway, 25% up and down gears. Same journey to work and back, on regular unleaded - 95 RON from shell in the UK I think?

Scott
1990 C4