Yes I fixed that mistake but did not make it in my previous post where I stated Delta X/ Total gallons nor did I make that mistake in my post above stating a clarification of my argument. Thank you for point my errors out, I want to be clear about what I am stating cause this is an educational experience( at least from my perspective).

Im only commenting on what I understand of the problem. I asked others how they calculate their mpg by hand without getting an error. It seem that people believe doing it by hand is the best or more accurate way. This can be possible, so I asked how others are doing it. some people replied back with a condescending or snarky manner (you being one of them) and I am simply explain how their simple method is ignoring and effecting the total number of gallons actually burned. Which is impossible to get an accurate reading from the gauge cluster
I am a engineer student. I dont claim nor do I think I know more than others on this forum board. Since I am an engineer student, We do try to find how to eliminate errors in a process and what usually causes errors. I simply noticed an error and questioned it. when I notice something that does not sound right, I will stand up and say something about it. Its simple as that, nothing more noting less. It seems that you don't like to be challenged or be wrong.

Here I took the liberty to simply look up how EPA determines MPG and even they state the same thing I been saying this whole time.





https://www.fueleconomy.gov/feg/how_tested.shtml

 

Not using my instrument cluster/marks. Read the methodology I wrote or look at the link in my post. It is really easy to do. It is very accurate. It has been used for years/even my mother in law knows how to do this.

 

I had a 350Z with a messed up gauge, it would short me sometimes on my fuel in the tank. I Disagree strongly with taking the cluster being correct 100% of the time. I agree the method works but it is not the best.

Yes, I made one small reciprocal error in one post but at least I dont go around spelling c450 like C fo fiddy on all most post. To note, I am only an "a$$hole" to those who are a$$es. I dare you to prove my statement wrong . I haven't said anything out the way to anyone on this forum board. just search my 88 posts. I Also challenge you to visit https://www.fueleconomy.gov/feg/how_tested.shtml and read up on how the EPA determines MPG and come back to me and make a substantive rebuttal to my argument in stead of simple formula errors.

 

None of us have the equipment that the EPA has. I have been using the method I mentioned for years. My Dad may he Rest In Peace did the same thing. With your Mercedes the computer will give you a decent estimate of MPG. How accurate depends on how well the car is calibrated. All of these methods are great if you trying to get better mileage or your mileage goes to the dogs and you are trying to find out why. If you can afford a Benz. You can afford the ⛽ï¸�

 

You might need to take a break and post tomorrow or something when you can think clearly. For the 50th time, WE ARE NOT USING THE FUEL PART OF THE CLUSTER, it is simple math, doesn't involve price, Just the actual fuel pump and the odometer.

Many of us are well aware of the EPA tests, but that has not much to do with what the car actually gets in real life, and nothing to do with what the car gets in any individual tank of gas, which is what the thread is all about and comparing actual MPG with what the car itself calculates. Stop posting about the gas gauge and the EPA and you can join us in the discussion.

 

+1

 

my hypothesis on this whole getting a +/- 2 or 1 MPG difference is due to when they're doing it by hand they are inadvertently introduction round off errors.

There is even one guy in here who claims doing it by hand is 100% accurate.
I feel that both methods ( by hand & MPG shown in cluster) are flawed methods but are good estimations and one is better than the other. I'm not 100% sure, but I bet the cluster MPG is more accurate than the by hand method cause I feel the car can better determine the miles and total fuel consumed from the tank. Now your right about calibration, but im only assuming it is in compliance 99.99% of the time .

 

Haha I what "on all most post"? Yes, I did a play on words there, I'm just glad you put it together. It's about time something in this thread doesn't go over your head.

See, I know you, you're "serious all the time guy," right? Yeah, I know that guy. No one likes that guy...

Furthermore, prove you wrong? The burden of proof is not on me. The burden of proof is on the person challenging the status quo (you). And you have proven post after post that you can not do this. As well as everyone here has defended their position time and time again but it is like talking to a brick wall.

If I were you, I'd sleep this off as z28lt1 suggested. Maybe you can come back with a rational head and realize how big of a stick in the mud you are being.

 

I am at work and multi tasking (mostly messing with yall, since this is more entertaining) so maybe I'm not reading your post correctly or at least understanding y'all process of determine MPG fully. lets start from ground zero.

Your using the fuel pump and odometer. So your taking the fuel pump gallon amount dispensed and your using the miles consumed with the new gas added. you then consume all the new gas dispensed. Next your taking your total miles (finish- start or just reset the trip) over your total gallons dispensed. am I right so far?

So my question is that no one can answer is how do you know the car consumed (used) 20 gallons of gas?

 

We have answered that. Many times in fact. Keep reading, I have 50% faith in you that you'll figure it out.

BTW, it's "you're".

 

exactly, you cant prove me wrong. You can only joke around cause you dont know what to say to defend your 100% accurate method. I'm still waiting to hear how you determine your car consumed the inputted gallons. Please explain that to me Oh one with the c fo fiddy.

all jokes a side, you have kept me entertain at work, and I thank you sean with the fo-fiddy

 

http://m.wikihow.com/Calculate-Your-...fficiency-(MPG)

 

Big Thumps

According to the site
Step 1: Go to the gas station and fill up the fuel tank. This may sting a little, but it is key to getting an accurate reading.

Step 2: Record the mileage. Before even pulling away from the pump, write down your current mileage. We will call this Mileage A.

