# Thread: How can I measure the amount of fuel i use?

1. ## How can I measure the amount of fuel i use?

Does anyone know what the device that new cars use to measure how much fuel is used at a given moment?

I want to measure the efiiciency in an older engine that I'm using for an experiment on fuel efficiency. What i need is a way to measure how much fuel passes through the fuel line - like a counter of some sort. Any ideas?

2. You can purchase an aftermarket digital fuel economy meter, or if you are working with an older engine, you can use a manifold vacuum gauge.

Some information at this site to get you started.

You can purchase an aftermarket digital fuel economy meter, or if you are working with an older engine, you can use a manifold vacuum gauge.

Some information at this site to get you started.

I don't think that gadget reports fuel displacement - it just calculates the mileage. I'm looking for the displacement data.

Doesn't manifold vacuum refer to the air? I'm hoping to measure only the actual fuel used. Measuring the air would be a interesting bit of data to though so I'll probably use it! Thanks!

4. Originally Posted by kingcarrot
I don't think that gadget reports fuel displacement - it just calculates the mileage. I'm looking for the displacement data.

Doesn't manifold vacuum refer to the air? I'm hoping to measure only the actual fuel used. Measuring the air would be a interesting bit of data to though so I'll probably use it! Thanks!
Does your cars speedo have a Tachometer? One of the resettable ones to measure trip distances?

5. Originally Posted by Trippy
Does your cars speedo have a Tachometer? One of the resettable ones to measure trip distances?
I think your rerin to a tripometer, which counts distance in kms (or miles). I'm not concerned with distance.

I am trying to measure the actual fuel consumed in my experimental motor. Thanks though!

6. Originally Posted by kingcarrot
I think your rerin to a tripometer, which counts distance in kms (or miles). I'm not concerned with distance.

I am trying to measure the actual fuel consumed in my experimental motor. Thanks though!
So...

Here's what you do.

Do a bunch of driving.

You can read the number of km's you've travelled between topups straight from your tripometer.

And here's the trick - the amount of gas you top your car up with the second time represents the total amount of gas used in your driving.

You can then use this to calculate your fuel consumption - the number of miles you travel between topups divided by the amount of gas you put in your car the second time.

So if you do 100 miles worth of driving between topups, and put 10 gallons in it the second time, then you're getting 10mpg.

Admittedly, this is a time averaged value, rather than an instaneous value, but anything else is going to require specialist equipment to read the output from the tank sensor (it uses a variable resistor, a lever, and a float), the amount of power consumed by the fuel pump, or some other equipment that you will have to purchase and seems likely to cost around 200 USD.

7. They are common on boats.

I've got two fuel flow meters on my Cruiser.

But they would work on any car as well.

http://www.boatersland.com/fuelflow.html

8. kingcarrot

If you are doing bench testing you can use graduated cylinders, a timer and spreadsheet. Low tech and fiddely, but accurate. I helped a guy who was doing octane experiments and that's how we did it. My job was to keep time and make gas remaining entries in the spread sheet. Or you could buy a flow meter, they're relatively inexpensive in some cases and you may be able to get a used one off a car in a junk yard. Simply putting in a known quantity of fuel and timing how long the engine runs is a cheap and simple solution.

Grumpy

9. Didn't you just come off of a ban for multiple posts? Why would you do it again? This is the same post as the one in Arcitecture and Engineering.

You can purchase an aftermarket digital fuel economy meter, or if you are working with an older engine, you can use a manifold vacuum gauge.

Some information at this site to get you started.

I hope this doesn't sound too sexist....but that TOTALLY sounds hawt coming from the lips of woman.

11. I understand you have to calibrate those carefully to measure fuel. I don't think they are tapping in to any kind of volumetric flow information from the engine's computer, but I might be wrong.

12. Originally Posted by spidergoat
I understand you have to calibrate those carefully to measure fuel. I don't think they are tapping in to any kind of volumetric flow information from the engine's computer, but I might be wrong.
There are some that do. I even came across one that taps the the tank reader directly - it's generally for pre-1996 cars, or cars that don't have an ECU. That one though has to be calibrated so that it can learn about the shape of the tank, it plugs into the line that drives your analog fuel gauge.

Basically, you empty out your tank - any fuel left in it will be counted as reserves, fill your tank, stopping up to 16 times to tell the unit how much gas you've put in, and it does the rest automatically.

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