Step 3:Drive normally. To get as accurate a reading as possible, drive until the tank is less than half full. The longer you can go before getting gas, the better. ( This step involves using the Gas hand AKA the cluster AKA the Gauge AKA what ever synonym we used)

Step 4:
Fill up the tank again. Try to use the same station using the same pump as the first fill up, as pumps may be calibrated differently. This time, pay attention to how many gallons it takes to fill up the tank. This is usually shown at the pump. We will call this Gallons. ( Yes its clear how many Gallons were dispensed, but it is not clear how many gallons were burned)

Step 5:
Record the mileage again. This number we will call Mileage B.

Step 6:
Do the math. The formula for determining your MPG is this:

• MPG = (Mileage B - Mileage A)÷Gallons.
• Subtract Mileage A from Mileage B. This will give you the number of miles you drove since your last fill-up.
• Divide your answer by the number of gallons (Gallons B) it took to fill up your tank. This will give you your car's MPG.

If this is what everyone is trying to explain, then it still does not prove that you consumed all of what you inputted and the # your calculating into the formula. You still refer to the gauge as a reference point to how many gallons were used. This method causes the round off error, as I pointed out and can cause a understandable variance in MPG value you see in your trip. So doing it by hand is not 100% accurate and gives you a estimation value. Just because you know you inputted 10 gallons does not mean you consumed 10 gallons. So in reality, you could have only drove 9.59 gallons (input) out your car since your gas hand does not display gas in digital numerical units of gallons. You also have to assume that your fuel gauge sender is calibration is dead on at both reference observation points.

 

I give up!!!!!

 

I will never cede

Update:
No to be honest I'M done. I was mostly just joking, I really did understand what yall were saying. At the start of it, I thought yall were using the gauge but Your only using the displacement from the empty space to figure out burned gas amount. I mostly only kept the act up cause no one could prove me wrong. They could only say your wrong. But I dont want to mislead anyone who is not speaking up or the hundreds of non- account owners who are reading this thread.

But I was not playing when I was stating about the method provides only an estimation. Gas has different density which can cause it to burn slow or faster Weather and vapors also play apart which effects MPG. I also dont know of a gas station that have 100% gas where I live, our gas is more ethanol-gasoline ( 10% ethanol) blends so that effects the amount of energy produced from a gallon of gas. You can get real technical (which I was doing) with determining MPG so its better to just to say why does it even matter and pick a method that you think is best and assume its true like a politician's promise.

 

I give up too. It's like reasoning with a brick wall.

It makes sense that your work is the type that requires such little mental/physical effort on your part that you can post B.S. all day long. I imagine you as something similar to this:

 

I know you are trying to sound smart, and don't want to admit you are wrong, and probably googled a bunch of crap to see what sticks, but you should really give up. I gave up last night, but since it is a new day for me: you are not being "real technical". You are being "theoretical", which once again, is not the discussion we are having in this thread. We are not trying to determine a theoretical MPG, a calculated standardized MPG, a possible best case MPG, or any of the such. We are determining the ACTUAL MPG. In this case while weather, fuel blend, and a whole mess of others things does impact the MPG (keep googling, you'll find more) it doesn't impact the calculation of the mpg.

Since you would like to to be so "technical" there are a handful of areas that could impact this method that is used over and over by millions of people for decades.

1. Accuracy of the pump - most states test this every 2 years or so, and most are very accurate. But if one has an issue, of course, the calculation will be off.

2. Determining the fullness of the tank. Generally, people use the point when the pump's auto shut-off stops the flow of fuel to the car. However, this is a mechanical operation built into the pump, and will vary some from pump to pump, so unless you use the same exact pump, there is probably a slight variation. The actual percentage that the variation introduces, depends upon the difference, and more importantly, the amount of fuel burned between fill-ups If the variation of the pumps is say, 1/10th of a gallon, if you re-fill after 5 gallons, you have introduced and error of 2 percent. However, if you re-fill after 20 gallons, you have introduced a variation of only .5 percent. You can get around this, by overfilling the tank until it spills out, and then you know you have the same amount each time. However, this is a waste of money, not environmentally friendly, and according to many, can cause damage by allowing fuel to enter the charcoal canister (which is a system I have almost no knowledge of, so you can google that as well as i can).

3. Temperature. As you properly noted (and then improperly described the impact of for this thread's purpose) fuel expands with temperature. Filling up with fuel that it at a temperature of 90 degrees, will result in less fuel than fuel that was filled that was 30 degrees. Again, in theory, this could cause a noticeable error. However, at almost every public fuel station, the fuel is stored in underground tanks, that are fairly temperature stable, particularly over a short time-frame such as a week or two that one ordinarily might have between fill-ups. It isn't the outside temperature that matter, but rather the temperature of the fuel itself, more stable stored comfortably underground. By the way, in Canada, many fuel pumps compensate for temperature, so this issue goes away there and any other places that already compensate for temperature.

4. Automobile's odometer. As that is the part of the calculation, any error in the odometer would result in an error in the calculation. Since you seem to dislike any possible errors, you can have your vehicle's odometer calibrated fairly cheaply, and then correct for the error. You should probably do that every few thousand miles or so, since tire wear will vary the error rate some.

So yes, this calculation isn't perfect, but none of the issues you continue to bring up (price, gas gauge, ethanol content, vapors) impact the calculation.

Also, since you like to talk about EPA and things that impact MPG, Motor Trend does a "Real Fuel" test, where they, in controlled conditions, with real measuring devices, test the MPG of vehicles. This is a great way to compare vehicles between each other, and get a more "real world" MPG than EPA or other tests. However, it does absolutely nothing to help us determine our individual MPG in our environment, for any particular distance.
http://www.motortrend.com/real-mpg/

Can't believe I just spent 15 minutes responding to this. I must be going crazy myself.

 

Nice reply!!! Thanks for doing it.